Verrill, 1892
Body very flattened, with posterior lateral margins developed as thin horizontal fins and posterior end forming a caudal fin; length up to 60 mm, width to 10 mm; rhynchocoel nearly as long as body, with wall containing separate circular and longitudinal muscle layers; 30-60 pairs of intestinal diverticula as well as 6-8 pairs of diverticula on the intestinal caecum, diverticula without ventral branches, dorsal branches much lobed; sexes dimorphic, females with 20 or more pairs of ovaries along sides of body; mature males with pair of muscular tentacles anteriorly, with compact clusters of 15-20 or more spermaries on each side of brain; colour in life flesh-pink to red, orange or bright scarlet, juveniles pale grey or colourless.
Distribution: Obtained from virtually all depths down to 3000 m or more, living at shallower depths in winter (Van der Spoel, 1985). This species has one of the widest distributions recorded for any pelagic nemertine and has been found in the North Atlantic from Cuba to southern Greenland and above both eastern and western continental slopes, through the equatorial and South Atlantic to the latitude of South Africa, in the North Pacific within a wide area off the coast of California, off Japan and the Kuril Islands, and in the Bering Sea east of Kamchatka, and in the South Pacific to 14º50'S, 85º03'W (Coe, 1954a).