Any of various small, mostly solitary, wormlike marine invertebrates of the phylum Phoronida. As adults, phoronids live in the ocean floor in a tube that they secrete made of chitin. They have a U-shaped digestive tract and feed by filtering food particles with a ciliated structure called a lophophore. The larvae of phoronids are very different in appearance and are free-swimming. Phoronids are thought to be related to the brachiopods and bryozoans.