Chondrichthyes Write-up PDF

Habit and habitat. Scoliodon is marine but some live in estuaries and also ascend in rivers. They are active swimmers, predaceous and voracious feeders. caudal fin tail caudal second dorsal fin pit...

Habit and habitat. Scoliodon is marine but some live in estuaries and also ascend in rivers. They are active swimmers, predaceous and voracious feeders. caudal fin tail caudal second dorsal fin pit first dorsal fin lateral line eye snout anal fin or median ventral fin pelvic fin pectoral fin gill-clefts (1-5) mouth nostril extemal 11.1. Scoliodon (Lateral view). Comments: 1. Scoliodon (Fig. 11.1) is commonly called dogfish or dogshark.  2. The body is long, laterally compressed, spindle-shaped and it measures 30 to 60 cm in length and its body is divisible into head, trunk and tail. 3. The colour of the body is dark grey on the dorsal and lateral surfaces, while it is pale on the ventral surface. snout. 4. The head is strongly compressed dorso-ventrally and produced in front into a wedge-shaped Scanned with CamScanner 5. The trunk is the largest part of the body extending from behind the gill-slits up to the cloacal aperture. Tail is heterocercal with caudal fin.  6. Head bears a pair of eyes, wide ventral crescentic mouth, a pair of external nostrils and five pairs of lateral gill-clefts. 7. Trunk bears two dorsals, a caudal and a ventral or anal fins. 8. Paired fins are pectorals and pelvics. In between pelvic fins lies the cloacal aperture. 9. In male, each pelvic fin has a copulatory organ called clasper connected with its inner edge. 10. A faint line runs on either side of the body from the head to the posterior end of the tail called lateral line. 11. Shark has a food value in many countries. Its dried skin is called shagreen used for polishing furnitures and metals, etc. It is used in laboratories for dissections. Geographical distribution. Scoliodon has a wide geographical distribution; it has been recorded from Zanzibar to Sri Lanka and Sri Lanka to the Malay Archipelago in the Indian Ocean from the Bay of Bengal, the East Indies and the Philippine Islands, from Mexico to Panama in the Eastern Pacific, from Labrador to Brazil in Atlantic, from Cuba in West Indies and also off the Eastern coast of South America. Scanned with CamScanner  tail adipose fin lateral line dorsal fin eye head caudal fin anal fin pelvic fin pectroal fin gill-openings Fig. 11.4. Sphyma zygaena. Habit and habitat. Sphyrna is a common marine shark living in deep waters. It is feroceous and voracious feeder, feeds on small fishes and also attacks on man. Comments: 1. Sphyrna (Fig. 11. 4.) is commonly called hammer-headed shark. 2. Body is elongated, measuring about 4-5 metres in length and divided into head, trunk and tail. Colour of the body is greyish dorsally and yellowish on ventral side. 3. Head is flattened in front and expanded sideways into two conspicuous lateral lobes, hence, resembling a hammer. Eyes lie at the tips of lateral lobes and provided with 3 eye-lids and nictitating membrane. Mouth is crescentic and ventral, nostrils ventral at the base of lateral lobes and five pairs of lateral gill-slits. Spiracles are absent.  Scanned with CamScanner S. 4. Trunk bears median as well as paired fins. Median fins are two dorsals, caudal and an anal and paired fins are pectorals and pelvics. 5. Vertebrae are asterospondylus.  6. Viviparous, produces about 40 youngs. 7. Sphyrna is caught for its oil, although the yield is low. - Geographical distribution. Sphyrna is distributed in tropical and subtropical seas and coastal warm waters of Pacific ocean. Lower carboniferous to recent. Scanned with CamScanner  Habit and habitat. Pristis is found in warm marine waters. It often ascends in rivers. It is predaceous, feeds on fishes and other marine animals by slashing them with its saw-like minute teeth.  Scanned with CamScanner Comments: 1. Pristis (Fig. 11.8) is commonly known as saw-fish. 2. Body is shark-like, elongated, depressed and divided into head, trunk and tail. It may attain the considerable length of 3-6 metres.  3. Head and skull prolonged into a long flattened rostrum, the lateral margins of which are provided with a series of strong tooth-like denticles giving it the appearance of a saw. 4. Mouth is ventral. Spiracles are present behind the eyes on the dorsal surface of head. 5. Dorsal fins are large, the first dorsal fin is opposite to the pelvic fin. Second dorsal pin is called adipose fin. Paired fins are pectorals and pelvics. 