Chondrichthyes

Text © Prof. Angelo Messina

 

English translation by Mario Beltramini

 

Commonly known as Cartilaginous fishes, the Chondrichthyes are a class, after some a superclass of Gnathostomata infraphylum of Vertebrates equipped with articulated jaws and with paired olfactory organs  whose components distinguish themselves at first glance from the Bony fishes (Osteichthyes)  as having the mouth located in a more ventral position and the caudal fin that usually is asymmetrical.

Typically the body of the Chondrichthyes is covered by small placoid scales and the branchial openings are usually in the number of 5 pairs, more rarely 6-7 pairs, with the first opening forming a spiracle.

Other peculiarities of these fishes are the presence of a spiral valve in the intestine and the absence of the operculum and of the swim bladder.

Structurally, the cartilaginous fishes mainly characterize as having an endoskeleton made up of cartilages always devoid of any trace of bony components, hence the name.

This characteristic has remained unchanged for the last 150 million years, and allows these fishes to be lighter and favours their buoyancy.

The evolutionary history of the Chondrichthyes is difficult to reconstruct due to the lack of fossil remains caused by the rapid dissolution of their cartilaginous skeleton. The only fossil remains that have been found date back to 150 million years ago, to the Devonian (Paleozoic era). The reproduction of these animals is sexual with internal fecundation and usually the males have the pelvic fins transformed into copulatory organs (missipterygius or pterygopodia).

The sexual dimorphism is variously accentuated and usually the males are smaller than the females; in some the difference between the two sexes is very marked like in the Chimaeras (Holocephali) where the males have on the head a toothed appendage with which they cling to the female during the mating.

The cartilaginous fishes include oviparous, ovoviviparous and also viviparous species.

Due to the fact that the cartilaginous fishes usually deliver a modest number of newborns and in conjunction with the fishing activity and with the loss of habitat, the majority of species is considered as being at high risk of extinction.

The Chondrichthyes  comprise over a thousand different species, commonly indicated with the names of Sharks, Rays and Chimaeras distributed into the subclasses of the Elasmobranchia and of the Holocephali.

Subclass  ELASMOBRANCHIA

So called as having flattened gills, and also called with the names of Chondropterygia, they form a subclass of cartilaginous fishes.

To the Elasmobranchia are attributed species where typically the head extends forward in a rostrum and with the mouth, armed with teeth arranged in more series, opening in ventral position.

Other characteristics of the group are the body covered with small placoid scales, the presence of 5-7 pairs of gill openings that communicate with the outside individually and the caudal fin that is rigid.

Like all cartilaginous fishes, the Elasmobranchia do not have the swim bladder and can maintain their buoyancy  by means of the big livers they have that contain remarkable quantities of oil. As a matter of fact, by controlling, through the production and the reabsorption the contents of oil and the dimensions of their liver, the Elasmobranchia are able to compensate for the buoyancy force as well as their energy reserve in case of lack of food.

Of very ancient origin, fossil finds would testify their presence already in the Paleozoic more than 450 million years ago, the Elasmobranchia  present some characteristics that have reached evolutionary levels surpassed only by few other present vertebrates. In the meantime, their basic anatomy still maintains several primitive elements.

Even on a molecular level, in these animals do coexist several ancestral peculiarities together with advanced systems, like that of the immune system  that, albeit different, can be compared to that of the mammals.

Endowed with a particularly acute sense of smell and of an eyesight that has developed mechanisms of considerable efficacy for the vision in low light intensities, to which for the man it would be impossible to see, the Elasmobranchia comprise particularly aggressive species that represent a real danger to humans.

Mostly marine animals, the Elasmobranchia  are widespread everywhere, mostly in the warm seas but also in the temperate ones like the Mediterranean Sea in whose waters about seventy species have been reported.

About the systematics of the present Elasmobranchia among the specialists there is no identity of views, also because of the lack of data, especially fossils.

However, several scholars on the base of a careful comparative examination of the structure of the skull, distribute the about 700 species nowadays known in the superorders of Selachimorpha, Galeomorpha, Batoidea,

Squatinomorpha about which here we shall limit ourselves to providing synthetically the main representative elements.

Superorder  SELACHIMORPHA

Commonly known with the names of Dogfishes or Sharks, the Selachimorpha are cartilaginous fishes (Chondrichthyes) that include species with a typically tapered body, pointed head and the mouth provided with jaws strong and equipped with a large opening in relation to their predatory habits.

Usually the eyes have a nictitating membrane, excepting the members of the orders Hexanchiformes and Lamniformes who do not have them.

The majority of the Sharks is equipped with 5 gill openings placed on the sides of the head, but some have 6 and even 7 of them like the Hexanchiformes.

These fishes have a couple of well developed pectoral fins, one pair of pelvic fins, two dorsal ones of which the first is typically triangular and sharp, one anal fin and one caudal with the upper lobe more developed than the lower one (heterocercal tail). In the males, the apical portions of the pelvic fin are modified in copulatory organs shaped like cigars  (hemipenis), with which, while mating, through the cloaca, the sperm is introduced inside the female genital ways thus realizing the internal  insemination.

The size of these fishes stands between those of the Spined pygmy shark (Squaliolus laticaudus Smith  and Radcliffe, 1912), that does not exceed 22 cm, and those of the Whale shark (Rhincodon typus Smith, 1828), that, with a maximum length of 18-20 m and a weight of more than 30 tons, stands among the biggest extant fishes.

The present Selachimorpha  include about 500 known species that are distributed in different orders of which we give here below information of general character.

Order Hexanchiformes

Apart from numerous extinct species, presently this order, probably the oldest of the Selachimorpha is represented only by about ten species that characterize for having the eyes devoid of the nictitating membrane, 6-7 gill openings, hence in a bigger number compared to that of the other orders, and only one dorsal fin having no rays. Commonly known as Capochiatti and Eel sharks, these fishes have dimensions that vary greatly from species to species.

With only 1 m of length, the smallest is the one from the Southern African frilled shark.

(Chlamydoselachus africana  Ebert and Compagno, 2009), that lives in deep waters off the African coast from southern Angola up to southern Namibia.

The giant of the order, with more than 5 m of the Bluntnose sixgill shark (Hexanchus griseus Bonnaterre, 1788), known also as  Sixgill shark or Cow shark, diffused in tropical and temperate waters.

Another member of the order is the Cow shark or Cinereous knotweed (Heptranchias perlo Bonnaterre, 1788) diffused in the tropical and temperate waters of almost all oceans, including the Mediterranean Sea. This is a species just one metre long that characterizes for the presence of 7 pairs of gill openings.

Order Squaliformes

These are an order to which are ascribed forms  that are characterized at first sight due to the presence of five gill slits and of two dorsal fins, often preceded by a bone, and for the absence of the anal fin. The dimensions are very varied, from just about 20 cm to about 7 m  of length.

Practically widespread in all seas, where usually they prefer the deep waters, the about 130 species included in the order are found in the tropical seas, in the temperate ones up to the cold Arctic and Antarctic seas. In relation to their abysmal habits, several species present adaptations like big eyes and bioluminescence, as is the case of the so-called lantern sharks.

The systematics of the order does not find the specialists in agreement especially for its distribution in families. Presently to the order are ascribed 7 families of which we mention the following:

Family Dalatiidae

Called Kitefin sharks, they form a taxon whose composition is rather controversial especially at the level of subfamilies and genera. Some scholars insert there with the value of subfamily also the Somniosinae  and the Etmopterinae that others consider as other distinct families. Among the species attributed to the Dalaitinae we mention the following:

The Pygmy shark (Euprotomicrus bispinatus Quoy and Gaimard, 1824) is the only species of the genus, with an average length of about 25 cm for the females and of 22 cm for the males, standing among the smallest sharks.

Ovoviviparous animal, delivers 8 pups per litter, has a circumglobal distribution and is found in subtropical to temperate waters.

The  Cigar shark (Isistius brasiliensis Quoy and Gaimard, 1824) known locally as Cookiecutter shark or Cutter shark, is a species of small size, averagely measuring about 50 cm, diffused in all tropical oceanic waters, where it goes deep up to more than 3500 m. In relation to its abysmal habits, it has big eyes and the ventral surface of the body equipped with photophores.

Family Somniosidae

By some considered as a subfamily of the Dalatiidae, they are known with the common name of Sleeper sharks. They include little less than twenty species mostly of dimensions between the 70 and 140 cm, excepting the Greenland shark (Somniosus microcephalus Bloch e Schneider, 1801). Known also with the names of  Arctic shark or Grey shark, is a big fish that may reach 7 m, and is native to the waters facing the north Atlantic coasts of Iceland and of Greenland.

The flesh of this fish is poisonous and if eaten fresh causes in man effects similar to those of a severe intoxication. The sled dogs, if fed with the flesh of this fish, are unable to stand. Nevertheless, in the Nordic countries the flesh of this shark is consumed by the locals after long boiling or dried and left to ferment for some months, obtaining the so-called hákarl.

In Greenland and in Iceland the locals get meat considered a delicacy from fishes buried in boreal lands and left exposed to various cycles of freezing and thawing .

Family Etmopteridae

Considered in some classifications as a subfamily of the Dalatiidae, they are indicated with the name of Lantern sharks due to the characteristic common to all the afferent species of having the body  with numerous photophores forming luminous stripes and dots (bioluminescence),  arranged mainly around the mouth and along the sides, that have the function of attracting small preys in the almost complete darkness.The family includes little more than 40 species among which the Dwarf lanternshark (Etmopterus perryi Springer and Burgess, 1985) perhaps among the smallest members of the order, the male measures little more than 15 cm and the female does not exceed the 20, is a shark living off the coasts of Venezuela and Colombia where it goes swimming in between 250 and  450 m deep waters.

Family Squalidae

Known with the name of Dogfish sharks, Dog sharks and Spiny dogfish, they include species whose dimensions usually reach 100 cm of length in the males, 125 cm in the females. Presently the family is divided in two distinct genera, known with the name Squalus with 34 species and Cirrhigaleus, with only 3 species.

The most known shark in the family is the Spiny dogfish (Squalus acanthias Linnaeus, 1758), fish living on the seabed, usually over 200 m deep, of the coastal zones of the temperate seas all over the world.  The average size of this fish varies between one metre and a maximum of one metre and sixty, with a weight that may reach even 10 kg. The head is relatively flattened with a rather elongated and sharp snout. The eyes are well developed and the mouth is wide and equipped with teeth rather similar to each other.

The common name of the Spiny dogfish is due to the presence of 2 spines located near the dorsal fins, connected with poisonous glands and used for defensive purposes. In man the sting of the Spiny dogfish may cause severe pains and only rarely, in case of allergic reactions, even death.

The colouration is frequently greyish, at times with brownish or greenish hues; on the sides are present white spots usually more evident in the young specimens.

Ovoviviparous animal, after a long gestation that may last even two years, the female delivers already formed and autonomous pups. The Spiny dogfish nourishes of fishes, usually cods and herrings, as well as of invertebrates such as mollusks and krill.

Another member of the family is the Mandarin dogfish (Cirrhigaleus barbifer Tanaka, 1912), species reported for the deep  waters of the tropical and subtropical seas.

Order Pristiophoriformes

Known as Sawsharks, they are considered an order of the Elasmobranchia.

