Annelid Polychaetes

Annelidae (or segmented worms) is a very rich phylum composed for about 2/3 by polychaetes (marine worms).
Polychaetes, mainly benthic organisms, are the most frequent and abundant group belonging to the marine benthic communities, representing more than 1/3 of the total soft bottom benthic organisms. According to their lifestyle, they are typically divided into sedentary and   wandering organisms.
Many species crawl on the seabed or within the sediment, others have a fossorial behaviour and dig tunnels into the sand or mud. Many polychaetes live inside tubes built by themselves as single individuals or in colonial aggregations. The body of polychaetes consists of a serial repetition of segments, known as  somites. Each somite has a pair of lateral protrusions, called parapodia, provided of bristles (or chaetae). Prostomium and pygidium are respectively the head and the terminal portion of the worm. To date about 876 species of polychaetes have been identified  in the Italian Seas
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