by J. Badcock
Deepwater fishes, medium-sized or small (to 276 mm in area, but often about 50 mm and males sometimes less); body usually elongate, mouth large, upper jaw long, reaching back well behind eye; fine teeth, uniserial on premaxillae (except in Triplophos), anteriorly biserial on dentary; branchiostegal rays 12-17, 4-6 on epihyal; gillrakers well developed. Dorsal fin at or behind midpoint of body (rarely in front), anal fin more or less opposite but base longer, sometimes almost to tail; small adipose dorsal fin present in some species. Swimbladder capacious, or regressed. Scales present or absent.
Photophores usually present, discrete, not sharing photogenic masses (but sometimes obsolete or absent): BR photophores 7 13; isthmus with or without photophores; single ORB photophore; one or two series of photophores before pelvic fins (OA and IV plus VAV) and a series behind (AC), but no photophores on head and body in some species (e.g. Cyclothone obscura).
Generally oceanic, some pseudoceanic, juveniles and adults at about 200-3,000 m by day, pre-metamorphic larvae near surface; some are diel vertical migrants, others partial or non-migrants; post-larvae sink slowly or rapidly after metamorphosis; populations stratified by size with depth during day, the smaller individuals at shallower depths. Common. Feeding on zooplankton. Most are dioecious, but some protandrous hermaphrodites; breeding season often varies with latitude; post-larval photophore development slow (with OP 3 developing first) or rapid (most ventral photophores developing simultaneously).
Genera 6; in Clofnam area 5.
Recent revisions; Weitzman (1974).