A snail in the gastropod family Vermetidae. Worm shells are gregarious species forming an intertwining mass of long, white, worm-like tubes, often sunken into a reef substrate. They get their common name of "worm shell" because their shells superficially resemble the shells of some tube-building marine polychaete worms. After a short motile existance, they cement their shell to a hard substrate, and as they grow, the shells may coil or meander over the substrate producing a tube that looks quite like a tube worm. Worm shells are filter-feeders which spin a mucus net to trap floating food particles, such as plankton.