(from Gibson, R. (1981). Nemerteans of the Great Barrier Reef. 3. Heteronemertea (Lineidae).. Zool. J. Linn. Soc.. 171-235.)

Heteronemertea with a single pair of horizontal lateral cephalic slits; proboscis simple, unbranched, containing three muscle layers (outer circular, middle longitudinal, inner circular) and one muscle cross; rhynchocoel circular musculature not interwoven with body wall muscle layers; dorsal fibrous core of cerebral ganglia branched into upper and lower bifurcations only at rear; nervous system with neither neurochords nor neurochord cells; foregut with circular splanchnic musculature but no subepithelial gland cell layer; longitudinal muscle plate present between rhynchocoel and foregut; dermis well developed but glands not separated from outer longitudinal muscle layer of body wall by connective tissue stratum; blood system with cephalic lacuna, foregut vascular plexus and three longitudinal vessels in intestinal region which do not possess transverse connectives; excretory system restricted to region near foregut-intestine junction; cephalic glands extensively developed but entirely pre-cerebral; tripartite frontal organ present; eyes far anterior, rudimentary; sexes probably separate.