Annelid, Polychaetes

The body of free-moving polychaetes (see figure) consists of a head, or prostomium, which may bear two or more eyes; a preoral segment, with such appendages as antennae, tentacles, and palpi (fleshy sensory projections); a trunk divisible into distinct segments; and a tail, or pygidium, which may bear anal cirri (fleshy projections) or