Tube worm. View of a tube worm (phylum Annelida) with its tentacles extended, on the sea bed. The tube worm is a sessile (fixed) polychaete. The worms secrete a substance which hardens to form a snail-like calcified spiral tube (lower centre). These tubes protect the worms from predators. The worms feed on passing plankton by extending tentacles (yellow) covered in fine hairs into water currents. The tentacles waft the plankton towards the worms' mouth. Tube worms frequently attach themselves to rocks and animals as well as seaweed. Photographed in the Mediterranean Sea, Giglio, Italy.