Idiacanthidae
by R. H. Gibbs, Jr.
Body very long, slender, without scales, its depth 20-50 times in length; skin black. Chin barbel present in females, absent in males. Dorsal fin very long, its origin before midpoint of body, with 54-80 finrays, anal fin about half as long as dorsal, with 29-55 finrays; both dorsal and anal fins ending just before tail; dorsal and anal finrays with spiny projections on each side; no dorsal adipose fin; pectoral fins absent (present in larvae);
pelvic fins present in females, absent in males. Two rows of prominent photophores on ventral part of body on each side; post-orbital luminous organ present; no pre-orbital or sub-orbital organ. Males differ greatly from females, never exceeding about 7 cm, lacking teeth, chin barbel and pelvic fins, with the post-orbital luminous organ usually longer than and up to twice the eye diameter, and a fleshy extension from the anus area
attached to the modified first anal finray. Larvae with eyes at the end of long stalks.
Fairly common in deep oceanic waters; larvae inhabiting subsurface waters, apparently descending to greater depths during or just after metamorphosis; females apparently living at 500-2,000 m during the day, migrating upward to 250 m and shallower at night; most males apparently living at 1,000-2,000 m at all times. Feeding habits poorly known, food
apparently mostly midwater fishes.
Genus 1.
Recent revisions: Novikova (1967), not entirely satisfactory; Krueger (unpublished Ph.D. thesis, 1967).