page_title: Phoronid
section_title: Ecology
hierarchical_section_title: Phoronid / Ecology
caption_attribution_description: English: Phoronis hippocrepis photographed in shallow water in Italy. Photo by Maria Grazia Montanucci.
context_page_description: Phoronids are a small phylum of marine animals that filter-feed with a lophophore, and build upright tubes of chitin to support and protect their soft bodies. They live in most of the oceans and seas, including the Arctic Ocean but excluding the Antarctic Ocean, and between the intertidal zone and about 400 meters down. Most adult phoronids are 2 cm long and about 1.5 mm wide, although the largest are 50 cm long.
  The name of the group comes from its type genus: Phoronis.
context_section_description: Phoronids live in all the oceans and seas including the Arctic  and excepting the Antarctic Ocean, and appear between the intertidal zone and about 400 meters down. Some occur separately, in vertical tubes embedded in soft sediment such as sand, mud, or fine gravel. Others form tangled masses of many individuals buried in or encrusting rocks and shells. In some habitats populations of phoronids reach tens of thousand of individuals per square meter. The actinotroch larvae are familiar among plankton, and sometimes account for a significant proportion of the zooplankton biomass.
  Phoronis australis bores into the wall of the tube of a cerianthid anemone, Ceriantheomorphe brasiliensis, and uses this as a foundation for building its own tube. One cerianthid can house up to 100 phoronids. In this unequal relationship, the anemone experiences no significant benefits nor harm, while the phoronid benefits from: a foundation for its tube; food (both animals are filter-feeders); and protection, as the cerianthid  withdraws into its tube when danger threatens, and this alerts the phoronid to retract into its own tube.
  Although predators of phoronids are not well known, they include fish, gastropods (snails), and nematodes (tiny roundworms). Phoronopsis viridis, which reaches densities of 26,500 per square meter on tidal flats in California (USA), is unpalatable to many epibenthic predators, including fish and crabs. The unpalatability is strongest in the top section, including the lophophore, which is exposed to predators when phoronids feed. When the lophophores were removed in an experiment, the phoronids were more palatable, but this effect reduced over 12 days as the lophophores regenerated. These broadly effective defenses, which appear unusual among invertebrates inhabiting soft sediment, may be important in allowing Phoronopsis viridis to reach high densities. Some parasites infest phoronids: progenetic metacercariae and cysts of trematodes in phoronids' coelomic cavities; unidentified gregarines in phoronids' digestive tract; and an ancistrocomid ciliate parasite, Heterocineta, in the tentacles.
  It is unknown whether phoronids have any significance for humans. The International Union for Conservation of Nature (IUCN) has not listed any phoronid species as endangered.
caption: A dense colony of phoronids[1]
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