Sipunculus

Sipunculus, a genus of worms belonging to the class Gephyrea. The body is cylindrical, unsegmented, without appendages or bristles, with tentacles around the mouth. The food-canal is spirally coiled, and ends anteriorly. The sexes are separate. A common species is Sipunculus nudus, which lives in the sand on the shores of the North Sea, the Atlantic, and the Mediterranean. It measures from 6 to 10 inches in length. The animal swallows the sand for the sake of the organic matter therein contained. The members of an allied genus, Phascolosoma, often live within Gasteropod shells, narrowing and extending the mouth of the shell into a tube of cemented sand particles.