All marine and live in chitinous tubes implanted in muddy or sandy sediments or attached to solid surfaces; sessile, but can move within theit tubes. Have giant nerve fibre that allows the animal to withdraw rapidly. Found from intertidal to 400 m. ~12cm long, and in form of elongated cllindircal sac. No appendages but the lophophore.
Lophophorate - trimeric construction: Protocoel, mesocoel and metacoel. Anterior body - mesocoel, bears lophophore and contains main nervous system. Trunk - metacoel, not specialized except for a bulb in the end (contains stomach and holds the aniaml in tube). Protocoel only in early stages, than reduced to epistome - a flap of tissue covering the mouth.
Body support by hydroskeleton, musculature weak, only limited movement if removed from tube.
Extensive circulatory system between lophophore and stomach - probably for nutrient and oxygen transport; have afferent and efferent branches and haemal plexus. No heart. Blood contains red blood particles with haemoglobin as respiratory pigment.
Excretion by pair of metanephridia in the trunk, each with 2 nephrostomes.
Asexual reproduction by budding or by transverse fission obseved in 2 species.
Separate sexes, some species hermaphroditic. Gametes excreted outside via nephridia, fertilization external.
All but 1 species have an unique actinotroph larva.