Terebellids build thin, membranous, sand-encrusted tubes in soft mud and sand. They extend their feeding tentacles from the entrance of the tube like spaghetti over the surface of the nearby sediment. The tentacles are extended out from the burrow by ciliary creeping and they can be retraced by muscular action. Mucus and ciliary action on the feeding tentacles transports small organic particles from the sediment to the mouth, especially along a groove along one side. Mucus and ciliary action on the feeding tentacles transports small organic particles from the sediment to the mouth. The tube of Thelepus crispus
is usually made of fragments of shell, stone, and other detritus, is nearly 1 cm wide, and is cemented to the undersurface of or between rocks. It may leave its tube when disturbed and later build a new one. They circulate water through their burrows. The major phosphagen in these worms is phosphoarginine; phosphotaurocyamine is also present. Commensals include the polychaete scaleworms Halosydna brevisetosa
and Hololepidella tuta
There are several genera of terebellids that are difficult to tell apart in the field. The feeding tentacles of Thelepus has threadlike, unbranched tentacles, and gills of similar length. Neoamphitrite and Terebella have dark, branching tentacles, which are longer than the gills which are white. Neoamphitrite has 17 thoracic segments while Terebella has 23 to 28.
Members of Family Terebellidae have special pumping vessels at the base of the gills to actively pump blood through them.