''Chaetopterus'' or the parchment worm or parchment tube worm is a

genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial no ...

of marine

polychaete Polychaeta () is a paraphyletic class of generally marine annelid worms, commonly called bristle worms or polychaetes (). Each body segment has a pair of fleshy protrusions called parapodia that bear many bristles, called chaetae, which are ma ...

worm that lives in a tube it constructs in sediments or attaches to a rocky or

coral reef A coral reef is an underwater ecosystem characterized by reef-building corals. Reefs are formed of colonies of coral polyps held together by calcium carbonate. Most coral reefs are built from stony corals, whose polyps cluster in groups. ...

substrate. The common name arises from the

parchment Parchment is a writing material made from specially prepared untanned skins of animals—primarily sheep, calves, and goats. It has been used as a writing medium for over two millennia. Vellum is a finer quality parchment made from the skins of ...

-like appearance of the tubes that house these worms. Parchment tube worms are filter feeders and spend their adult lives in their tubes, unless the tube is damaged or destroyed. They are

plankton Plankton are the diverse collection of organisms found in water (or air) that are unable to propel themselves against a current (or wind). The individual organisms constituting plankton are called plankters. In the ocean, they provide a cruci ...

ic in their juvenile forms, as is typical for polychaete

annelid The annelids (Annelida , from Latin ', "little ring"), also known as the segmented worms, are a large phylum, with over 22,000 extant species including ragworms, earthworms, and leeches. The species exist in and have adapted to various ecolo ...

s. Species include the recently discovered deep water '' Chaetopterus pugaporcinus'' and the well-studied '' Chaetopterus variopedatus''.

Housing tubes

The tubes the worms live in are either attached to rocks, or, more commonly, buried in sandy bottoms in shallow waters. The worm has spines along its body segments that are modified for tunneling into the sandy substrate to create the u-shaped tube within which it lives. The tubes are upright u-shaped tunnels lined with mucous, then the parchment tube, with the worm living inside the parchment tube. Each parchment tube ends with a chimney of parchment that juts above the substrate. The tubes can be as long as 85 centimeters and up to 4 centimeters in diameter at the widest portion in the buried central part of the tube. The chimneys may be wider or much narrower than the rest of the tube.

Worm morphology

The worms are unique among the

worms in the highly derived

parapodia In invertebrates, the term parapodium ( Gr. ''para'', beyond or beside + ''podia'', feet; plural: parapodia) refers to lateral outgrowths or protrusions from the body. Parapodia are predominantly found in annelids, where they are paired, unjointe ...

of the mid-segments of its body that are used in its specialized filter feeding regime. The worm's parapodia are modified into the shape of fans and used to create suction and pump water through the worm's parchment living tube. The morphology of the structures are used in identifying species. The worm feeds by using modified structures on its midbody segments that create mucus nets to trap food passed through the net. A flow of water containing plankton and organic debris is created by "circular flaps" on three segments that create suction that draws water through the living tube.

Bioluminescence

Members of the genus have no organs for detecting light and live their entire adult lives in their buried tubes. In spite of this, known members of the genera exhibit strong

bioluminescence Bioluminescence is the production and emission of light by living organisms. It is a form of chemiluminescence. Bioluminescence occurs widely in marine vertebrates and invertebrates, as well as in some fungi, microorganisms including some ...

. When the worm is disturbed in its home it moves to the end of the tube away from the disturbance and near the disturbance it emits its feeding mucus with crystals that exhibit blue luminescence.

Commensal animals

Two species of filter-feeding crustaceans from different families may make their homes in the ''Chaetopterus'' tube, '' Polyonyx gibbesi'' (family Porcellanidae) and '' Pinnixa chaetopterana'' (family Pinnotheridae) ; while a third species, '' Tumidotheres maculatus'' is known to sometimes inhabit the tubes. ''Polyonyx'' and ''Pinnixa'' are almost always present in the tubes, generally as a pair of crabs, and both species may inhabit the tubes at the same time. However, breeding pairs of either species do not share the tubes with adults of the other species. The crustaceans may live most of their lives in the tubes, leaving in the case of disturbance by exiting through the chimneys at either ends or, when the chimneys are too narrow, by biting through the parchment tube. A nudibranch, '' Tenellia chaetopterana'' also lives within the tubes of a species of ''Chaetopterus''. It is hypothesised that this nudibranch feeds on the mucus net which ''Chaetopterus'' uses to trap its food or on the faeces of ''Chaetopterus''. '' Tenellia rolleri'' is another nudibranch with similar flattened morphology which lives in muddy areas with no obvious food source, but abundant ''Chaetopterus'' tubes. It is possible that it lives and feeds in a similar manner.Ekimova I., Deart Y. & Schepetov D. (2017)
Living with a giant parchment tube worm: a description of a new nudibranch species (Gastropoda: Heterobranchia) associated with the annelid ''Chaetopterus''.
Marine Biodiversity. DOI 10.1007/s12526-017-0795-z.

References

{{Taxonbar, from=Q5066721 Polychaete genera Canalipalpata Bioluminescent annelids Taxa named by Georges Cuvier