nemertini

from The Century Dictionary.

• noun A class of elongated wormlike marine animals having a ciliated ectoderm, as in the Turbellaria, and an eversible proboscis lying in a sheath on the dorsal side of the enteron. They have a mouth and an anus, simple gonads, and a vascular system; and are, as a rule, diœcious. There is no external segmentation as in the more highly organized class of Chætopoda.