They are small sharks that are characterized for having the head elongated anteriorly in a flat and long rostrum furnished on the lateral margins of sharp protuberances similar to the teeth of a saw and for the absence of anal fin.

The mouth has two long barbels and is equipped with thin teeth of various lengths. The gill openings, in number of 5 or 6, are placed anterior to the pectoral fins.

The Sawsharks resemble morphologically to the Sawfishes included in the order Rhinopristiformes (Batoidea) from whom they differ for various characters, in particular the different position of the gills that in the latter are placed ventrally, the shape of the rostrum and that of the teeth.

Widely distributed in the tropical seas, but mainly in the warmer waters of the Indian and Pacific Oceans, the order nowadays is represented by only 5-6 species ascribed to the only family Pristiophoridae  and distributed in the genera Pristiophorus, with 5 gills, and Piotrema with 6.

Superorder  GALEOMORPHA

They gather sharks commonly known with the name of Dogfishes, which are distinguished because presenting the body usually fusiform with two dorsal fins having no spines and 5 gill openings. With the exception of some species, the spiracles open on the sides of the head.

The Dogfishes have very varied dimensions, from just 1 m of length up to gigantic forms, beyond the 18 m of the Whale shark, that are the biggest among all fishes. The reproduction is ovoviviparous.

Mostly diffused in the tropical seas, whilst some are found in all the seas and few have adapted themselves to the life in freshwater, the Galeomorphi unite more than 300 species, mostly ascribed to the order Carcharhiniformes.

Other orders are Heterodontiformes, Lamniformes  and Orectolobiformes.

Order Carcharhiniformes

They represent the group with the biggest number of species, just under 300, that characterize for the presence of the nictitating membrane on each eye, for the position of the pectoral fins decidedly after the five gill openings.

Furthermore, they have two dorsal fins and one anal.

These Dogfishes have quite different dimensions varying from a length of about seventy centimeters in the sharp Australian shark, to more than 5 m in the Tiger shark.

It must be said immediately that several species are difficult to identify and that recent studies on the DNA have evidenced that some groupings are not monophyletic and that they suggest a revisit of the systematic character of the whole order.

Practically diffused in the marine waters of the whole world, only few species are able to go up the river courses, these sharks include very known species, several of which are indicated as Requiem sharks. This term is of controversial etymology, after some coming from the Latin requiem (peace), conversely, after others, from the French requin (shark), others more, always from French reschignier (“to grimace while baring the teeth”).

Here below we provide some essential information concerning the most known members of the order.

Family Galeocerdonidae

Considered by some scholars a subfamily of the Carcharhinidae, nowadays they are represented uniquely by the Tiger shark Galeocerdo cuvier ( Péron and Lesueur, 1822), known also as Sea tiger for the dark stripes along the body that resemble a tiger’s pattern. The stripes fade greatly with age. Of very large size, it may measure more than 5 m and weigh about one ton, the Tiger shark is found in tropical and temperate waters, more frequently in the central zone of the Pacific Ocean.

Of preferably night habits, this shark is a solitary hunter of a huge variety of animals and is so voracious to even swallow inedible objects of anthropic origin, deserving the nickname of garbage can of the sea. Even if it happens very rarely, the Tiger shark is believed to be second only to the Great white shark in the deadly attacks to man.

Family Carcharhinidae

Known also as grey sharks or grey reef sharks they form a family that after some scholars gathers 12 genera to whom are ascribed good part of the species of the order, some of them aggressive to man.

The genus richest in species is Carcharhinus  of which we mention the following.

The Bull shark (Carcharhinus leucas Müller and Henle, 1839), also called Zambezi shark or Bull shark referring to its squat shape with the short and flattened snout and to its erratic and aggressive behaviour, is a species loving the warm and little deep waters of the coastal zones of all the world; unlike most of the other sharks is able to go upstream in the water courses. It is considered as standing among the most dangerous sharks for man.

The Oceanic whitetip shark (Carcharhinus longimanus Poey, 1861)  is an about 4 m long fish that distinguishes due to the long and rounded fins with white tip, hence its name of Oceanic whitetip shark; because of this characteristic it is often mistaken with the Whitetip reef shark (Triaenodon obesus).

Widespread in the warm tropical and temperate seas, it is an aggressive shark that is one of the greatest dangers for the survivors of air or sea accidents.

Presently the number of Oceanic whitetip sharks has significantly decreased due to an increase of the fishing activity against it as its fins are highly sought after as main ingredient in the famous shark fin soup.

The Grey reef shark (Carcharhinus amblyrhynchos Bleeker, 1856) is the member of the order among the most common. in the Indo-Pacific waters, from the Red Sea to South Africa, where it loves to live in the waters close to islands and coral reefs.

Small animal, usually does not reach the length of 2 m, with broad and rounded snout and big eyes, this shark characterizes for presenting the first dorsal fin of a uniform colour or with a whitish dot on the tip, unlike the other fins that have the tip black.

It is rather similar to the look of the congeneric Blacktip reef shark from which differs for the dot on the dorsal fin.

Despite the modest dimensions, the species is responsible for several attacks on humans.

Object of intense fishing, these sharks are considered endangered for their low rate of reproduction as well as for the reduction of their habitat.

The Blacktip reef shark (Carcharhinus melanopterus Quoy and Gaimard, 1824) is one of the species of Carcharhiniformes more diffused in the coral reefs of the tropical waters of the Indian and Pacific Oceans, where it loves the shallow coastal waters, with sandy bottoms or coral platforms.

Animal of medium length, usually about one metre and a half, is often mistaken with the congeneric species Blacktip shark (C. limbatus Müller and Henle, 1839) and Grey reef shark (C. amblyrhynchos Bleeker, 1856), from whom differs for the presence of showy black spots at the expremity of the fins, in particular of the first dorsal and the caudal one.

Rarely dangerous for man, the Reef blacktip shark is not considered important on the commercial point of view even if its flesh is utilized together with the fins and the liver oil.

The species is considered as endangered due to the excessive fishing, its low reproductive rate and its habitat degradation.

The Caribbean reef shark (Carcharhinus perezi Poey,1876),  diffused in the tropical waters of the western Atlantic is quite common in the Caribbean Sea waters. Averagely three metres long, it is more frequent in the coral reef where it represents one of the biggest predators of fishes and of cephalopods.

The Spinner shark (Carcharhinus brevipinna Müller e Henle, 1839) is a dogfish that on average reaches lengths of about 3 m. It has a slender body with elongated snout and presents the characteristic of having the fins adorned by black dots on the tips. Usually a gregarious animal, it is found in coastal waters and open seas, with preference on shallow bottoms.

Skilled predator, it eats a variety of cephalopod mollusks and of bony fishes. Its habit of hunting passing rapidly through the schools of fishes rotating around its own axis and partially moving out of water has made it deserve the English name of “spinner shark”.

The Spinner shark is reported practically in the waters of all the oceans and it seems that specimens coming from the Indian Ocean have also reached the Mediterranean through the Suez Canal.

Nevertheless, presently the actual range of this species cannot be defined with certainty considering that, also due to the uncertainty of the diagnostic character, is often mistaken with other species and in particular with the Edged shark or Lesser blacktip shark (Carcharhinus limbatus Müller and Henle, 1839). Object of fishing due to the remarkable importance on the commercial point of view, for the flesh, for the liver oil and the skin, the Spinner shark is also a coveted prey for the sport fishermen.

The Blacknose shark (Carcharhinus acronotus Poey, 1860), also called Carcarino, is a small shark that usually measures more than one metre of length. Its body is slender with an elongated and rounded muzzle presenting one typical black dot on the tip, and only one small dorsal fin. The Carcarino lives usually in the tropical and subtropical waters of the Atlantic Ocean, in environments generally characterized by sandy, stony or covered by weeds, bottoms. Little aggressive animal to humans, it is considered endangered because of the excess of fishing it undergoes.

And more, among the most known members of the family is not to be forgotten the Blue shark or Verdesca (Prionace glauca Linnaeus, 1758), so called due to the dark blue colouration on the back, whilst on the sides and ventrally is whitish. Known also under the name of Verdesca, this shark has a pointed head with an ample mouth and armed with sharp and triangular teeth. The body is tapered and in the males may reach almost the length of 3 m, whilst in the females can reach 3,5 m and even overcome them. Typically, the caudal fin presents the upper lobe remarkably more developed than the inferior one, about 4 times.

Lives preferably in deep waters, tropical and temperate, all over the world where it can do long migrations.

The Lemon shark (Negaprion brevirostris Poey, 1868) is a fish that is just under three metres in size who owes its name with which it’s commonly indicated to the brown-yellowish, like the zest of a lemon, colouration of the back; the belly is whitish. It is diffused in the open and brackish waters of western and eastern Atlantic and in those of eastern Pacific.

The Whitetip reef shark (Triaenodon obesus Rüppel, 1837), only membre of the genus, is a small shark, usually it measures about 150 cm in length, and is reported in the waters of the Indian and Pacific oceans as one of the most common species of the coral reefs.

The species is characterized for its slender body, with short but broad head, equipped with two typical tubular dermal appendices placed close to the nostrils. The dorsal and caudal fins have white margins.

Of nocturnal habits, this dogfish nourishes predating mainly mollusks, crustaceans and fishes; only rarely it gets aggressive towards man. Like many other species of the order, the populations of the Whitetip reef shark have progressively become poorer in terms of number of specimens especially due to the increase of the fishing activities whereby the species is presently considered as vulnerable.

Family Leptochariidae

They are represented by only one genus with the only species commonly indicated with the name of Barbeled houndshark (Leptocharias smithii Müller and Henle, 1839), This fish is known also with other names, such as Atlantic dogfish, Bearded dogfish or Carcarino.

It is a small fish, approximately 80 cm in length, that is recognized due to the presence of dermal appendages departing from the nostrils, hence one of the names with which it is usually called. The males of this species distinguish at first sight from the females as presenting the teeth that develop in a very enlarged fore tusk.

It is reported for the waters of the eastern Atlantic Ocean, from Mauritania up to Namibia, where it frequents the muddy bottoms and the mouths of the rivers.

Family Scyliorhinidae

The Catsharks and the Small-spotted catshark are the names under which are commonly called the numerous species, more than 150, included in the family Scyliorhinidae. The common name of these fishes is due to the elongated shape of the eyes remembering those of a cat.

The body of these small sharks is decorated with stripes or simple spots and presents two small dorsal fins placed far back on the body.

Most species are minute in size, usually not longer than 80 cm and only exceptionally exceed 150 cm. Amongst the many species attributed to the family, practically diffused in all tropical and temperate seas, are to be mentioned following species.

The Nursehound or Greater spotted dogfish (Scyliorhinus stellaris  (Linnaeus 1758), stands within the species of the bigger-sized family measuring even 1,7 m of length. The body of this shark is pale brown with brown and yellowish punctiform specks. It lives in the Mediterranean waters and in those of the eastern Atlantic Ocean, from Guinea up to the North Sea, where it is found on the rocky bottoms, seaweed expanses and coral zones in low and medium depth.

The Small-spotted catshark (Scyliorhinus canicula Linnaeus, 1758) is the shark most diffused in the Mediterranean Sea and is found also along the eastern coasts of the Atlantic Ocean, from Guinea up to the North Sea and the Baltic Sea and also in the Black Sea. Its livery is similar to that of the Greater spotted dogfish with beige background colour speckled brown and yellowish, but displays thicker and minute spots. The two species are widely fished and commercialized all over Europe.

