The Echinorhinidae, placed in this order in Nelson (1994), is now placed in its own order following de Carvalho (1996). Three of the families now recognized were regarded as subfamilies of Dalatiidae in Nelson (1994) (see Dalatiidae).
Six families, 24 genera, and at least 97 species.
Family SQUALIDAE (34)—dogfish sharks. Marine, cool temperate to tropical, cir-cumglobal on continental and insular shelves and slopes and on sea mounts; Atlantic, Indian, and Pacific.
Both dorsal fins with spines and spines not grooved; teeth on lower jaw not much larger than those on upper jaw; upper precaudal pit usually present; caudal peduncle with a pair of lateral keels.
The Spiny Dogfish, Squalus acanthias, is one of the most cosmopolitan fish species, being widespread in the Northern and Southern Hemispheres but virtually absent in tropical waters and the Indian Ocean. This family was placed in its own order, Squaliformes, in Shirai (1992a, 1996) and regarded as the sister group to all remaining euselachians.
Two genera, Cirrhigaleus (2) and Squalus (8, and six undescibed species), with at least 10 species (Compagno, 2005).
Family CENTROPHORIDAE (35)—gulper sharks. Marine, warm temperate to tropical, continental and insular outer shelves and slopes; Atlantic, Indian, and Pacific (absent in eastern Pacific).
Both dorsal fins with spines and both spines grooved; teeth on lower jaw larger than those on upper jaw; precaudal pits and lateral keels absent on caudal peduncle.
Two genera, Centrophorus (10) and Deania (4), with 14 species (Compagno, 1999, 2005).
Family ETMOPTERIDAE (36)—lantern sharks. Marine, tropical to temperate, continental and insular slopes (rarely on shelves), a few oceanic; parts of the Atlantic (extending north to Iceland), Indian, and Pacific.
Both dorsal fins with spines and both spines grooved; caudal fin with subterminal notch; luminous organs usually present on body. These are small sharks, the maximum length is under 90 cm in most species.
Five genera, Aculeola (1), Centroscyllium (7), Etmopterus (31, with three unde-scribed species), Miroscyllium (1), and Trigonognathus (1), with 41 species (Shirai, 1992a; Shirai and Okamura, 1992; Compagno, 1999, 2005).
Family SOMNIOSIDAE (37)—sleeper sharks. Marine, Arctic to sub-Antarctic, continental and insular slopes (on shelves in Arctic and sub-Antarctic), some oceanic; Atlantic, Indian, and Pacific.
Dorsal fins usually without spines (present in a few species but small and in both fins); lateral ridge present on abdomen between pectoral and pelvic fins; luminous organs present in most.
Seven genera, Centroscymnus (2), Centroselachus (1), Proscymnodon (2), Scymnodalatias (4), Scymnodon (1), Somniosus (including Rhinoscymnus, 5), and Zameus (2), with 17 species (Compagno, 2005). Somniosus is in both the Arctic and sub-Antarctic and extends onto inner shelves.
Family OXYNOTIDAE (38)—rough sharks. Marine, continental and insular shelves and slopes; eastern Atlantic (including Mediterranean), western Atlantic, and western Pacific.
Body very high and compressed, triangular in cross section; dorsal fins very high, each with a large spine that may be concealed by the fin; origin of first dorsal fin may extend far forward over gill openings; lateral ridge present on abdomen between pectoral and pelvic fins; skin very rough; luminous organs present.
One genus, Oxynotus, with five species (Compagno, 2005).
Family DALATIIDAE (39)—kitefin sharks. Marine, tropical to temperate, continental and insular shelves and slopes and oceanic; Atlantic, Indian, and Pacific.
Dorsal fins without spines, except species of Squaliolus have a spine in the first dorsal fin; luminous organs present, appearing as black dots mainly on ventral surface (Shirai, 1992a).
One species of this group, Squaliolus laticaudus, and the proscylliid Eridacnis radcliffei are the smallest known sharks, reaching only about 25 cm in total length (Compagno, 1984a, b). The small and pelagic cookiecutter sharks of the genus Isistius, with modifications to their feeding apparatus, cause craterlike wounds in other fishes and cetaceans (Shirai and Nakaya, 1992).
In Nelson (1994), the Etmopteridae, Somniosidae, and Oxynotidae were recognized as subfamilies of the Dalatiidae.
Seven genera, Dalatias (1), Euprotomicroides (1), Euprotomicrus (1), Heteroscymnoides (1), Isistius (perhaps 3, cookiecutter sharks), Mollisquama (1), and Squaliolus (2), with about 10 species (Compagno, 2005).
fOrder PROTOSPINACIFORMES. One family, Protospinasidae, with one genus, Protospinax, Upper Jurassic, Bavaria. The position of this fossil was resolved by de Carvalho and Maisey (1996) based on new material and cladis-tic analysis. Their re-evaluation was based on a revised data matrix, largely from Shirai (1992a), with some differing interpretations of Shirai's characters. Their study supported Shirai's hypnosqualean group and they formally recognized the group as the Superorder Hypnosqualea, with Protospinax as sister to the living hypnosqualeans (i.e., all remaing neoselachians in the present classification). Although this phylogeny is not followed here, Protospinax is regarded as sister to the remaining squalomorphs, the squatinids and pristiophorids.
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