Prostomium (sometimes also called
acron) is the first body segment in annelids worms. 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. It sometimes bears antennae and eyes. By feeding, it often functions like a kind of overlip. The shape and composition of prostomium are important for annelid systematics.
The prostomium often also has appendages such as palps and
tentacles or cirri. Some polychaeteshave a posterior extension with sensory function on it, called caruncle. A ciliated pit or groove at the posterior end of the prostomium is another kind or sensory organ called nuchal organ (or a variety of it, the nuchal epaulette).
* [http://www.rosario.wwc.edu/inverts/Glossary/Glossary.html A glossary of invertebrate anatomy]
* [http://rmbr.nus.edu.sg/polychaete/head.html Polychaete head structures]
* [http://rmbr.nus.edu.sg/polychaete/prostomium.html The prostomium shapes of various families of polychaetes]
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