Phoronida
They occur at depths up to 400 metres, but mainly between 0 to 70 metres. The life span is thought to be about a year. The adults are tube worms, and secrete chitinous tubes in which they live. These tubes can be buried in the mud or sand or rest on the surface of a rocky substrate. If on rocks, they may live in colonies with their tubes become twisted around each other for support. Some species can dissolve away holes in rocks such as limestone, calcareous seashells or even cement piers; they then live in these holes which they line with their secreted tubes.