Hooks: 9-13; anterior teeth: none; posterior teeth: 10-16.
Maximum adult body length: 25 mm; tail: 19-24 %.
Body firm, opaque, broadest at region of tail septum; transversal musculature on trunk; head wide; hooks serrated in juveniles; one pair of very long lateral fins both on trunk and tail; lateral fins partially rayed, angular. Collarette absent; gut diverticula absent. Small eyes with crescent-shaped pigment. Seminal vesicles conical; position of seminal vesicles: touching posterior fins, close to or touching tail fin. Ovaries short; ova large. Adhesive papillae and adhesive organs absent; apical glands present.
Distribution: North-west Pacific.
Remarks: 47 specimens found at entrance of Tokyo Bay.
Type locality: 35°08'N, 139°46'E.