information on the biology of species and the ecology of habitats found around the coasts and seas of the British Isles

A bristleworm (Magelona filiformis)

Distribution data supplied by the Ocean Biogeographic Information System (OBIS). To interrogate UK data visit the NBN Atlas.



Magelona filiformis is a thin, thread-like segmented worm that reaches lengths of up to 8-10 cm and is either translucent, pink (mature females) or white (mature males). The body is divided into a head, 8-segmented thorax, abdomen of approximately 130 segments and a terminal pygidium. The head consists of a flattened, elongated, prostomium with small horns, a globular-shaped proboscis, a pair of palps and a long thin tentacle either side bearing two rows of papillae. The first segment adjacent to the head lacks chaetae or parapodia. Either side of the thoracic segments each bear foliose lobes dorsally, 15 dorsal chaetae and 10 ventral chaetae. The ninth chaetiger divides the thorax and abdomen, bears foliose lobes both dorsally and ventrally and is distinguished by the presence of 25-30 chaetae on both parapodia. Abdominal segments each bear widely-spaced foliose notopodial and neuropodial lobes with a short cirrus and row of horns and short rod-like dorsal and ventral lobes. Towards the posterior of the abdomen the neuropodia and notopodia are positioned increasingly to the posterior end of each segment. The most posterior end of the body is tapered into a pygidium bearing two anal cirri.

Recorded distribution in Britain and Ireland

Magelona filiformis is widespread on the coasts of Britain and Northern Ireland.

Global distribution



Magelona filiformis forms fragile tubles in clean to muddy sand on the lower shore.

Depth range


Identifying features

  • Long, thread-like body of approximately 140 segments.
  • Body grows up to 5-10 cm.
  • Long, slender tentacles either side of head bearing two rows of papillae.
  • Proboscis globular-shaped when everted.
  • Eyes absent.
  • Thoracic segments bear 15 dorsal chaetae and 10 ventral chaetae.
  • Distinctive ninth segment bears 25-30 chaetae both dorsally and ventrally.
  • Abdominal segments without chaetae bundles.
  • Foliose lobes present both dorsally and ventrally on ninth and abdominal segments but only dorsally on thoracic segments.

Additional information

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Further information sources

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  1. Costello, M.J., Bouchet, P., Boxshall, G., Emblow, C. & Vanden Berghe, E., 2004. European Register of Marine Species [On-line].,

  2. Fauchald, K., & Rouse, G. 1997. Polychaete systematics: past and present. Zoologica Scripta, 26(2), 71-138.

  3. Fiege, D., Licher, F. & Mackie, A.S.Y., 2000. A partial review of the European Magelonidae (Annelida : Polychaeta) Magelona mirabilis redefined and M. johnstoni sp. nov. distinguished. Journal of the Marine Biological Association of the United Kingdom, 80, 215-234.

  4. Foster-Smith, J. (ed.), 2000. The marine fauna and flora of the Cullercoats District. Marine species records for the North East Coast of England. Sunderland: Penshaw Press, for the Dove Marine Laboratory, University of Newcastle upon Tyne.

  5. Howson, C.M. & Picton, B.E., 1997. The species directory of the marine fauna and flora of the British Isles and surrounding seas. Belfast: Ulster Museum. [Ulster Museum publication, no. 276.]

  6. Picton, B.E. & Costello, M.J., 1998. BioMar biotope viewer: a guide to marine habitats, fauna and flora of Britain and Ireland. [CD-ROM] Environmental Sciences Unit, Trinity College, Dublin.

  7. Wilson, D.P., 1959. The polychaete Magelona filiformis sp.nov. and notes on other species of Magelona. Journal of the Marine Biological Association of the United Kingdom, 38(3), 547-556.


  1. National Biodiversity Network (NBN) Atlas website. Available from:

  2. OBIS,  2019. Global map of species distribution using gridded data. Available from: Ocean Biogeographic Information System. Accessed: 2019-01-17

  3. South East Wales Biodiversity Records Centre, 2018. SEWBReC Worms (South East Wales). Occurrence dataset: accessed via on 2018-10-02.


This review can be cited as:

Richards, S. 2007. Magelona filiformis A bristleworm. In Tyler-Walters H. and Hiscock K. (eds) Marine Life Information Network: Biology and Sensitivity Key Information Reviews, [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 17-01-2019]. Available from:

Last Updated: 12/09/2007