Phoronids secrete characteristic rigid tubes consisting of layers of chitin to which adhere particles of sediment and debris from the animal's immediate environment. Phoronids occur singly, vertically embedded in soft sediment (sand, mud, or fine gravel) or form tangled masses of many individuals buried in, or encrusting, rocks and shells. Phoronis australis is associated with cerianthid anemones in the tube in which it buries. In some habitats phoronids are very abundant, reaching several tens of thousand of individuals per 11 ft2 (1 m2).

Predators of phoronids are not well known, but they include fishes, gastropods, and nematodes.

The larval actinotroch is a familiar component of plankton.

A phoronid worm (Phoronopsis californica). (Photo by Lawrence Naylor/ Photo Researchers, Inc. Reproduced by permission.)

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