Order SQUALIFORMES: Dogfish sharks

Classification of this large and diverse group of sharks remains in a state of flux - not least as many species have such closely-overlapping characteristics that their present taxonomic positions frequently provide a source of debate. Perhaps most notable in this discussion are the familiar spiny dogfish, or spurdogs (Squalus spp.), which may contain a number of presently unnamed varieties that in many respects closely-match species already described and titled. As such, the arrangement and nomenclature followed on this website for Squaliformes - which might be termed as "traditional" in following L.J.V. Compagnošs (1984) FAO Species Catalogue - should be viewed as very liable to alter, perhaps quite radically, in the future.

The Squaloid fauna of the N.E. Atlantic region is rich. It includes one of the smallest living sharks - the spined pygmy shark Squaliolus laticaudus, attaining just over 20 cm - and one of the largest, the greenland shark Somniosus microcephalus, which may reach 6 metres. The majority of Squaloids are deepwater inhabitants, some rarely seen or caught, and consequently many aspects of their biology remain enigmatic. Some of the oceanšs more bizarre sharks are within this Order's ranks - notably the inimitable cookiecutter Isistius brasiliensis, a specialised semi-parasitic predator whose small size belies a powerful bite. Other representatives are conspicuous in their unconformist appearances - for example, the bramble shark (Echinorhinus brucus), a fascinating animal sadly in decline, and the unmistakable roughsharks (Oxynotus spp.) with sail-like dorsal fins.

Occurring worldwide, these sharks occupy a wide range of environments, both inshore and offshore, in the tropics and cold seas.  The largest of the group, the greenland shark, is restricted to boreal and Arctic/Sub-Antarctic waters where it even occurs in the most unlikely place to find a shark - beneath ice-floes. Some, such as the gulper sharks Centrophorus spp. will inhabitat depths well over 1000 metres, whilst others such as the spiny dogfish Squalus acanthias prefer the shallower environment of shelf and coastal waters, even entering the intertidal.

Field Identification Key
Ordinal Identification
Tiny to giant sharks with no anal fin. Two dorsal fins, often including a sharp spine on their leading-edges; their relative positions highly variable. Five gill slits. Body not ray-like and flattened; no saw-like extension to the snout. No nictitating eyelids. Labial furrows well-developed on both jaws.
Family Identification
First dorsal fin origin behind pelvic fin origin Skin conspicuously textured with prominent thorn-like denticles	Echinorhinidae, Bramble shark.
First dorsal fin origin ahead of pelvic fin origins
-Body noticeably high, appearing hump-backed; compressed and almost triangular in cross-section; dorsal fins conspicuously tall and sail-like; skin rough; mouth very small	Oxynotidae, Roughsharks.
-Body essentially fusiform, cylindrical in cross-section.  Dorsal fins not conspicuously tall and sail-like	Squalidae, Dogfish.