Polychaeta

A loose definition of members of this class is: marine aclitellate annelids usually bearing numerous chaetae emanating from parapodia (outgrowths on each segment). They are a diverse and specious group found mostly in the marine environment (although there are freshwater and terrestrial species). Within soft sediment environments, they are among the most dominant and species rich taxa. This makes them ecologically important and ideal organisms for environmental assessment because, in addition to their abundance and diversity, they are generally quite small and relatively sessile giving clues to the biotic response to environmental change.

An online key to the families can be found at Taxonomy across the Internet site