Author: Osorio, 1917
Radiicephalus elongatus Osorio, 1917
Diagnosis: elongate and compressed body, general shape a tapered triangle (deep at head and narrowing to a thin caudal filament). Head short, mouth protrusible; teeth pointed, retrorse in both jaws. Dorsal fin long-based, with about 150-160 finrays, the anterior rays forming a nuchal crest; anal fin short, with 7 finrays; pectoral fin set horizontally, with 9 finrays; pelvic fins small, behind level of pectoral fins; caudal fin poorly developed, with two distinct parts. Scales absent, but epidermis shows a brickwork-like pattern; lateral line present, beginning over operculum and sloping down towards ventral profile at the anal fin, then continuing beyond caudal region onto the lower caudal fin lobe. An ink-sac in the cloaca. Colour: silvery, fins pale. Size: to 76 cm SL.
Habitat: mesopelagic; may have ability to discharge dark brown fluid from ink-sac when alarmed. Food: Iantern-fishes (Myctophidae), and possibly euphausiid crustaceans. Reproduction: no data.
Distribution: eastern North Atlantic off Morocco and the Azores. Elsewhere, off the Canaries.
Eggs, larvae and young stages. Harrisson & Palmer, 1968: 187.
Otoliths (sagitta). No data.