From Wikipedia, the free encyclopedia
Heteronemertea is a monophyletic order of about 500 species, containing genera such as Lineus and Cerebratulus and including the largest and most muscular nemerteans. Almost all heteronemerteans have three primary body-wall muscle strata: an outer longitudinal, a middle circular, and an inner longitudinal. The lateral nerve cords are outside the circular muscle, as in palaeonemerteans, but separated from the epidermis by the usually well-developed outer longitudinal muscle.