Family Sphyrnidae

They comprise a group of species commonly known as Hammerhead sharks that owe their name for the structure of the head that presents unusually flattened and laterally spread assuming a typical hammer shape or cephalofoil.

Of variable size from just under 2 m up to 4 m, the Hammerhead sharks have the eyes located at the two lateral extremities of the extension of the head that allow an excellent 360 degree stereoscopic vision.

It is speculated that the unusual configuration of the head, with the fact that it increases considerably its surface and its particular richness of Lorenzini ampullae is to be related with the remarkable capabilities these animals have of orienting themselves by means of the earth’s magnetic field and to perceive the even weak electric fields produced by other living organisms. The remarkable development of the sense of smell contributes in rendering these sharks fearsome predators.

Of predominantly nocturnal habits, the Hammerhead sharks are diffused in all seas of the world where they keep mainly in the warm coastal waters and on the continental shelves.

Currently the family includes about ten Hammerhead sharks that, making exception of the Winghead shark that is the only member of the genus Eusphyra, are all ascribed to the genus Sphyrna. Within the species of the family are to be remembered the following.

The Scalloped hammerhead (Sphyrna lewini Griffith & Smith, 1834) is a big animal (more than 4 m long per a weight that may reach 300 kg), that populates the tropical and subtropical coastal waters of all oceans, including the Mediterranean Sea, where it loves the bays and the estuaries.

The Great hammerhead (Sphyrna mokarran Rüppel, 1837)  is a big shark, it may reach even 6 m of length, that characterizes the ample cephalofoil, with almost straight fore profile but a short central indentation. The body has a grey-brown colouration on the dorsal parts, pale on the ventral ones.

The first dorsal fin is rather high and sharp, with an arcuate rear margin. It is found in almost all warm temperate and tropical seas more frequently in the coastal zones. As the summer season approaches, this shark usually undertakes long migrations towards cooler waters. Due to its imposing mass and its aggressiveness, it is probably the most dangerous hammerhead shark.

The Bonnethead (Sphyrna tiburo Linnaeus, 1758 ), is the smallest member of the genus being, averagely, about 90 cm long, and only exceptionally may reach 150 cm. Characterized by the hammer that is smaller than that of the other congeneric species, it is also known with the name of shovelhead due to the head rightly shaped like a shovel. Among other things, this species, unlike the other sharks, distinguishes for an evident sexual dimorphism concerning the morphology of the head.

As a matter of fact, when adult, the females have the head smooth and amply rounded, whilst the males, due to the elongation of the rostrum cartilages, present an evident swelling of the anterior margin of the hammer. It is a species diffused in the coastal waters of both sides of the American continent where it also frequents estuaries and bays with muddy and sandy seabeds. In the northern Atlantic is found up to the Gulf of Mexico and Brazil. In the Pacific waters the species is common from southern California up to north Peru.

This uncommon shark characterizes also for being the only known species of the order having omnivorous eating habits.

The Winghead shark (Eusphyra blochii Cuvier,1816),  usually less than two metres long and with the first dorsal fin high and falciform, owes the common name to its “hammer (cephalofoil)” remarkably developed laterally, that can reach half the total length of the shark.

The nostrils are quite ample and open on the fore margin of the cephalofoil and probably contribute to a better detection and perception of the traces of smell in the water. The distribution range of this fish includes the tropical waters of the Indian and Pacific oceans, from the Persian Gulf up to Taiwan where it usually frequents the coastal zones, estuaries and bays. This species, harmless for man, is abundantly fished for the fleshes, of reasonable commercial value, in order to get from them liver oil of high nutritional value and fishmeal.

Family Triakidae

Other members of the order Carcharhiniformes are included in this family that gathers species with oval eyes and equipped with a nictitating membrane, with the two dorsal fins spineless and presenting the anal fin.

Among the about 40 species attributed to the Triakids, the most well-known ones are two sharks whose dimensions are around two metres in length.

The Common dogfish (Mustelus mustelus Linnaeus, 1758) or Smooth dogfish, is a species that is found on the continental shelf of the eastern Atlantic and in the Mediterranean Sea.

The Starry dogfish (Mustelus asterias Cloquet, 1821)  is a medium-sized shark, usually about 100 cm long with the back of brownish grey colour dotted with white, hence the common name. It lives in the eastern Atlantic waters and in the Mediterranean ones.

To the family is ascribed also the Leopard shark (Triakis semifasciata Girard, 1855), so called due to its characteristic livery that on the ventral parts is white whilst the remainder of the body is of grey colour variously shaded. The dorsal parts are adorned with a series of wide ovoid brown dark-edged spots that alternate with small roundish spots of the same colour, whilst the sides are marked by a horizontal line of big brown spots.

The Leopard shark is diffused in the temperate and cold waters of the north-western Pacific Ocean, where it is preferably found in coastal waters of estuaries and bays with sandy and muddy bottoms.

Order Heterodontiformes

They are considered an order, after some scholars, conversely, a suborder, of sharks that maintain characteristics of primitiveness, such as the presence of a strong spine preceding each one of the two dorsal fins and the oviparity.

Commonly, they are called Bullhead sharks because of the massive structure of the body, with the stocky head having a rounded snout, whose size usually does not exceed the 150 cm. The abdominal region is considerably flattened.

The mouth, located at the extremity of the snout and located anterior to the eyes, has the upper lip adorned with

cutaneous lobes. The teeth, arranged in successive rows, are numerous and of various shape, hence the name of

Heterodontiformes. 

The central teeth are small and sharp, whilst the lateral ones are big and flat, molariform, good for grinding the mollusk shells and the shells of the carapaces, animals on which these sharks mainly nourish of. The Bullhead sharks are represented by about ten species, all ascribed to the only genus Heterodontus, diffused on the bottoms of tropical and subtropical waters of the Pacific and Indian oceans.

Among the most known species stand the Port Jackson shark (Heterodontus portusjacksoni Meyer, 1793) reported for the coastal regions of southern Australia, the Japanese bullhead shark

(Heterodontus japonicus Miklouho-Maclay and MacLeay, 1884) typical to the coastal waters of Japan, the Horn shark (Heterodontus francisci Girard, 1855)  and the Crested bullhead shark  (Heterodontus galeatus. Günther 1870), diffused in the waters of eastern Australia.

Order Lamniformes

They represent an order that gathers species of sharks with a fusiform body and characterized by morphological and behavioural particularities very different from each other. They do not have the nictitating membrane and have a huge mouth extending even behind the eyes. All components of the order have five pairs of gill openings, two dorsal fins and one anal fin.

They are medium to large sized sharks whose length varies from about 3 m to 10 m and even more of the Basking shark. Prominent components of the oceanic ecosystems during the Cretaceous, period in which they reached their maximum diversity, the Lamniformes  subsequently suffered a sharp reduction during the mass extinction of the Cretaceous-Paleocene (about 66 million years ago) that caused the disappearance of many species of vegetables and animals, among which the dinosaurs.

Nowadays, of the hundreds of species with which in that period the ancestors of the present Lamniformes did populate all the seas, remain just about twenty species of which we give the essential distinctive elements. In addition to the group of species known with the name of Mackerel sharks, are also to be mentioned the Bullhead sharks, the Goblin shark, the Megamouth shark and the White shark. Some species are dangerous for man.

Family Odontaspididae

They form a family of sharks Lamniformes whose species are characterized for the ample shape of their teeth, hence the scientific name. Commonly known with the names of Sand tiger sharks (Carcharias) and Sand tigers (Odontaspis), they are big fishes, more than 3 m long, and are found in the coastal tropical and temperate waters of all seas, Mediterranean included.

The Sand tiger shark Carcharias taurus Rafinesque, 1810), diffused in the coastal waters of the whole world, and the Indian  sand tiger shark (C. tricuspidatus Day, 1878). found mainly in the Indian Ocean. In both cases they are two big predators whose dimensions may exceed the length of 3,5 m.

Family Mitsukurinidae

They form a family tho which is ascribed only one extant genus with the only species, the Goblin shark (Mitsukurina owstoni Jordan, 1898), Known also as Elfin shark, this fish mainly distinguishes due to the snout elongated into a long rostrum that resembles a beak, with long and protrusible jaws. The body is almost uniformly pink coloured.

The Goblin shark lives in the oceanic abysses of all the seas of the world, in particular of Japan.

Family Pseudocarchariidae

They include deep sea fishes, of which is only known the Crocodile shark (Pseudocarcharias kamoharai Matsubara, 1936)  It is a species of which poor information is available on its morphological characteristics as well as on its actual distribution. It is reported mainly for the Pacific Ocean, but also for the north-western Indian Ocean and for the eastern Atlantic.

Family Megachasmidae

Represented only by the Megamouth shark or Megamouth (Megachasma pelagios Taylor, Compagno and Struhsaker, 1983), they are considered as a family of Lamniformes This species owes its name to the ample mouth that may exceed even the metre of width. The teeth are small and arranged in series, up to 50 series in the upper jaw and up to 75 in the lower one.

The body is robust, averagely about 4 m long in the males and 5 m in the females, with bulbous, long and broad heads. The tail is asymmetrical with a long upper lobe that recalls that of the Atlantic thresher. In relation to its planktivorous food habits, this shark has the inside of its gill slits covered by gill rakers.

The species has been found in the temperate and tropical waters of the oceans with greater frequency in those of the western Pacific in depths between 5 and 1.500 m.

Family Alopiidae

They are a family of sharks Lamniformes to which is attributed only the genus Alopias. It is a genus divided into 3 species commonly known with the name of Thresher shark due to the characteristic caudal heterocercal fin with the  upper lobe significantly stretched recalling the tail of a fox.

These are sharks whose dimensions vary from the 3 to six m of length, with fusiform body or brown-bluish colour on the dorsal parts and paler in the ventral ones; the two dorsal fins are small and the pectoral ones are falciform.

Like the dolphins, the Thresher sharks are able to leap above the surface of the water.

Of solitary habits, they are diffused in the tropical and temperate seas where they prefer the open coastal waters.

Utilizing the characteristic tail also to stun and overwhelm the preys, the Thresher sharks feed on animals living in schools, frequently squids and mackerels.

Among the species attributed to the genus the following are to be mentioned.

The Common thresher or Atlantic thresher (Alopias vulpinus Bonnaterre, 1788), very diffused in the tropical seas and that with about 6 m of length is the biggest in the genus.

The Pelagic thresher (Alopias vulpinus Nakamura, 1935), reported as common in the Indian and Pacific oceans and that with about 3,5 m of length is the smallest member of the genus.

The Bigeye thresher (Alopias superciliosus Lowe, 1841), called also Big-eye shark is a fish just under 5 m long, per a weight of 364 kg presenting a circumtropical distribution and has been sighted in the Mediterranean Sea from Gibraltar Strait up to the Strait of Sicily.

Family Cetorhinidae

Also this family of Lamniform sharks is represented by only one genus to whom is ascribed the Elephant shark or Cetorino (Cetorhinus maximus Gunnerus, 1765),  only extant species. Called also Basking shark this shark owes the common name of elephant, besides its huge size, 10 m and even more, to the fact of possessing, during the first years of life, a particularly elongated and prominent snout that recalls a proboscis.

