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Squalidae (dogfish; subclass Elasmobranchii, order Squaliformes) A fairly large family of marine sharks that have two dorsal fins, each often preceded by a solid spine. The anal fin is lacking. Some species, e.g. Etmopterus spinax (Atlantic velvet belly), 90 cm, are relatively small, while others, e.g. Somniosus microcephalus (Greenland shark), may reach a length of about 6.4 m. All members of the family are live-bearing species which often travel in large schools. There are at least 61 species, distributed world-wide.