Читать книгу Clinical Guide to Fish Medicine - Группа авторов - Страница 77

This is the largest order of sharks. There are two dorsal fins in most and an anal fin, five gill slits, a nictitating membrane, and the mouth extends behind the eyes. They can be oviparous, ovoviviparous, or viviparous. Relevant families include the requiem sharks (Carcharhinidae), catsharks (Scyliorhinidae), hound sharks (Triakidae), and hammerhead and bonnethead sharks (Sphyrnidae).

Requiem sharks look like the “typical shark”. There is an internal nictitans and spiracles are absent. The intestine has a scroll valve. Catsharks have rudimentary nictitans, small spiracles, and a spiral valve. Hound sharks have spiracles and a spiral valve. The hammerheads and bonnetheads have lateral extensions to their heads (cephalofoil) with eyes perched on the lateral aspects. Spiracles are absent and they have a spiral valve (Nelson et al. 2016).