It is considered the second biggest fish presently living on Earth  after the Whale shark (Rhincodon typus Smith, 1828)  of the order Orectolobiformes.

Easy to recognize due to the huge mouth that when eating is wide open and to the considerably developed dorsal fin, the Elephant shark is found in the oceans and in the temperate seas. Slow and absolutely harmless to humans, this giant of the seas feeds mainly on plankton,  weeds or microscopic animals it swallows through its big mouth.

Family Lamnidae

They are considered one family of the order Lamniformes that presently is divided in 3 genera that group just 5 species of which we mention the following. The great White shark or Carcharodon (Carcharodon carcharias Linnaeus, 1758) is the only member presently extant of the genus.

It is a big fish, averagely about 4 m in the males and 5 m and even more in the females, with conical snout, dark and round eyes.

The mouth is armed with several rows of teeth particularly long and pointed as evoked in the scientific name.

Besides being sharp, the teeth are also of various shapes, sharp on the lower arch to bite and hold the prey, triangular and serrated on the upper one for tearing it apart.

Typically, the first dorsal fin of the White shark is big and falciform and is implanted at the level of the rear end of the pectoral ones, they too, sickle-shaped. The second dorsal fin and the anal are small.

The tail displays the peduncle with an ample keel on each side and the caudal fin is big and half moon shaped, with the upper lobe slightly more developed than the lower one.

The colour of the body gets usually hues variable from grey to blue on the dorsal parts, white in the ventral.

Of pelagic habits, the White shark is more frequent in waters particularly rich in possible prey, such as colonies of seals, sea lions and penguins.

With a practically cosmopolitan diffusion, this shark is found in the coastal superficial waters of all main oceans, especially in the cold or temperate ones, excepting the Baltic Sea and the North Sea. The White shark is reported also in the Mediterranean Sea where it has a reproduction zone in the Strait of Sicily. This species has not been reported in the Arctic and Antarctic seas.

In this respect is to be told that studies on the genetic patrimony of the White shark have evidenced the striking similarity between the Mediterranean populations and the Australian ones, instead with the Atlantic ones as might be expected. These studies support the hypothesis that the White sharks of the Mediterranean are the descendants of specimens that arrived from Australia more than 400.000 years ago through the Gibraltar Strait and that were no longer able to get out from the same.

The Mako shark (Isurus oxyrinchus Rafinesque, 1810),  commonly known as Shortfin mako shark or Oxyrin, is a species widely diffused in all tropical and subtropical waters and is present also in the Mediterranean though quite rare.

Of medium to large size, usually measures about 2,5 m but may reach even a length of 4 m per a total weight of more than 500 kg, this shark has fusiform body marked by longitudinal grooves, with small pectoral fins and the caudal fin presenting the two lobes having the same development. Particularly agile and unpredictable in the attacks, it is a smart predator usually of blue fish and also of tunas and is considered as standing along the most dangerous sharks for man.

Like few other sharks, in particular the Blacktip reef shark and the White shark, Mako shark is able to jump out from the water (breaching), even up to 7 m high from the surface. The Porbeagle shark or Sea calf (Lamna nasus Bonnaterre, 1788) is a shark whose dimensions are around 3,5 m. It lives in the Atlantic, Indian and Pacific oceans and is present also in the Mediterranean where it reaches a depth of 400 m.

Typically, the Sea calf has a secondary keel at the base of the tail. The body has a colouration varying from grey-blue to brown with white spots.

The Pacific porbeagle (Lamna ditropis Hubbs and Follett, 1947), more known as Salmon shark, is a fish whose dimensions can reach the length of 3 m and the weight of 250 k. Usually, females are bigger than the males. The colouration of the body is uniform and varies from black to grey-bluish on the dorsal parts, whilst on the ventral ones is white. Active, fast and aggressive, the Salmon shark is a terrible predator living in the cold northern waters of the Pacific Ocean from Alaska to the Bering Sea up to Japan, where it mainly preys on fish, like herrings, tunas and salmon, hence the common name of Salmon shark.

Order Orectolobiformes

Considered by some scholars an order and after others a suborder, they group sharks that are characterized by the elongated body, hence the name. The mouth, small and located anterior to the eyes, is provided with a barbel. The gill slits are small and are five, the fifth of which partially overlaps the fourth. The two dorsal fins are spineless.

They are known also with the name of Carpet sharks as most of them have the body adorned by drawings that evoke the patterns of the carpets. They include about 40 species of which the most known are the so-called Blind sharks, the Nurse sharks and the Whale sharks.

Family Brachaeluridae

So called for the characteristic of having two dorsal fins close together and without spines, and the caudal fin little developed, they are a family of sharks Orectolobiformes.

There are 2 attributed species, both endemic to the coastal and shallow waters of south-western Australia, commonly known with the name of Blind sharks. However, despite the common name, these sharks are not blind being provided with eyes.  They are sharks of small dimensions, usually little more than 50 cm and little more than 1 metre long, with two barbels, grooves around the nostrils and big blow holes.

The Blind shark (Brachaelurus waddi Bloch and Schneider, 1801) distinguishes especially for the bigger size from the Bluegrey carpetshark or Colcloughs shark (Brachaelurus colcloughi Ogilby, 1908) that usually measures averagely 50 cm in the males and 65 cm in the females.

Family Ginglymostomatidae

They form a family to which are ascribed species known as Nurse sharks due to the mouth shaped like a hinge that is utilized like a bellows for sucking up the prey they feed on, such as crustaceans, mollusks, fishes.

They are sharks with flattened bodies, whose dimensions usually vary from 75 cm to more than 4 metres of length, with short and broad snout, barbels of various length, large nasal grooves and small spiracles behind the eyes that are oval. They have two spineless dorsal fins and one anal fin; the tail is very short and strongly asymmetric.

Animals of usually nocturnal habits, if disturbed these sharks may be dangerous for man.

The family is diffused in the tropical and subtropical coastal waters of all oceans, more frequently on the coral reefs close to the shore. To the group are ascribed few species of which the most known are the following.

The Nurse or Nurse shark (Ginglymostoma cirratum Bonnaterre, 1788) is a shark also just over 4 m long. It is found usually in the western waters of the Atlantic Ocean and is reported also for the Mediterranean.

The Pacific nurse shark (Ginglymostoma unami Del Moral-Flores, Ramírez-Antonio, Angulo and Pérez-Ponce de León, 2015) is typical of the tropical waters in the eastern Pacific.

The Tawny nurse shark (Nebrius ferrugineus Lesson, 1831) has a more slender body and is usually 3 m long. It is met in the tropical coastal waters of the Indian and Pacific oceans.

Finally, the Short-tail nurse shark (Pseudoginglymostoma brevicaudatum Günther, 1867),  long less than 1 m is reported for the western tropical waters of the western Indian Ocean.

Family Hemiscylliidae

Called Bamboo sharks, they represent a family of Orectolobiformes whose components are characterized for having the more or less shortened muzzle with the nostrils located at the apex of the snout itself or close to it. They have short barbels and a big blowhole.

The Bamboo sharks have the body slim and tapered, usually less than 120 cm long, with the tail usually longer than the rest of the body.

Just under twenty species are known, grouped in 2 genera of which we mention the following:

The Brownbanded bamboo shark (Chiloscyllium punctatum Müller and Henle, 1838), also called Brown spotted catshark due to the presence of barbels looking like a mustache, distinguishes for the rear dorsal fin that is concave.

This fish is found in the waters of the western Pacific Ocean where it loves the coral reef. It is considered at risk of extinction, due to the fishing activity and the pollution of its habitat.

Another bamboo shark is the Hemiscyllium galei Allen and Erdmann (2008),  small fish of usually about 60 cm, known for the curious peculiarity of walking on the bottom using the fins.

It lives in the coral reef of the bay of Cenderawasih on the northern Indonesian coast.

The Indonesian carpetshark (Hemiscyllium freycineti Quoy & Gaimard, 1824) is known in the western coastal waters of New Guinea.

The Speckled carpetshark (Hemiscyllium trispeculare Richardson, 1843) lives mainly in the western Pacific waters.

Family Orectolobidae

Carpet sharks is the name with which are often commonly indicated species attributed to various families of the order Orectolobiformes.

They are sharks that differ for the presence of outgrowths similar to small plants around the mouth and in particular of dark mimetic drawings arranged symmetrically on the back that recall the decorations of the carpets.

The Carpet sharks are found in the temperate and tropical shallow waters of the western Pacific and eastern Indian oceans.

Of the eleven species ascribed to the family Orectolobidae, are to mentioned the most known ones:

The Spotted wobbegong (Orectolobus maculatus Bonnaterre, 1788), three metres long on average, lives along the coasts of Japan, southern China and those of Australia.

The Tasselled wobbegong (Eucrossorhinus dasypogon  Bleeker, 1867) is one metre long or little more that is found in the western waters of the Pacific Ocean.

Family Parascyllidae

Conversely, with the name of Collared carpet sharks are named the species united in the family Parascyllidae.

They are sharks with long and tapered bodies that usually do not  reach the metre of length. Equipped with barbels under the mouth, these fishes have the eyes that recall those of a cat, provided with a nictitating membrane.

Presently 8 species of Collared carpet sharks are known, among them Parascyllium ferrugineum (McCulloch 1911),  endemic to southern Australia and Parascyllium variolatum (Duméri 1853), also coming from the south of the Australian continent.

Family Rhincodontidae

Also included among the carpet sharks is the Whale shark (Rhincodon typus Smith, 1828). The only species of the family Rhincodontidae, with the 18,8 metres of length registered until now, the Whale shark represents the biggest fish currently extant and the biggest among the living non-mammalian vertebrates.

The common name, besides the remarkable size, refers also to its filtering food habits that do not differ from those of the whales. As a matter of fact, the Whale shark presents a very big mouth that unlike many other sharks opens in the fore part of the head and is equipped with a filtering apparatus.

This is formed by several rows, even more than 300, of tiny teeth and 20 plugs that allow the animal to nourish almost exclusively of plankton and of small fishes.

In the sharks, such modality of feeding is found only in other two species, the Elephant shark and the Megamouth shark, both attributed to the Lamniformes. The pectoral fins of the Whale shark are very ample and are located under the last two gill slits, whilst the two dorsal fins and the pelvic ones are of modest development.

The caudal fin has the two lobes similar with the upper slightly longer.

Another characteristic of the Whale shark is the presence on the body of small protuberances arranged in  checkerboard that stand out on the white dotted livery on blue-greenish background; the ventral parts are whitish.

Despite the appearance that surely arouses fear, this gigantic shark does not pose a threat for man, who can safely approach it though paying attention not to be inadvertently bumped by its enormous size.

Mainly pelagic fish, it lives in all tropical and temperate seas with temperature of the water usually exceeding 21 °C.

It frequents coastal and open seas environments, usually at medium depths but that, exceptionally, may reach even 2000 m.

Animal of migratory habits, it periodically originates aggregations of seasonal feeding in several coastal sites of which the most frequented are the Persian Gulf and the Gulf of Oman, the coastal waters of the Seychelles, of India, Taiwan, southern China and also the coastal waters of Darwin Island in the Galápagos, those of the eastern coast of the Peninsula of Yucàtan in Mexico and Ningaloo in western Australia.

