Sipunculus

Sipunculus, a genus of worms belonging to the class Gephyrea (q.v.), and the type of the family Sipunculidae. The three main characters of the family are that the worm consists of only one segment, has no hairs or setae; and has tentacles around the mouth. A vascular circulatory system is present in most members of the family, and its structure led to the view that Sipunculus and the Gephyreans might be allied to the Holothurians or Sea-Cucumbers.