Scoliodon is included in Phylum-Chordata, Sub-phylum-vertebrata, super class-Pisces, Class- Elasmobranchi.
Morphology:
Scoliodon is an elongated, spindle shaped cartilaginous fish. It has laterally compressed body. A full-grown species measures from 40-60 cm in length. The body is divisible into head, trunk and tail. The head is dorsoventrally compressed and anteriorly terminates a flat snout. The trunk attains maximum thickness in the middle region and it gradually tapers posteriorly into a long tail.
The tail bears heterocercal type of caudal fin. Heterocercal means ventral hypochordal lobe is well developed than the dorsal epichrodal lobe. There are shallow pits called caudal pits at the root of the tail both on dorsal and ventral sides. These are characteristics of scoliodon. The mouth is wide crescentic aperture on the ventral side of the head. It is bounded by upper and lower jaws. Each jaw is armed teeth to catch the slippery pray. The teeth of the scoliodon are modified scales. The placoid scales cover its body and extend inside the jaw to serve as teeth.
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On each side of head is a large circular eye. Each eye is provided with movable upper and lower eyelids. The third eye lid or mictitating membrane can cover the whole eye during emergency. The pupil is a vertical slit like aperture. Two nostrils are present at the anterior part of the snout. They lead into olfactory sacs. These are exclusively olfactory in function and they have no connection with mouth cavity. Each nostril is partly covered by a small fold of skin. Posterior to eye on either side of the head are situated five vertical slits called gillslits or branchial slits. These slits lead into gill pouches and then into pharynx. Operculum or gill cover is absent.
Many pores called ampullary pores are also present on the head. These are pores of the sense organ, ampulla of Lorenzini. The cloaca opens to the anterior by a cloacal aperture, which lies between two pelvic fins. The cloacal aperture is an elongated opening. The cloacal is common chamber into which receives faecal matter, urine and gametes. On each side of the cloaea lie abdominal pores. The abdominal pores communicate the coelom to the outside. A faintline runs on either side of the body called lateral line. It is rheoreceptor (detection of water current) in function.
Fins:
The fins are thin, flat out growths of skin with muscles and are supported by cartilaginous rods or rays. The scoliodon is provided with unpaired median fins i.e. 1st dorsal fin, second dorsal fin, second dorsal fin, caudal fin, anal fin and paired fins (anterior pair pectoral fins and posterior lateral pelvic fins). The pectoral fins are large and are situated posterior to the gill clefts. The pelvic fins are simple but in males, the inner margin of the pelvic fins bear a pair of rod shaped copulatory organs called clasper or myxipterygium. The claspers are the intermittent organs that introduce sperm into female genital tract. The fins propel the body in forward direction during swimming.