Right in the coastal waters of the Yucatán the Whale shark annually forms seasonal aggregations in the period between May and September including a huge number of specimens, at times up to 400 and even more. The phenomenon has caused the rapid growth of ecotourism flows that have already reached unsustainable levels.

Family Stegostomatidae

The Zebra shark (Stegostoma fasciatum) Hermann, 1783,  probable synonym of  Stegostoma tigrinum Forster, 1781) is considered the only extant member of the family Stegostomatidae  and owes  the common name to the fact that the young individuals have the dark coloured body marked by characteristic yellowish stripes similar to those of a zebra. With maturity the livery changes and the adults display a reddish body tipped with black.

Of medium size, it usually measures about 2,5 m of length and only rarely may reach the 3,5 m. The Zebra shark has a very slender body and is equipped with particular crests, with rounded snout and provided with barbels. Typically, the caudal fin is very developed, about as long as the rest of the body. It is a fairly diffused shark in the coastal waters of the Indian and Pacific oceans.

Superorder  SQUATINOMORPHA

They form a particularly interesting group that form species whose morphology is wholly peculiar assuming morphological and structural characteristics of the sharks Orectolobiformeses,  such as body fusiform in its rear part, as well as of the rays Batoidea, like the big development of the pectorals that unite to the head forming the typical disc.

However it is to be kept in mind that the resemblance of the species of this superorder with the Batoidea  is to be attributed by the scholars exclusively as an evolutionary parallelism. They include one only order, Squatinoformes, with the only genus Squatina.

Order Squatinoformes

They form an order where are comprised species with the body, stocky and broad in front, tapered and squaliform in the rear. These fishes are characterized by bug pectoral fins, hence the name of Angelsharks with which they are commonly called. In most species the dimensions do not exceed the metre and a half of length and only in some instances they can reach the 2,50 m.

The Angelsharks, also called Squadrons, have big mouths armed by long and sharp teeth and with extendable jaws, in relation to their predatory habits. The eyes and the spiracles are located over the head, whilst the five gill stilts open below in front to the pectoral fins.

Besides the pectoral fins, also the ventral (pelvic) ones are quite broad. There are two dorsal fins whilst the anal fin is missing. Typically, the caudal fin has the lower lobe more developed than the upper one.

The Angelsharks have the habit of staying on the bottoms and covering of sand while waiting for prey, represented by crustaceans, mollusks and other fishes; in these situations the water reaches the gills through the spiracles.

Usually not aggressive, the Angelsharks are viviparous animals and usually give birth to 7 to 13 pups at a time.

Family Squatinidae

With only one family and one only genus (Squatina), to whom are ascribed a little less than twenty species, the Angelsharks are amply diffused in the tropical and temperate seas where, with few exceptions, they prefer the shallow waters with sandy bottoms. Following species are reported in the Mediterranean waters:

The Monkfish (Squatina squatina Linnaeus, 1758) is the most known species of the family and differs from the other congeneric for the knurling that, besides covering the back, extends also on the lateral-ventral parts with smaller and rounded denticles. The head, big and stocky, has the mouth in terminal position with on the sides a flap of skin and 4 barbels. The species is diffused in the eastern Atlantic, from southern Norway to the Canary Islands, and in the Mediterranean.

The Sawback angelshark (Squatina aculeata Dumeril in Cuvier, 1817) is recognizable due to the big head with on the sides a skin fold bearing 2-3 protruding triangular lobes. The back, covered by bony spinulae, is marked longitudinally by 2 grooves delimiting 3 rounded keels.

Behind the head and up to the first dorsal fin is present a median row of spines, larger and having a broad base shaped like a star. The body has on the dorsal parts a colouration more or less grey-brown with marblings and a big white dot at the base of the pectorals. The ventral parts are clear.

It is a species of the eastern Atlantic and of the Mediterranean where it has practically disappeared. In Italy it is mentioned for the Ligurian Sea and for the Tyrrhenian Sea. It is a species considered at extreme risk of extinction.

The Smoothback angelshark (Squatina oculata Bonaparte, 1840) is a shark that is recognized due to its relatively slenderer and thinner body than the other congeneric species and for a skin fold without triangular lobes placed on the sides of the head.

The back, devoid of mediodorsal spines, has some longitudinal grooves that delimit 3 to 7 keels. The body of this species gets on the back a colouration fading from brown-reddish to brown-greyish with darker marblings and small white ocellar spots regularly arranged, hence the specific name. Each side of the caudal peduncle is adorned by three pairs of great dark ocelli. The Smoothback angelshark lives in the eastern waters of the Atlantic ocean and is found also in the Mediterranean ones. Also this species is considered at risk of extinction.

Superorder  BATOIDEA

Known with the name of Rays, they are considered as a superorder of Cartilaginous fishes (Chondrichthyes).

The Batoidea group forms that distinguish for having a flat body with enlarged pectoral fins and shaped like wings that usually merge with the head forming a typical disc. The anal fin is absent. The eyes and the spiracles are placed over the head. The mouth opens ventrally and is able to stretch considerably the upper jaw for seizing the prey. The most accredited classification of this group, by far the richest in species among the Cartilaginous fishes, more than 600, even if is still to be confirmed on solid phylogenetic basis, identifies its subdivision in the orders of the Rajiformes, Rhinopristiformes, Torpediniformes and Myliobatiformes.

Order Rajiformes

They are considered an order to which are ascribed species, commonly indicated with the name of Rays, that characterize for a huge variety of forms quite often of difficult individuation at specific level.

The dimensions of the Rays stand usually between little about 20 cm to 2,5 m. Usually these fishes have a depressed body that together with the pectoral fins, widened and transformed in “wings” often completely merged to the head and the trunk up to the pelvic fins, forming a singular structure, called disc.

The disc is more developed in length and has various shapes (wedge, triangular, oval or circular). Only in a few species the head is not part of the disc. The rostrum is variously pointed depending on the species.

This particular shape of the body represents a clear adaptation to the bathypelagic life that favours these fishes in moving more freely on the seabeds and in hiding into the sand in case of presence of dangers.

This peculiar conformation of the body allows the Rays to swim more slowly but with a great elegance, characteristic that has attributed these fishes also the name of “angels of the sea”.

Also the mouth of the Rajiformes, placed transversely and provided with small obtuse teeth transformed in masticatory plates, forms a further adaptation allowing the shredding of the preys with hard shell like mollusks and crustaceans living stuck to the marine substrate.

The tail, variably long and equipped dorsally with protective spines, is separated from the disc and has lost its primary propulsive function. The movement of the Rays is totally entrusted to the pectoral fins.

Usually the skin of these fishes is thick, smooth and covered with mucus or provided with spine and bony tubercles that vary from species to species for dimension, shape and arrangement.

The gills, present in a number of 5-7 pairs, have an elongated shape like in the other Elasmobranchia and are arranged ventrally.

In the species living on the seabeds (benthic) usually the eyes and the spiracles are placed on the top of the head.

In the Rays, the sexes are neatly distinct with an evident sexual dimorphism that appears very early already in the embryos, even before the occurrence of the differentiation of the gonads.

Already upon birth, the male pups  are characterized by the presence of two big copulatory organs that originate on the medial margin of the two pelvic fins (missipterygius  or  pterygopodia).

Like in all other cartilaginous Fishes, also in the Rays the reproduction is the sexual one with internal insemination.

While mating, the male holds the female, seizing it with its own teeth. Then, by means of its pterygopodia, introduces the sperms inside the upper genital tract of the partner, before that the nidamental  glands deposit around the egg the protective ovule structures (membrane and horny shells).

In the ovoviviparous Rays the embryo nourishes of secretions produced by the maternal uterus or of other substances and the female delivers already formed pups.

The oviparous Rays, deposit the fecundated eggs rich in vitellium (telolecithal eggs), protected by a strong horny shell of variable shape and provided of long spiralled filaments through which they attach themselves to rocky or coral substrata. After about six months hatch from the eggs the pups who drag like a sort of umbilical cord the residual of the yolk sac.

Well representative of the order is Rhina ancylostoma  (Bloch and Schneider; 1801)  only extant and until now known of the family Rhynidae,  reported in the coastal waters of the Pacific and Indian oceans.

The Rajiformes  are an important element of the marine communities and form a fundamental link in the vital cycle of the oceans.

Social animals, they often gather even in numerous schools that may be formed even by hundreds of individuals. They form a grouping to which affer little less than 300 species who for the most part live in marine waters where they prefer the sandy and muddy bottoms.

Of sedentary habits, the Rays live in surface and shallow waters, albeit rarely they may be met up to 3000 m of depth. Conversely, some species spend a good part of their life in brackish waters of deltas and estuaries, whilst there are few ones who have even colonized the fresh waters of streams located even thousands of kilometres far away from the coasts.

Since the most ancient times these fishes have been fished by humans who, besides the goodness of the flesh sought for due to their delicacy, have also exploited them for different purposes, getting leather from the skin, necklaces and even clubs from the tail, spearheads from the stings. Today as well, the Rays continue in being object of very active fishing all over the world, and are amply utilized in the kitchen as well as in the fashion industry for obtaining luxury items, such as shoes and handbags.

From a systematic point of view, the order of the Rajiformes forms a group very heterogeneous to which is attributed an unspecified number of species, after some specialists little less than 300 species, conversely, after others, a much higher number. This discrepancy is due to the fact that their classification turns out to be quite difficult due to the uncertainty of the diagnostic characters employed, in particular at specific level, as well as for the lack of research made difficult because the fact that of many of these fishes few information are available as they live in the ocean depths.

Family Rajidae

It is no coincidence that in the last two decades have been described more than a seventy species previously not known. Because of such taxonomic uncertainty, in this text we deem right to focus on this family, among the richest of the order and to which affer several species diffused in the waters of the Mediterranean and of the northern Atlantic, Baltic and North Sea included. Among these should be remembered the Thornback ray (Raja clavata Linnaeus, 1758), a very common species at depths varying from 20 to 100 m, as well as in the waters of the Atlantic, from Iceland up to Morocco, also in the Mediterranean and in the Black Sea. About 1m long averagely, the Thornback ray owes its own name to the presence of numerous big stings on the upper part of the body.

Another species of the genus is the Blonde ray or Blonde skate (Raja brachyura Lafont, 1873) of eastern Atlantic where it lives preferably on the sandy or muddy bottoms where it reaches depths of almost 400 m. Just over one meter in length, the adults of this species that owes its name to the shortness of the tail, have the upper part of the body wholly spiny.

With the name of Common skate or Blue skate, Flapper skate or Grey skate is indicated the biggest ray that reaches a length just under 3 m. Described by Linnaeus in 1758 with the specific name of Raja batis, since some time this species has been attributed to the genus Dipturus with the name of Dipturus batis  (Linnaeus, 1758).

Actually, still today the systematic status of this ray is not entirely clear. Some scholars propose to divide the species into two entities, one, northern, larger in size (Dipturus intermedius) and the other, southern, smaller (Dipturus flossada).

Taxonomic considerations aside, the common ray was in the past the most abundant ray in the north-eastern Atlantic and in the Mediterranean. Presently due to the intense fishing activity, the populations of Dipturus batis  have significantly reduced and the species has been inserted in the Red List IUCN among the endangered species.

