Prostomium vs. Peristomium — What's the Difference?

The prostomium (From Ancient Greek, meaning "before the mouth"; plural: prostomia; sometimes also called the "acron") is the cephalized first body segment in an annelid worm's body at the anterior end. It is in front of (but does not include) the mouth, being usually a small shelf- or lip-like extension over the dorsal side of the mouth.

The peristomium is the first true body segment in an annelid worm's body in the anterior end. It is directly behind the prostomium and contains the mouth, tentacular cirri, and sometimes feeding palps, which may instead occur on the prostomium.

The anterior portion of the head of an annelid worm, situated in front of the mouth.

A peristome.

(zoology) That portion of the head of an annelid situated in front of the mouth.

Same as Peristome.

That portion of the head of an annelid situated in front of the mouth.