prostomium

thumb|upright=1.5|Augenerilepidonotus|Augenerilepidonotus dictyolepis specimen from Museums Victoria showing the prostomium with notable structures labelled

The prostomium (From Ancient Greek, meaning "before the mouth"; : 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 prostomium together with the peristomium, which includes the mouth and pharynx, make up the annelid head. thumb|upright=0.7|Scanning electron micrograph of a newly hatched European nightcrawler Dendrobaena hortensis|(Dendrobaena hortensis) showing the prostomium