Finally, fairly rare in western Mediterranean waters is the Undulate ray (Raja undulata ( Lacépède, 1802),  species that, conversely, is amply distributed along the eastern coasts of the Atlantic. About one meter long, this fish has the typical appearance of the family it belongs to, with the snout equipped with a short rostrum and the mouth armed by 40 to 50 rows of teeth on the upper jaw. The very developed pectoral fins, hence the specific name. On the median part are present several spiniform processes that concentrate along the median line and on the tail.

Order Rhinopristiformes

In this order are presently comprised the species commonly indicated with the names of Sawfishes, Guitarfishes and Violinfishes. Actually, whilst there is agreement in attributing the rank of family to the Sawfishes (Pristidae) and the  Guitarfishes together with the Violinfishes (Rhinobatidae), there is rightly no identity of views concerning the systematic position of these two families.

In fact, whilst some scholars insert the two groups within the Rajiformes,  others instead consider that the

Pristidae  are the only extant members of an order by itself, that of the Pristiformes. Others still gather Pristids and Rhinobatids in the Rhinopristiformes,  orde to which some ascribe also other families. Actually, the fact remains that the phylogenetic position of these groups is not yet clearly defined.

Consequently, we deem appropriate here to treat together the two groups, also considering that for some common morphological characteristics, if on one side Pristids and Rhinobastids differ from the Rays (Rajiformes), especially for having a squaliform body, on the other side they rightly differ from the Sharks as presenting pectoral fins enlarged and merged with the head in a disc rightly like in the Rays. Also on the families that are affered to this group, the scholars are not in agreement. In view of this, we will focus here on the Pristidae (Sawfishes) and Rhinobatidae  (Guitarfishes and Violinfishes).

Family Pristidae

This is a family to which are attributed forms, commonly known as Sawfishes, that may reach about 6-9 m of length, two of them pertaining to the rostrum, dimensions standing among the biggest between all  Chondrichthyes. In addition to the squaliform body, the members of this family differ at first sight also for having the skull developed anteriorly in a flattened rostrum, about a quarter of the body long.

On the margins of the rostrum is present a series of little less than 20 to 32 robust dentiform placoid scales arranged in regular intervals and about 5 cm long and similar to teeth, that give it a look of a saw, hence the common name. The eyes are small, placed in front and two ample spiracles. The mouth opens in a ventral position, behind two bilobate nostrils. Moreover, these fishes are provided of two large dorsal fins and of a long heterocercal caudal fin. The Sawfishes do not have anal fins.

Diffused in the tropical and temperate marine waters, where they usually populate the shallow waters, the Sawfishes utilize the rostrum to move the bottom looking for crustaceans, mollusks and also other fishes they eat.

Some species even enter the rivers. To the Pristidae  are ascribed about 8 species, distributed in two genera, of which we give here some essential distinctive elements.

The Smalltooth sawfish (Pristis pectinata Latham, 1794)  is a big animal, even more than 7 m long, per about a weight of 350 kg, is a species typical to the Atlantic tropical and subtropical zones where it loves the shallow waters with sandy or muddy bottoms. Especially when young, this fish frequents the brackish waters of bays and estuaries, at times even going up fresh water streams. It is a species considered at high risk of extinction.

The Dwarf sawfish (Pristis clavata Garman, 1906) lives in the waters of tropical Australia seas and with its average length of about 3 m is the smallest species in the Pristids.

The Common sawfish (Pristis pristis Linnaeus, 1758), by some called also Largetooth sawfish, is often mistaken with other species of the genus also due to the few available data. Also its dimensions are poorly utilizable for its identification being reported as comprised between 2,5 to more than 7 m of length.

Also the colour of the body, rather variable from the ocher grey to brown-reddish on the back and cream white ventrally, cannot represent a good diagnostic character. The rostrum has no more than 20 pairs of teeth.

It is considered species diffused in mainly tropical or subtropical zones where it is reported in coastal waters, in brackish waters of estuaries and lagoons and occasionally also in water streams. Its presence in the Mediterranean waters is to be confirmed.

The Longcomb sawfish (Pristis zijsron Bleeker, 1851) is even more than 7 m long with a rostrum that may exceed 1,5 metres in length. It is found in the range extending from the African eastern coast up to the South-East Asian islands and to the northern Australian waters. Due to the colouration of its back that sometimes gets greenish colours, this fish is also known with the name of Green sawfish. Object of fishing, the Longcomb sawfish is considered at critical risk of extinction.

An ample range is attributed to the Pristis microdon (Latham, 1794), species with an uncertain taxonomy to which are given various synonyms. Commonly known as Largetooth sawfish, the species is reported for the waters of the In dian and Pacific oceans, from eastern Africa to New Guinea, northwards up to the Philippines and Vietnam, and south, up to Australia.

It loves the shallow bottoms, sandy or muddy, of coastal waters and the brackish waters of rivers that it ascends up to freshwater lakes where it seems it reproduces. Huge animal, it may reach even the length of 7 m, has a tapered saw equipped with 22 teeth per side.

The Narrow sawfish (Anoxypristis cuspidata Latham, 1794) is the only species of the genus. It has medium dimensions that are around 4,5 m and characterizes for the rostrum that is equipped with up to 33 pairs of teeth. It frequents the sandy bottoms of marine and brackish waters of the estuaries of the rivers from the Red Sea up to Japan. It is a species deemed in danger due to the fishing activity and the deterioration of its habitat.

Family Rhinobatidae

It is a family whose membres are known as Guitarfishes and Violinfishes due to their resemblance, albeit vague, with those musical instruments. Conversely, the scientific name of the family they belong to (Rhinobatidae), literally, rays-nose, probably refers to the presence of a rostrum on the snout. Also these fishes characterize for having the elongated body, more or less flattened or compressed laterally. But, unlike the Sawfishes, in these fishes the pectoral fins extend also anteriorly to the gill slits, without however reaching the extremity of the snout.

Usually the eyes are placed on the top of the head, allowing a better vision of the surrounding environment. The head of these fishes, broad and depressed, is partially fused with the pectoral fins to form a typical triangular structure that in front extends in a rostrum of various development. The two dorsal fins are more or less equal to each other, the caudal one is well developed.

Animals basically ovoviviparous, oviparous in some instances, are subdivided in an indeterminate number of species, most likely more than 50, distributed in about ten genera, among which Rhinobatos  to whom are ascribed most of the species, Pseudobatos,  Zapteryx, Trygonorrhina and Glaucostegus, to which is ascribed the Giant shovelnose ray (Glaucostegus typus), in the past attributed to the genus Rhinobatos  with the name of Rhinobatos typus. Following are synthetically represented the most known species with the main distinctive elements of the most well-known forms.

The Shovelnose guitarfish (Rhinobatos productus Ayres,1854) is a species that like the others of the genus has a laterally compressed body, squaliform, with the typically flattened horizontally head, ample and triangular, fused with the pectoral fins. The other fins are triangular and the caudal one has only one lobe and is membranous.

The body is brown greenish uniform on the head, back and sides, whilst the ventral parts are almost white. Behind each eye opens a great spiracle provided with 2 folds. The dimensions, different in the two sexes, in the males reach a maximum length of 120 cm, whilst in the females they even reach the 170 cm.

It lives in shallow waters of the American western coast, from the Gulf of California to the Bay of San Francisco.

The Violinfish (Rhinobatos rhinobatos Linnaeus, 1758), called also Common guitarfish, is a species living on the shallow sandy or muddy bottoms of the Mediterranean, especially in its southern waters, and of eastern Atlantic, from the African equatorial coasts up to the Gulf of Biscay, France.

Like the other species of the genus, the Violinfish has a long body with the anterior half depressed, of triangular shape and prolonged ahead in a pointed snout with raised median rostrum.

At the centre of the snout stand two characteristic cartilaginous longitudinal rostral crests slightly converging in the anterior part.

The eyes are small and dorsal and behind each stands a spiracle.

In ventral position open the nostrils that are bilobate and the mouth that is small and provided of flat teeth, suitable for grinding the shells and the crustacean and mollusk shells of which, together with other fishes, they feed.

The pectoral fins are amply developed and adhere to the head forming its rear edges.

Always ventrally appear on each side five gill slits, of small size.

Conversely, the rear part of the body is tapered, more similar to that of the sharks.

The two ventral fins, of practically equal dimensions, are clearly distinct and have a triangular shape.

In both sexes the anal fins are absent and in the males the pelvic ones are modified in two hemipenes. The caudal fin is triangular and does not present distinct lobes.

The colour of the body is grey with brown-yellowish shades on the muzzle, whitish in the ventral parts. Usually the margins of the fins are of light colour or of intense yellow.

The dimensions, different in the two sexes, generally slightly exceed one metre in length in the males, whilst the females may reach the metre and a half and even more.

The Blackchin guitarfish (Rhinobatos cemiculus Geoffroy Saint Hilaire, 1817), is a species native to eastern Atlantic Ocean, from Portugal up to Angola, and of the Mediterranean Sea where it is sympatric with the Violinfish, from which it distinguishes mainly for having smaller eyes and narrower rostral crests more convergent ahead.

Averagely about 180 cm long, the Blackchin guitarfish has the body brown on the dorsal parts and white on the ventral ones. On the snout stands out a characteristic black spot, more evident in the young individuals. Like the other species of the genus, it usually lives on the seabed preying invertebrates, such as crustaceans and mollusks and small fishes. Subject to strong fishing pressure, mainly for its fins, presently this species is considered heavily at risk.

The Atlantic guitarfish (Pseudobatos lentiginosus Garman,1880), by some considered synonymous of Rhinobatos lentiginosus (Garman, 1880), is one of the smallest of the family, reaching an average length of 70 cm and 2,5 kg of weight. Like in the other congeneric species, in this fish the snout extends forward in a rostrum and the pectoral fins are fused with the head to form a triangular disc. The mouth opens ventrally and is equipped with numerous small teeth, about 80 per jaw, suitable for crushing of shells and carapaces of the preys this animal eats. The body has a colouration varying from yellowish to brown and is adorned by small white dots scattered on all the body that recall the lentigos, hence the specific name.

This species lives in the coastal waters of Atlantic up to north of Gulf of Mexico, even going as far as the Caribbean Sea It preferably frequents the sandy and muddy seabeds, where it nourishes of mollusks, crustaceans and at times also of small fishes it immobilizes on the bottom with the help of the rostrum. If threatened, this fish sinks into the sand of the bottom utilizing the rostrum like a shovel.

In the Atlantic waters the Chola guitarfish (Pseudobatos percellens Walbaum, 1792), lives, whilst in the Pacific ones is reported the Banded guitarfish (Zapteryx exasperata DS Giordano & CH Gilbert, 1880) recently attributed to other family (Trygonorrhinidae) on the base of the mitochondrial DNA analysis.

Another species of the family is the Eastern fiddler ray (Trygonorrhina fasciata Castelnau, 1873),  diffused in the coastal waters of eastern Australia. Known with various other names, such as Banjo shark, Fiddler ray, this fish reaches dimensions tha usually are of about 120 cm. It characterizes for the ovaliform disc with rounded snout and the back adorned by wide pale violet bands with dark edges tha include a triangular mark located on the head just behind the eyes. It loves the rocky or sandy seabeds where it hides for catching crustaceans and other invertebrates it eats.

Order Torpediniformes

They are an order of Chondrichthyes  that unites species characterizing for the presence of typical generating organs formed by specialized muscular tissue and located on each side of the head, able to produce discharges that, depending on the species, may vary from 50 to 220 volts. The bioelectric impulses are controlled by the nervous system and after a certain number of discharges, the animal needs a resting period before being able to produce new ones.

