Squalidae
by J. D. McEachran and S. Branstetter
Small to large sharks (0.15-7.3 m TL), the body sub-cylindrical, slender to moderately stout; head moderately depressed to conical, rarely greatly depressed and spatulate. Eyes without nictitating membrane. Nostrils separate from mouth. Spiracles small to large. Five gill-slits. Mouth usually short and transverse, rarely long and arc-shaped; labial fold well developed, with a deep groove (pre-oral cleft) above the corner of the mouth generally present; teeth in front of jaws similar to those at corners, tooth shape variable (but all lack basal ledges). Pectoral fins not deeply notched, triangular to brush-shaped; dorsal fin usually much before origin of pelvic fins, rarely over origin of pelvic fins. Cloaca confluent with inner margins of pelvic fins. Caudal fin moderately upturned to nearly straight, with upper lobe considerably longer than lower lobe to about equal to lower lobe. Body densely covered with small denticles, rarely body sparsely covered with large denticles which possess a central spinous point and radial ridges. Some species with luminous organs.
Generally benthic but some mesopelagic or bathypelagic. Most common at high latitudes; at lower latitudes limited to deepwater down to depths of 3,000 m. Larval development ovoviviparous. Feeding on jellyfishes, polychaetes, molluscs, crustaceans and fishes. Species range from fairly active forms which make long migrations to extremely sluggish forms; two are parasitic on large pelagic fishes and cetaceans. Several species are utilized as food, fertilizer, sources of vitamin A and leather.
Genera 16-17; in Clofnam area 11.
Recent revisions: Bigelow and Schroeder (1957).