Spirorbis spirorbis is a species of coiled polychaete worm that is classified within the Annelida phylum. It can be found in Ireland and Britain from the English Channel to northern areas of Norway. It attaches itself to eelgrass and seaweed in shallow water in small groups. The shell of this species is white in color and has a peripheral flange that attaches to the floating seaweeds. The worm lives inside of this shell and reaches an average length of about.1 inches. It is typically orange in color and has a short body with ten tentacles on the end, which are used to filter food out of the surrounding water. One tentacle, which is slightly larger and shaped like a saucer, is used as an operculum that can protect the worm from desiccation and predators.
Like other species of worm, Spirorbis spirorbis is hermaphroditic. It reproduces within the shell, releasing its larvae after they have developed to an advanced stage of free-living larvae. These larvae swim around for a few hours until they find a suitable piece of seaweed, which is often times the same seaweed that their parent lives on.
Image Caption: Spirorbis spirorbis, on kelp, Mull, Scotland. Credit: Paul Adams/Wikipedia