Known also with the name of Electric rays, referring to their flattened shape that somewhat recalls the Rays of the order of the Rajiformes, these fishes have the body without scales, with pectoral fins well developed and merged with the head to form a flattened disc. The gill slits are located ventrally.

Predatory animals, they usually are lurking on the sandy and slimy seabeds waiting for possible preys that they stun or kill with their own discharges.

The order, where are ascribed about seventy species, is diffused mainly in the waters of the Atlantic, Pacific and Indian oceans.

In the Mediterranean are reported the Ocellated torpedo or Torpedo (Torpedo torpedo, Linnaeus, 1758) that lives on the sandy and muddy bottoms between 5 and 100 m of depth, the Marbled electric ray (Torpedo  marmorata Risso, 1810), known locally also as Spotted torpedo or as  Numbfish and the Black torpedo (Torpedo nobiliana Bonaparte, 1835) that is the biggest species in the genus and that goes to depths exceeding the 400 m.

In the open waters of the Indian Ocean and of the Red Sea, lives the Panther electric ray (Torpedo panthera Olfers, 1831), fish that averagely measures about 1 m of length. Known also as Leopard torpedo this animal is found in the sandy or muddy shallow waters and also on the coral reefs.

The  Gulf torpedo (Torpedo sinuspersici Olfers, 1831), called also Variable torpedo ray or Marbled electric ray, lives in shallow marine and brackish waters and close to coral reefs of western Indian Ocean, of Persian Gulf and of the Red Sea.

The presence of this species also in the Mediterranean where in the past has been reported is to be confirmed. Frequently, it buries itself in the sandy or muddy bottom.

The Ocellated electric ray (Diplobatis ommata DS Giordano & CH Gilbert, 1890) is so called due to a characteristic drawing on the centre of the disc formed by a roundish black or yellow spot surrounded by concentric rings. Known also with the name of Bullseye electric ray, it is a small, about 25 cm long, fish, native to the coastal waters of central-eastern Pacific.

The Lesser electric ray (Narcine bancroftii E. Griffith & CH Smith, 1834), commonly known with several other names among which Spotted torpedo ray and Brazilian electric ray, usually lives under the sand or the mud of the western shallow coastal waters of the Atlantic Ocean and of the Caribbean Sea. Just under 50 cm long, this fish has a roundish body with short tail, that on the back gets a colouration varying from dark brown to reddish brown. It is equipped with two electric organs that may generate discharges that can reach just under 40 volts.

Order Myliobatiformes

More commonly known as Stingrays, Pelagic stingrays, Rays, some also as Common eagle rays, others as Bull rays, they are considered an order of Cartilaginous fishes  (Chondrichthyes) to which are ascribed forms usually with oval or rhomboid shape, considerably pressed dorsally and with the pectoral fins very developed, shaped like wings, that merge laterally with the head.

The dorsal fin is just sketched out and implants at the root of the tail or is completely missing. The anal fin is absent. The eyes are placed on the back, the mouth opens ventrally and is provided of several small teeth suitable for crushing carapaces and shells of the animals it eats. The gills open on the ventral part of the body.

On the snout are located sensory cells that form the so called Ampullae of Lorenzini, organs that, as already said in the general information of the Cartilaginous fishes, are capable to perceive low frequency vibrations of the water and then of the electrical field.

The tail, of variable length, at times long and thin, similar to a whip, is armed above with a long sting that in the bigger specimens may measure even fourty centimetres of length and presents a typical serrated profile. At the base of the sting are poisonous glands that secrete substances that in the prey produce strong muscular contractions and have a necrotizing effect that destroys the cells, often with a fatal outcome also for man. Some species have several stings.

The dimensions of the body of these fishes are various and in the bigger species they may reach even the length of 4 m.

Benthic animals, they usually live staying on the seabeds covered by sand or by mud. They are mostly found in salt waters but exist also fresh and brackish waters forms. Most of them are ovoviviparous, but some species are oviparous and lay horny-shelled eggs.

Presently at the order are ascribed several forms profoundly different from each other, altogether about 130 species, some of which are found also in the Mediterranean. Previously included in the order of the Rajiformes, nowadays the  Myliobatiformes  are considered a monophyletic group to which is attributed the status of distinct order.

However, among the scholars there is no identity of views about the systematic categories of lower level, in particular families and genera. Considering the disparity of views on the systematics of this group, here we limit ourselves to a brief overview of the most known forms.

The Southern stingray (Dasyatis americana Muller e Henle, 1841), known also as Common stingray, is a fish that can reach even the 2 m of length. It is diffused in the tropical and subtropical waters of the Atlantic Ocean, where it frequents the sandy shallow bottoms and the lagoon waters. Of mainly night habits, it nourishes of benthic animals, such as invertebrates, in particular mollusks and crustaceans and also of small fishes. By some experts, the Southern stingray is considered  as a synonym of the Whip stingray (Hypanus americanus Hildebrand & Schroeder, 1928), also diffused in the tropical and subtropical waters of western Atlantic.

On sandy or muddy seabeds even at depths exceeding the 450 m off the African coasts of the Indian Ocean and in the waters of Australia and New Zealand lives the Short-tail stingray (Dasyatis brevicaudata Hutton, 1875).

It is a species of large dimensions, even more than 4 m long with a weight of more than 350 kg. The body has a colouration that on the dorsal parts varies from grey-brown to bluish, whilst on the ventral ones it is of clear colour. Not too aggressive animal, if disturbed it can, with the sting of its tail, inflict severe wounds, even deadly.

The Roughtail stingray Dasyatis centroura Mitchill, 1815), is a species that on average exceeds the length of 2 m and that characterizes for the presence of various spiny tubercles on the back and along the tail.

The tail is very robust and is provided of one or more serrated and venomous stings. The colouration on the back takes on colours varying from grey-black to brownish, whilst the ventral is usually whitish. Diffused in the subtropical and tropical seas of both sides of the Atlantic Ocean, the Roughtail stingray is reported also in the Mediterranean, including the Italian waters.

The Common stingray (Dasyatis pastinaca Linnaeus, 1758), is a species amply diffused in the waters of the northern Atlantic, from the Canary Islands up to Norway and the Baltic Sea, as well as in the Mediterranean and Black Sea ones. It is a cartilaginous fish that may reach the length of 2,5 m and one and a half metre of breadth, with muzzle and rather small eyes placed in front to two spiracles. The body is usually of grey-brownish colour on the dorsal parts, clear in the ventral ones. It preferably lives on the sandy and muddy seabeds, where it gets shelter and food.

Like the other species of the genus, the Common stingray has the tail armed with a robust serrated and veneniferous sting with which it can cause even deadly wounds.

In all world temperate and subtropical waters, where it preferably leads a pelagic life off the continental shelf, lives the Pelagic stingray (Pteroplatytrygon violacea Bonaparte, 1832). Known also as Violet stingray, it is a fish that characterizes for having the eyes that, unlike the other stingrays, are not protruding. The dimensions of the Pelagic stingray are around 150 cm of length, tail included, and 80 cm of breadth. The tail, long and similar to a whip, is armed with one or two venomous stings. The colouration of the body varies from grey-violet to light blue-greenish on the dorsal parts, whitish in the ventral ones.

Several specialists ascribe to a genus of its own (Himantura Müller and Henle 1837) species of Myliobatiformes that distinguish from the other stingrays because having a long and thin tail devoid of pinnulae.

Actually, the taxonomy of the species presently attributed to this group, most of them native to western Pacific and to the Indian Ocean, is particularly uncertain as it is based on insignificant diagnostic characters. In addition, for several forms the morphological data are absolutely not sufficient for their specific attribution and therefore also for establishing their real distribution. As a consequence here we limit ourselves in furnishing mainly information of general character. Initially attributed to the genus Himantura, the Chupare stingray or Caribbean whiptail stingray (Styracura schmardae Werner, 1904) is a large stingray with a maximum breadth of the disc measuring about 2 m.

The tail has only one serrated dorsal spine that is implanted in the second half of the tail. Reported for the western Atlantic waters, the taxonomic validity and the actual range of this fish keep still uncertain.

The Whitespotted whipray or Sharpnose stingray (Himantura gerrardi Gray, 1851), by some specialists attributed to other genus (Maculabatis),  is a fish whose size averagely measures 2 m in length and that is met along the coastal regions, estuaries included, of the Pacific and Indian oceans. The presence of this species has been reported in the Gange River waters.

The Pale-spot whipray (Himantura alcockii Annandale, 1909) is very similar to the Whitespotted whipray, and therefore by some is considered as a synonym of the same, is actually a little known fish reported in the eastern waters of the Indian Ocean.

In the tropical Indo-Pacific waters is reported the Pink whipray (Himantura fai Jordan and Seale, 1906), species by some ascribed to the genus Pateobatis. Actually, this fish is often mistaken with other species.

Native to the great rivers the south-east of the Asian continent, the Giant freshwater stingray (Himantura chaophraya Monkolprasit and Roberts, 1990), stands among the biggest freshwter fishes as it can reach the length of 4,5 m and almost the metres of width. The body of this animal on the dorsal parts is of brown tending to grey colour and is equipped with small more or less sharp tubercles; the ventral parts are white with a characteristic black stripe along the margins.The pectoral and pelvic fins are adorned with small spots. The tail of this fish is long and thin, often more than double than the length of the disc; the poisonous spine is the longest among those of the other stingrays and may measure even 40 cm.

And more, always to the same genus are attributed the following species. The Ganges whip ray (Himantura fluviatilis Hamilton, 1822), mentioned only for the Ganges River and of which we have very few information, the Whitetail stingray (Himantura granulata Macleay, 1883), is found in the tropical waters of the Indian and Pacific oceans up to the northern coasts of the Australian continent.

The Reticulate whipray (Himantura uarnak Gmelin, 1789)  has rhomboid-shaped body, even more than 120 cm broad. The tail, shaped like a whip, over three times longer than the body, like the other species of the order, is armed with a poisonous sting close to the base. The dorsal parts in the adults are yellow-brownish with a grid of dark and bordered of light spots; the ventral ones are uniformely clear. Amply diffused in the Pacific and Indian Oceans and in the Red Sea from where through the Suez Canal has recently reached the eastern Mediterranean waters.

Moreover among the members of the Myliobatifomes ascribed to other genera, are reported the Kuhl’s maskray (Neotrygon kuhlii Müller and Henle, 1841), fish whose overall length rarely exceeds the 40 cm and with the grey-green or yellowish back adorned with oval spots of electric blue colour. The tail of the Kuhl’s maskray is long and thin with white extremity and is armed with one or more poisonous stings. It is frequently found in the tropical waters of the Indian and Pacific Oceans.

The Cowtail stingray (Pastinachus sephen Forsskål, 1775) is a big fish that in the adults can reach the length of 3 m and 250 kg of weight. The colouration of the body is uniform, brownish on the back, white ventrally. Characteristic distinctive of this species is a long skin fold place under the tail that in its middle bears a poisonous sting. The species is reported for the tropical waters of the Indian and Pacific oceans and of the Red Sea.

