(from Coe, W. R. (1901). Papers from the Harriman Alaska Expedition. XX. The nemerteans.. Proc. Wash. Acad. Sci.. 1-110.)
Head with deep lateral, longitudinal furrows. Proboscis usually with three muscular layers and muscular crossings.
Caudal cirrus present in perfect specimens, but often missing. Body long and flat, with thin lateral margins. Swims readily. Dorso-ventral and diagonal muscles well developed. Eyes usually absent.
Large and ribbon-like. Slaty brown to grayish green, with thin, white, lateral margins.