by N. V. Parin
Body extremely elongate and compressed. One nostril each side of snout. Mouth large; upper jaw not protractile; lower jaw projecting. Teeth strong, fang-like in anterior part of upper jaw. Gillrakers undeveloped. Dorsal fin single, running almost entire length of body, consisting of spinous and soft portions, the former either continuous with the latter and very short (in Lepidopus and Trichiurus) or divided by notch and moderate in size (up to subequal to soft portion in Aphanopus); anal fin preceded by 2 free spines behind anus (first unconspicuous, second enlarged), its rays reduced (sometimes to entirely absent) or restricted to hinder part of fin; pectoral fins small to moderate; pelvic fins absent or vestigial, reduced to a flattened spine and 0-2 tiny rays; caudal fin either small and forked or completely absent (in Trichiurus). Scales absent. Lateral line single. No keels on caudal peduncle.
Benthopelagic on shelf, continental slope and underwater rises in 10-20 m to 1,600 m. Locally abundant. Fast-moving, active fishes; some of them shoaling; some coming closer to surface at night. Carnivorous, feeding on fishes, squids and crustaceans. Spawning throughout the year in warm waters; eggs and larvae pelagic. Valuable food fishes; Trichiurus, Lepidopus and Aphanopus are exploited commercially.
Genera 9 or 10 (see note below); in Clofnam area 4.
Recent revisions: Tucker (1956), Parin & Becker (1972 -deepsea genera (Aphanopus and Benthodesmus)).
Note. Many changes have appeared recently; several new species have been described and others are known to be described outside Clofnam area; generic system also needs revision.