The Bluespotted ribbontail ray (Taeniura lymma Forsskål, 1775), called also Blue-spotted ray, is a species living in the waters of the Indian and Pacific oceans up to the Red Sea. It is a medium-sized fish that rarely exceeds the 70 cm in length.

On the back the body has a colouration varying from pinkish to yellow-greenish and is adorned by evident electric blue oval spots, hence the common name. The belly is white-blue. The tail has in its extremity one or two venomous stings.

The Black-spotted stingray (Taeniura meyeni Müller and Henle, 1841)  is a fish owing its name to the fact of presenting the back, of dark grey colour, marked by numerous black spots. The central parts are white.

The tail is long and has at the base one or more venomous stings. Big-sized animal, the adult specimens can reach the 3 m of length and the 150 kg of weight, is rather common on the shallow sandy seabeds of the tropical waters of the Indian and Pacific oceans and of the Red Sea. The Round ribbontail ray (Taeniura melanospilos  Bleeker, 1853) is considered synonym to Taeniura meyeni.

The Porcupine ray (Urogymnus asperrimus Bloch and Schneider, 1801) owes its common name to the numerous spiny tubercles located on the dorsal surface of the body. The tail of the Porcupine ray is very thin and, unlike the other stingrays, does not have the venomous sting. This is an about 2 m long fish, presently reported in the tropical waters of the eastern Atlantic ocean and of the Indian and Pacific ones up to the Philippines, Indonesia, New Guinea and Australia.

The Common eagle ray (Myliobatis aquila Linnaeus, 1758) is a fish with a body long up to 1,5 m and 2,5 m broad, that present the classic discoidal shape of the rays, more enlarged laterally.

Like the Rays it has two very ample lateral and pointed lateral fins, slightly arcuate, whose shape recalls falciform wings (hence the scientific name). The tail, shaped like a whip, is more than twice as long as the body and is armed with a dorsal spine having a venom gland. The skin is smooth and is covered by mucus that renders it particularly skiddy.

It is found in the temperate waters of the northern Atlantic and of Mediterranean, where is particularly common in the Adriatic Sea. It preferably lives in shallow waters, often not far from the surface.

The Bull ray (Pteromylaeus bovinus G. Saint-Hilaire1817), in Italian called also Vaccarella or Colombo di mare, is a Myliobatiformes similar in appearance to the Common eagle ray from which differs at first sight as having big and prominent head, with a more marked and sharp snout. The body is depressed and in the adult specimens appears of colour varying from pale brown to brown-greenish on the dorsal parts and white on the ventral ones. The young are characterized by 7/8 dorsal stripes that disappear when they reach the maturity. The tail, very long and filiform, has at the base a small dorsal fin armed with a robust venomous sting.

The Bull ray has a vast diffusion that includes the eastern Atlantic Ocean, the south-western Indian Ocean, the Mediterranean and the Black Sea; it is reported also in the Atlantic but its presence is to be defined. It prefers the seabeds of the temperate and tropical waters, including those of lagoons and river estuaries.

The Pacific white-spotted eagle ray (Aetobatus laticeps Gill, 1865), diffused in the eastern Pacific Ocean tropical waters, and the Whitespotted eagle ray (Aetobatus narinari Euphrasén, 1790), limited to the Atlantic, differ from each other genetically, but are hardly distinguishable from the morphological point of view and both present the dark body adorned with white spots.

Other species of the genus that may be met in the western tropical waters of the Indian and Pacific oceans is the Ocellated eagle ray, called also Whitespotted eagle ray (Aetobatus ocellatus  Kuhl, 1823). It is a big fish, it can reach even the length of 3 m, that characterizes for the dorsal parts that are of darck greenish colour, with whitish spots, rarely ocellated.

In the tropical and subtropical waters of the Pacific and Indian oceans and, rarely, also in the eastern Atlantic, lives the Inshore manta ray (Mobula alfredi (Krefft, 1868)  that, with an average length between 3 and 3,5 m is one of the biggest rays.

The Smoothtail mobula (Mobula munkiana Notarbartolo di Sciara, 1887) is found in the warm tropical waters of eastern Pacific. Known also with the name of Munk’s devil ray, it is a species that normally reaches a breadth of about 1 m, with the tail long and thin and spineless.

With a disc opening that exceeds the 6 m of width and a weight of more than 1 ton, the Giant manta (Mobula birostris Walbaum, 1792) is undoubtedly the giant of the Myliobatidae.

In addition to its impressive size, the species, by some attributed to the genus Mobula, characterizes for having a very large mouth with on the sides two very mobile typical appendages, called cephalic fins, that while swimming are kept rolled assuming the appearance of horns, hence the specific name. The tail is thin, barely exceeds the length of the body and presents only rudiments of poison stings. The dorsal fin is small.

Present in all seas and oceans of the tropical and temperate belt, this species has not been reported for the Mediterranean Sea. Of essentially pelagic habits, the Giant manta lives alone or united in schools that at times may become very numerous.

Excellent swimmers, these fishes are able to perform even spectacular leaps out the water, probably with the purpose of getting rid of the parasites.

The Giant manta eats mainly zooplankton it catches swimming and conveying the water towards the mouth with the help of the two cephalic fins that are kept open.

The Pacific cownose ray, called also Golden cownose ray or Pacific cow-nose ray (Rhinoptera steindachneri Evermann & Jenkins, 1891) is a species reported for the shallow waters, estuaries and coastal swamps of eastern Pacific. About one metre in size, it preferably lives on soft seabeds, close to rocky or coral reefs, where it nourishes of crustaceans and benthic mollusks. occasionally, it gets up to the surface and may even leap out of water.

Among the most common species of the order Myliobatiformes of the coastal waters of eastern Australia we mention the Common stingaree (Trygonoptera testacea Müller & Henle, 1841). This is a small fish, usually around the 50 cm of length, that characterizes for the caudal fin and the shape of a leaf. It preferably lives on sandy seabeds, rocky cliffs and estuaries.

The Bull’s-eye stingray (Urobatis concentricus Osburn & Nichols, 1916), known also as Spot-on-Spot round ray or Reef stingray, is a small species, about 50 cm, reported for the coastal waters of central-eastern Pacific. It preferably lives in shallow waters, estuaries and coastal lagoons where it feeds on worms, crustaceans and small fishes.

The Yellow stingray (Urobatis jamaicensis Cuvier, 1816 ) is a species reported in the tropical waters of Atlantic, from North Carolina to Trinidad Island. It lives on the sandy, muddy or weedy seabeds near coral reefs. Like the other congeneric species, this fish has a size of about 35 cm, with short tail and well developed caudal fin. In the coastal waters of central-eastern Pacific, from California to Mexico, lives the Spotted round ray

(Urobatis maculatus Garman, 1913) small species (about 40 cm) of the Myliobatiformes. Of diurnal habits, it is met preferably on shallow sandy and muddy seabeds where it nourishes of worms and small crustaceans.

The Leopard round stingray (Urobatis pardalis Del Moral-Flores, Angula, López & Bussing,2015)  is a small fish, just under 50 cm, who owes its specific name to the spotted livery of the back that recalls the fur of a leopard. Known also with the names of Central American round stingray or Costa Rican round stingray, it is a ray living in the shallow waters of eastern Pacific, from Costa Rica to Colombia.

Subclass HOLOCEPHALI

They are considered a subclass of Cartilaginous fishes (Chondrichthyes)  where are comprised species that characterize already at first sight due to the remarkable dimensions of the head, prominent on those of the rest of the body, hence the name of the taxon, that literally means “all head”. The snout of these singular fishes is rounded, often rostrum forged or with the extremity equipped with a hook-like appendage. In the species of Callorhynchidae, the snout elongates in a sort of proboscis provided of a big very mobile fleshy lobe, that probably is utilized for digging into the bottom.

Other characteristics distinctive of these fishes is the presence on each side of four gills very close together and located inside a gill chamber operculated by a skin fold. The gills communicate with the outside by means of a single opening placed on the sides of the head, just anterior to the pectoral fins.

The mouth is small, with the mandible joined to the cranial case and equipped with two pairs of plates suitable for grinding, coming from the transformation of the primary set of teeth. conversely, the jaw has only one couple of grinding plates. The dorsal cartilaginous chord is not fractionated in the vertebral bodies and keeps only the functions of support axes.

The pectoral fins of the Holocephali are very big and, considering that the tail is very thin and of modest size, they represent the only propulsion organ in swimming.

Of the two dorsal fins, the first, very  high and located just behind the head, is preceded by a long and robust poison sting, whilst the second is low and fringed and continues with the caudal fin. Usually, the tail is of gephyrocercal type, that is where the first caudal fin is reduced and atrophied and is replaced by a secondary fin formed by posterior extensions of the dorsal and the anal fins.

In the Holocephali the two sexes are well differentiated. The males are always smaller than the females and, like in most Cartilaginous fishes, are equipped with a copulatory organ coming from the pelvic fins (missipterygius or pterygopodia). Moreover, in the upper part of the snout the males of the Chimerae are provided of a long and clavate appendage (clasper), usually toothed, with which they stick to the female while mating.

And still, the males of the Rhinochimaeridae, who together with Chimaeridae and Callorhynchidae represent the three families ascribed to the subclass, have anterior to the pectoral fins also a couple of prehensile appendages also utilized for clinging to females while copulating. Oviparous animals, the females lay only two eggs each time enclosed in a densely perforated rigid capsula for allowing the change of oxygenated water necessary for the develpment of the embryo.

Pelagic animals, these fishes are found in the temperate seas of the boreal hemisphere where they love the cold and deep waters.

The present Holocephali are represented only by the order of the Chimaeriformes  to which are ascribed altogether 25 species. Among the most known species, following are to be cited.

The Rabbit fish (Chimaera monstruosa Linnaeus, 1758)  is a Chimaeridae diffused in the Atlantic Ocean and also in the Mediterranean. It is a species with an unmistakable look that recalls that of a rabbit. The eyes are big, suitable for the vision in great depth and the snout is rounded with small mouth. It is present only one gill slit per side. The first dorsal fin is high and has one well developed poison sting. Usually the size varies from 1 to 1,5 m. It nourishes of invertebrates and small fishes, mainly herrings.

Another species of the Chimaeridae is the Elephant fish (Hydrolagus colliei Lay and Bennett, 1839)  found along the Pacific north-eastern coasts, preferably on sandy, muddy or rocky bottoms.

To the Rhinochimaeridae belongs the Pacific longnose chimaera or Rat fish (Harriotta raleighana Goode and TH Bean, 1895), species populating the northern waters of the Atlantic up to those of western Africa where it reaches depths even exceeding the 3000 m.

In the coastal waters off Namibia and South Africa, at depths exceeding even 350 m, is diffused the Cape Callorhynchus (Callorhynchus capensis Linnaeus 1758), species of Callorhynchidae whose dimensions usually may reach 120 cm. Indicated also with the names of Cape elephantfish or St. Joseph or Joseph, the Cape elephantfish nourishes of worms, mollusks and small fishes.

To the same family of the Callorhynchidae is attributed the Australian ghostshark (Callorhinchus milii  Bory de Saint-Vincent, 1823) medium sized fish, usually about 80-120 cm of length, that distinguishes for the protruding snout with the extremity formed like a club, due to the eyes remarkably developed and place up and for the presence of a venomous dorsal spine planted just before teh dorsal fin. It lives in the waters of the south-western Pacific, in southern Australia and in New Zealand.

 

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