6. Tail is well-developed and terminating in heterocercal caudal fin. 7. The fish is invaluable for liver oil of high vitamin value and skin for scale boards. Geographical distribution. Pristis is found in Mediterranean and Atlantic Oceans particularly in America, West Indies, China and Gulf of Mexico. There are two species in India, Pristis cuspidata and P. microdon, which ascend beyond tidal zones. Upper jurassic to recent. teeth rostrum or beak (saw-like) eye spiracle pectroral fin first dorsal fin pelvic fin second dorsal fin  tail caudal fin Scanned with CamScanner Habit and habitat. Torpedo or Astrape is a marine fish, found over sandy or muddy bottom at a depth of about 40 to 50 fathoms. Fish is carnivorous feeds on crustaceans and molluscs, etc. Comments: 1. Torpedo or Astrape (Fig. 11.10) is commonly called electric-ray because of the presence of a pair of electric organs over the head. 2. Body is regionated into dorso-ventrally flattened anterior subcircular dise and posterior tail. 3. The semicircular anterior margin of the disc is supported in the centre by a branched prenasal rostrum and laterally by the branched preorbital cartilages. Disc is bordered with pectoral fins. 4. Skin is smooth without scales.  5. Mouth is transverse and ventral with quadrangular naso-frontal lobe. 6. Spiracles are present behind the eyes. 7. Five pairs of gill-slits are ventral. 8. Pelvic fins are small behind the pectroals. 9. Electric organs consist of muscle fibres eye spiracle electric organ pectoral fin pelvic fin first dorsal fin second dorsal fin tail caudal fin 11.10. Torpedo or Astrape. arranged in blocks and serve as batteries. These fishes are capable of giving a heavy electric shock. 10. Tail is relatively short with two dorsal fins and a caudal fin.  11. Viviparous and produces live young ones. Geographical distribution. Torpedo is found in Mediterranean, Red Sea, Atlantic and Pacific Oceans, East Indies, China, Tasmania, Australia, Japan, South Africa, North and South America. T. marmorata is found in Indian Ocean. Upper Jurassic to Recent. Scanned with CamScanner Habit and habitat. Chimaera (Rat-fish) is a marine fish found at a depth of 350 to 2200 metres and feeds on fishes, invertebrates and seaweeds. sensory canal eye dorsal fin lateral line frontal clasper mouth operculum gill-slit pectoral fin tail caudal fin pelvic fin claspers  Fig. 11.11. Chimaera monstrosa. Comments: 1. Chimaera (Fig. 11.11) is commonly known as rat-fish or king of herrings. Body is divisible into head, trunk and tail. 2. Body is elongated and shark-like, measuring up to 1 metre in length. Head is large and compressed with a blunt conical snout. 3. Skin is naked with a characteristic open groove lodging the lateral line system. 4. Mouth and nostrils are ventral in position. 5. Gill-slits covered with non-bony operculum. Spiracles are absent. 6. Pectoral and pelvic fins are large. Ventral fin small. 7. Two large dorsal fins, anterior over the pectoral fins with a stout spine in front and posterior one is continuous and non-erectile. 8. Caudal fin consists of nearly equal-sized dorsal and ventral lobes. 9. Tail is long, tapering whip-like and diphycercal. 10. Sexual dimorphism exists. In male, head possesses a frontal clasper armed with a pad of recurved denticles, a pair of claspers present behind the pelvic fins and a pair of claspers in front of pectoral fins. 11. Eggs enclosed in egg shell. Young rat-fish is with placoid scales. Geographical distribution. Chimaera occurs off the coasts of Europe from Norway to Portugal including the Mediterranean and also in the neighbourhood of Azores, Cape of Good Hope and coasts of Japan and North America. Upper Devonian to Recent. Chimaera shows selachian and certain specialised characters. Selachian characters are cartilaginous endoskeleton, limb girdles, dermal denticles, absence of air bladder, presence of spiral valve in the intestine, conus arteriosus and clapsers in males. Specialised characters are autostylic skull, fused palatoquadrate with cranium, dental plates for crushing, and five claspers in male. Gill- slits covered with operculum, suppressed spiracles and absence of cloaca (Osteichthyes characters). Thus, Chimaera is an intermediate fish between sharks and bony fishes. Scanned with CamScanner