; subclass Elasmobranchii, order Lamniformes)
A large family of mainly pelagic sharks, in which the last of the five gill slits are placed over the origin of the pectoral fin; the spiracle is narrow and slit-like, and the first and larger of the two dorsal fins is placed well forward. These sharks have a generally drab brown to blue colour, being lighter underneath. Some species (e.g. Prionace glauca, blue shark, which can reach a length of 3.5 m), have a world-wide distribution, avoiding only the polar seas. Galeocerda cuvieri (tiger shark) also inhabits many oceans and can reach a length of 5 m. It is live-bearing, producing up to 46 live young at a time. There are about 85 species, including species such as Mustelus mustelus (smooth hound, or dogfish), which sometimes is placed in another family (Triakidae).
Subjects: Zoology and Animal Sciences.