Sipunculida

a phylum or class of marine worms. The un-segmented body is 1-50 cm long. The anterior proboscis-like part of the body has a mouth and a crown of short tentacles; it is invaginable into the posterior part. The intestine is looped, and the anus is anterior and dorsal. The worm has a wide coe-lomic cavity, as many as three pairs of metanephridia (generally one pair), a rudimentary circulatory system, and a nervous system consisting of a suprapharyngeal ganglion and abdominal nerve trunk. The sexes are separate. Spiral cleavage of the egg and trochophores is characteristic.

There are about 250 species, which inhabit the soil. They are frequently found in the tubes of other worms and in the shells of mollusks. The worms feed on small animals and animal remains. In the USSR they are abundant in the Barents Sea and in the seas of the Far East.