Brinkmann, 1915
Body moderately slender, posteriorly with distinct caudal fin, mature males with pair of large tentacles up to about 4 mm long on the head; development of tentacles correlates with sexual maturation of the spermaries, with immature males showing only rudimentary tentacle formation; lengths of 11-19 mm, widths of < 4 mm, maximum thickness 1.25 mm; living individuals yellowish-red, with darker red alimentary tract; rhynchocoel reaching almost to posterior of body, with wall anteriorly containing separate inner circular and outer longitudinal muscle layers but with muscle layer sequence reversed behind brain; 18 proboscis nerves; stylet armature simple, with very few stylets; intestinal caecum with 3 pairs of lateral diverticula, intestine with about 60 pairs which are unbranched; females with about 25 pairs of ovaries located dorsomedially to lateral nerves; males with 5-7 spermaries situated in a single row on each side of head and reaching far behind brain to anterior base of tentacles.
Distribution: Obtained at various depths between 3500 m and the surface. Known from the North, Tropical and South Atlantic between latitudes 57ºN and 35ºS, mostly in the eastern regions of the Atlantic.