Common elongated horseshoe worm (Phoronis muelleri)

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



The horseshoe worm Phoronis muelleri is elongated and worm- shaped. The mouth is surrounded by a characteristic horseshoe shaped arangement of tentacles known as the lophophore. Phoronis muelleri can be up to 12 cm in length but less than 1 mm in width. The body is a pinkish colour and the lophophore is transparent, sometimes with spots. The lophophore of Phoronis muelleri sometimes has medially turned ends and the numerous tentacles are notably shorter near the mouth but may reach up to 2 mm in length.

Recorded distribution in Britain and Ireland

Found all around British coasts and has been recorded off the north-east coast of Ireland.

Global distribution



Phoronis muelleri penetrates vertically into muddy to sandy substrates, often with a high organic content and with an abundance of detritus and suspended material. It can be found from the intertidal zone to a depth of up to 400 m. It is frequently recorded in Macoma and Amphiura communities. Phoronis muelleri occurs in either boring or encrusting forms and may secrete and live in a membranous, cylindrical tube.

Depth range


Identifying features

  • Up to 12 cm in length, 1 mm in width.
  • Horseshoe shaped lophophore with short tentacles less than 2 mm in length.
  • Tentacles shorten towards the mouth.
  • No inward fold at the base of the lophophore.
  • The nephridia (kidney-like organ) has only one funnel.
  • Only one giant nerve fiber is present.

Additional information

Phoronida have a characteristic ciliated and free-swimming pelagic larva, known as Actinotrocha. Separate names for larval and adult forms may still be used in taxonomy (Emig, 1979).

Listed by

- none -


  1. Emig C.C., Çinar M.E. & Ergen, Z., 2003. Phoronida from the Eastern Mediterranean and Black Sea. Cahiers de Biologie Marine, 44, 185-190.

  2. Emig, C.C., 1979. British and other phoronids. London, Academic Press

  3. 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.]


  1. Centre for Environmental Data and Recording, 2018. Ulster Museum Marine Surveys of Northern Ireland Coastal Waters. Occurrence dataset accessed via on 2018-09-25.

  2. Environmental Records Information Centre North East, 2018. ERIC NE Combined dataset to 2017. Occurrence dataset: accessed via on 2018-09-38

  3. NBN (National Biodiversity Network) Atlas. Available from:

  4. OBIS (Ocean Biodiversity Information System),  2024. Global map of species distribution using gridded data. Available from: Ocean Biogeographic Information System. Accessed: 2024-06-22


This review can be cited as:

Barnes, M.K.S. 2008. Phoronis muelleri Common elongated horseshoe worm. In Tyler-Walters H. and Hiscock K. Marine Life Information Network: Biology and Sensitivity Key Information Reviews, [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 22-06-2024]. Available from:

Last Updated: 03/04/2008