Worms Worms Marine worms come in many shapes and sizes. In fact there is a tendency to call any animal that is long and thin a worm, but this is a mistake. It is often quite hard to tell the difference between a beautifully coloured flat marine worm and some of the flattened, shell-less, nudibranch molluscs, which are also beautifully coloured. Marine worms are grouped into at least ten different phyla, which means that these groups are only distantly related. This is also indicates the great range of worm forms, lifestyles and habitats which occur.
Polychaetes are particularly common on and in muddy and sandy shores.
Their most obvious feature are the pairs of parapodia appendages . One pair comes from each body segment . These parapodia are used for crawling and swimming. These parapodia are often tipped with hardened spine-like setae or dorsal cirri . In some species, such as the Bristle Worm , Eurythoe complanata , these cirri may break off into your fingers and cause a very painful sting.