Author: Gill, 1862
Field Marks:
Usually elongated, catlike eyes with nictitating eyelids; nostrils usually without nasoral grooves but, when present, these are broad and shallow; mouth long, arched and reaching past anterior ends of eyes; small cuspidate teeth. Two small, spineless dorsal fins and an anal fin, the first dorsal base over or behind pelvic bases, no precaudal pits, and the caudal fin without a strong ventral lobe ar lateral undulations on its dorsal margin.
Diagnostic Features:
Head without laterally expanded blades; eyes elongated and fusiform, oval, or slitlike, their length over 1.5 times the height; nictitating eyelids rudimentary; spiracles present and moderately large; anterior nasal flaps variably shaped, but not barbel-like, except for one genus (Poroderma) with a barbel formed from a separate ridge on each anterior nasal flap; internarial width about 0.6 to 1.3 times nostril width; labial furrows absent or very short to very long; teeth small, with acute narrow cusps, often lateral cusplets, and basal ledges, not bladelike, and similar in both jaws; posterior teeth comblike or not; tooth rows 40 to 101/34 to 111. Precaudal pits absent. First dorsal fin small and not keel-like, much shorter than caudal fin; first dorsal base over or behind pelvic bases, its origin either slightly ahead of pelvic origins (Cephalurus) or well behind them; midpoint of first dorsal base always posterior to pelvic origins; pectoral fins with radials confined to bases of fins; ventral caudal lobe absent or very weak; no undulations or ripples in dorsal caudal margin. Neurocranium with or without a supraorbital crest. Vertebral centra with or without strong, wedge-shaped intermedial calcifications. Valvular intestine with a spiral valve of 5 to 21 turns. Many species with variegated colour patterns, some without them. Development usually oviparous, but some species ovoviviparous.
Habitat, Distribution and Biology:
This is by far the largest family of sharks, with a broad worldwide geographic range in tropical to cold-temperate and arctic waters; catsharks occur from the intertidal zone to the edges of the continental and insular shelves and down the slopes to depths greater than 2000 m. Catsharks are generally found on or near the bottom in coastal waters inshore and offshore; none are oceanic, although some deepwater species may range a considerable distance off the bottom. Most species are small, less than 80 cm long, and while some may be mature at about 30 cm, a few may reach about 1.6 m length. Catsharks are generally weak swimmers and do not migrate over great distances; this is shown in their geographic distribution, which is often much more localized than that of families with strong swimming species. Some inshore species are - nocturnal, sleeping often in groups in rocky crevices in day-time and dispersing to feed at night. Many species show the primitive single oviparity, in which only one fertilized egg enters each oviduct and is deposited on the substrate at a time; the large eggs, encapsulated in tough egg-cases with corner tendrils to anchor them, have most of their embryonic development outside the mother shark and may take nearly a year to produce a hatchling shark. Others possibly in areas of intense egg predation, have multiple oviparity, in which several encased eggs remain in the oviducts for an extended period, during which time the embryos develop to advanced stages before the eggs are laid; such eggs may hatch in less than a month. Still other species have eliminated oviparity altogether and are ovoviviparous, retaining the eggs until the young are ready to be born. Catsharks feed chiefly on invertebrates and small fishes, and are harmless to people. Most species are very poorly known biologically.
Interest to Fisheries:
A minority of the species in this family are of importance to fisheries, particularly the spotted catsharks (Scyliorhinus) of the eastern Atlantic, which are much utilized for human food. Some are rather common and regularly taken as a byeatch in the trawl fisheries worldwide, and may be used for fishmeal and oil. Many are deepwater sharks, and are not known to be utilized to any great extent, although they may be a minor component of the catch of large, deep-fishing offshore trawlers. Several inshore species are commonly caught by sportfishers.
Field Marks:
The present arrangement of this family follows the revision of the Scyliorhinidae by Springer (1979) in most details.
Fowler (1941) placed the dubious genus Caninoa Nardo, 1841, with Thalassokephetes Gistel, 1848 a junior synonym, in the family Scyliorhinidae, on the possibility that it may be a one-dorsaled catshark like Pentanchus profundicolus. I follow Tortonese (1952) in considering Caninoa and its single species C. chiereghini dubious and possibly mythical shark taxa, that are not placeable in modern shark families.
Smith and Radcliffe (1912) proposed a new family for their new genus and species of one dorsal-finned shark, Pentanchus profundicolus, on the assumption that the species was a hexanchoid with five gill openings. However, Regan (1912), Garman (1913), and subsequent writers noted that Pentanchus profundicolus was a scyliorhinid, the genus Pentanchus was close to Apristurus or a senior synonym of it, and that the Pentanchidae was a junior synonym of the Scyliorhinidae.
The following nomina nuda, named by Blainville (1816) and placed in his subgenus Scyliorhinus (Genus Squalus) may refer either to scyliorhinids or orectoloboids: Squalus myops, S. breviculus, S. punctatus, S. punctulatus, S. unicolor, S. variegatus, S. lambarda.