Author: Blainville, 1816
Field Marks:
Short-nosed, cylindrical sharks with no anal fin, 2 dorsal fins with or without spines, the first with origin in front of pelvic origins, and small to moderately large denticles.
Diagnostic Features:
Trunk stout to slender but not markedly compressed, with or without low abdominal ridges. Head conical to moderately depressed; last (5th) gill slits may be enlarged but not abruptly expanded from first 4 gill slits; spiracles moderately large to very large, close behind eyes; nostrils usually well apart from each other, separated by a space their width or more; mouth arched or transverse, with short, moderately long, or very long labial furrows that may virtually encircle the mouth; lips usually not expanded and papillose, except for a few dalatiine genera; teeth highly variable, with a cusp always present and cusplets variably present or absent, not bladelike and similar in both jaws, bladelike and more or less similar in both jaws, or bladelike in the lower jaw only and highly divergent in shape from the acute needlelike upper teeth, but never bladelike and with cusplets in both jaws. Two small to rnoderately large dorsal fins, the first variably smaller or larger than the pelvic fins, with its base at least partly anterior to the pelvic origins and usually well anterior to them; caudal fin with or without a subterminal notch.
Habitat, Distribution and Biology:
The dogfish shark include a great variety of small to gigantic sharks, with their greatest diversity in deep water. The Squalidae has a vast geographic and bathymetric range, perhaps greater than any other family or sharks, in all seas from the Arctic to the sub-Antarctic. Most genera and species are found on or near the bottom on the temperate to tropical continental and insular slopes down to at least 3675 m; unidentified members of the genus Centrophorus have been seen from a bathyscaphe on the ocean floor at over 6000 m depth. A number of highly diverse small temperate and tropical dogfishes are oceanic and epipelagic, mesopelagic and probably bathypelagic, in some cases making diel vertical migrations that may take them from near the surface to the ocean floor. Among these are some of the smallest of living sharks, of the genera Squaliolus and Euprotomicrus, that mature at less than 20 cm long. In contrast are two gigantic sleeper sharks in the genus Somniosus, attaining a size over 6 m, that are slope-epibenthic sharks in temperate waters but range to the surface and the intertidal in boreal and Arctic waters. Several species of the genus Squalus are common on the continental and insular shelves; they may range close inshore in cool temperate waters but are usually epibenthic and well offshore in the tropics, where they may be displaced from inshore habitats by members of the families Carcharhinidae, Sphyrnidae, and other carcharhinoid families.
Some dogfish sharks are solitary, but some species form immense schools that are highly nomadic, moving locally and on regular yearly migrations. All members of this family in which reproduction is known are ovoviviparous (aplacental viviparous), having one or two to over 20 young in a litter. Dogfish feed on a wide variety of prey, chiefly bony fishes but also other sharks, cephalopods, crustacea, other invertebrates, and even marine mammals. Among the dogfishes are the only known chondrichthyian parasites, 'cookie-cutter' sharks of the genus Isistius, that eat mesopelagic fishes and squid but are specialized to attach themselves by suctorial lips to the sides of large bony fishes, ceataceans and sharks, and cut out plugs of flesh. Several species apparently feed communally, and may locally exhaust or drive away prey species; Many species have powerful lower cutting dentitions and can dismember large prey. Schools of at least one deepsea lanternshark (Etmopterus virens) may attack prey cooperatively, killing deepwater squid too large for an individual shark to overcome. None of the dogfish sharks are very dangerous to people; some species use their mildly toxic finspines or sharp teeth as weapons when captured and can inflict punctures or lacerations on unwary fishermen. None of these sharks have been recently involved in unprovoked attacks on people; there are old, unverified stories of sleeper sharks attacking people in kiyaks, however.
Interest to Fisheries:
Species of Squalus are taken in large quantities for human consumption and other purposes, but other species, particularly Centrophorus, Centroscymnus, Dalatias, Deania, Scymnodon, and Somniosus, are utilized also. Deepwater species yield liver oil and are processed for fishmeal.
Remarks:
The account of Squalidae presented here follows the reviews of Bigelow and Schroeder (1957) and Bass, d'Aubrey and Kistnasamy (1976). Many writers separate the genera Dalatias, Euprotomicroides, Euprotomicrus, Heteroscymnoides, Isistius, Scymnodalatias, Somniosus, and Squaliolus in the family Dalatiidae, and separate the Squalidae from the Dalatiidae by the presence of fin spines on both dorsals of the former family. As noted by Hubbs and McHugh (1951), loss of fin spines has probably occurred more than once among squaloids, and grouping squaloids by presence or absence of spines produces heterogeneous, polyphyletic groups. Preliminary work on squaloid morphology led me to group the squaloids other than Echinorhinus in a single family, Squalidae, with five subfamilies (Compagno, 1973c): Etmopterinae for Aculeola, Centroscyllium and Etmopterus; Squalinae for Centrophorus, Cirrhigaleus and Squalus; Deaniinae for Deania;.Oxynotinae for Oxynotus; Somniosinae for Centroscymnus, possibly Enchiridiodon (later synonymized with Centrophorus by Bass, d'Aubrey and Kistnasamy (1976), Scymnodon and Somniosus; and Dalatiinae for Dalatias, Euprotomicroides, Euprotomicrus, possibly Heteroscymnoides, Isistius, Scymnodalatias, and Squaliolus. Further work indicates that Deania is closely related to Centrophorus and should be included in the Squalinae; Oxynotus is close to the genera placed in Somniosinae and should share a common group with them; that Scymnodalatias should be removed from the Dalatiinae and placed in the common group for Somniosinae and Oxynotinae; and that the Dalatiinae as restricted to Dalatias, Euprotomicroides, Euprotomicrus, Heteroscymnoides, Isistius and Squaliolus forms a compact if morphologically varied group of highly derived sharks. Pending completion and publication of my work on squaloid morphology I prefer to include the squaloid genera other than Echinorhinus and Oxynotus in a single family, Squalidae, without subdivision, and retain the family Oxynotidae for Oxynotus following common current practice (Bigelow and Schroeder, 1957, Bass, d'Aubrey and Kistnasamy, 1976).
Papers by Yano and Tanaka (1983, 1984, 1984a) clarify the status of Scymnodon and Centroscymnus from the western Pacific. Centroscymnus coelolepis is reported from Japan, Scymnodon obscurus from the Atlantic is synonymized on good evidence with the Pacific S. squamulosus, and a new species, S. ichiharai, is described from Japan. S. ichiharai is undoubtedly valid but further bridges the gap between Scymnodon and Centroscymnus, and makes it likely that the two genera will have to be synonymized.