Acorn worms are solitary worm-shaped organisms. They generally live in burrows (the earliest secreted tubes)[2] and are deposit feeders, but some species are pharyngeal filter feeders, while the family Torquaratoridae are free living detritivores. Many are well known for their production and accumulation of various halogenated phenols and pyrroles.[3] Pterobranchs are filter-feeders, mostly colonial, living in a collagenous tubular structure called a coenecium.[4]