A sea squirt (Polyclinum aurantium)

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



Polyclinum aurantium is a round pear-shaped sea squirt colony. It is yellow to brown in colour usually coated in sand or detritus giving it a sandy noduled appearance. It is generally 1 cm to 1.5 cm high and 2 cm to 5 cm wide. Zooids make up irregular shaped lobes each with one or more exhalent (cloacal) openings. The zooid oral siphon is six lobed, the stomach wall smooth and the intestinal loop is twisted. Zooid morphology is distinctive to the species but requires microscopic identification.

Recorded distribution in Britain and Ireland

Polyclinum aurantium is recorded around all coasts of the British Isles.

Global distribution

Polyclinum aurantium is recorded in the North East Atlantic from Norway to the Mediterranean.


Polyclinum aurantium is commonly found in the upper infralittoral zone and in wave exposed gullies. It can be found attached to rock faces, algae and stones.

Depth range

0-100 m

Identifying features

  • Round pear-shaped colony, roughly 1-1.5 cm in height and 2-5 cm in width.
  • Yellow to brown in colour usually coated in sand.
  • Zooids form irregular shaped lobes with one or more exhalent (cloacal) openings.
  • Zooid oral siphon is six lobed.
  • Zooid stomach wall is smooth and the intestinal loop is twisted.

Additional information

Polyclinum aurantium larvae are produced from May to October. The colony enters an overwintering phase where it then divides and reproduces asexually before feeding in the spring (Picton & Morrow, 2016). Polyclinum aurantium are also known to host copepods Haplostomides scotti and Haplostomides hiber (Gotto, 1952; Ooishi, 1994; Ooishi, 2002).

Listed by

- none -


  1. De Kluijver, M.J. & Ingalsuo, S.S., 2021. Polyclinum aurantium. Macrobenthos of the North Sea - Tunicata Marine Species Identification Portal ETI Bioinformatics. (22/04/2021). http://species-identification.org/species.php?species_group=tunicata&id=39

  2. Hayward, P.J. & Ryland, J.S. (ed.) 2017. Handbook of the marine fauna of North-West Europe. Oxford: Oxford University Press.

  3. Nakauchi, M., 1981. Development and budding in the oozooids of Polyclinum aurantium (a colonial ascidian) (Protochordata)*. Journal of Zoology, 194 (1), 1-9. DOI https://doi.org/10.1111/j.1469-7998.1981.tb04574.x

  4. Ooishi, S., 2004. Haplostomides hawaiiensis, new species (Copepods: Cyclopoida: Ascidicolidae), associated with the ascidian Polyclinum constellatum at Honolulu, Hawaii. Hydrobiologia, 292, 89-96. DOI https://doi.org/10.1007/BF00229927

  5. Ooishi, S., 2005. Haplostomides hibernicus (Copepoda: Cyclopoida) Living in the Compound Ascidian Polyclinum Aurantium. Journal of Crustacean Biology, 25(2), 181-189. DOI https://doi.org/10.1651/c-2537

  6. Picton, B.E. & Morrow, C.C.,2016b. Polyclinum aurantium Milne-Edwards, 1841. [In] Encyclopedia of Marine Life of Britain and Ireland.Available from http://www.habitas.org.uk/marinelife/species.asp?item=ZD340 Accessed on 2021-04-22


  1. NBN (National Biodiversity Network) Atlas. Available from: https://www.nbnatlas.org.

  2. OBIS (Ocean Biodiversity Information System),  2024. Global map of species distribution using gridded data. Available from: Ocean Biogeographic Information System. www.iobis.org. Accessed: 2024-06-12


This review can be cited as:

Nash, R.A., 2021. Polyclinum aurantium A sea squirt. 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 12-06-2024]. Available from: https://www.marlin.ac.uk/species/detail/2337

Last Updated: 27/04/2021