By Hiroyuki Motomura

Onuxodon parvibranchium

Small to medium-sized fishes, rarely reaching 50 cm TL. Body elongate and compressed or subcylindrical. Eye diameter subequal to snout length in adults. Supramaxilla absent. Mouth terminal, often with strong teeth. No spines on opercle. Scapula and coracoid fused; upper distal radial of pectoral fins enlarged; hyomandibula with large foramen. Dorsal and anal fins long, connected to caudal fin; dorsal fin rays shorter than opposing anal fin rays; highly modified first dorsal fin ray in larvae. Pelvic fin with a soft ray, or without ray. Scales absent. Anus located below pectoral fins. Color: semitransparent to brownish.

Similar families occurring in the area. Ophidiidae: body scales present. Anus located behind posterior tip of pectoral fin.

Remarks. Occurs in shallow to moderately deep waters. Usually pelagic in larvae and benthic in adults; free-living adults in some species; commensals in body cavity of invertebrates, primarily holothurians (sea cucumbers), in most species when adults. A bycatch in some sea cucumber fisheries, but no importance to fisheries.