A sea squirt (Ascidia mentula)

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



Ascidia mentula is a large solitary sea squirt that can be over 18 cm in length. Its elongate body is usually smooth, often with low rounded swellings. The test is thick, cartilaginous and translucent red - pink, or greenish - olive green, although it can be grey in low light deeper waters. This species is usually attached to the substratum on its left side, unlike most ascidians which attach at the base. Its siphons are inconspicuous with small lobes often bearing white bands or spots. The inhalant (oral) siphon is terminal and the exhalant (atrial) siphon is half to three quarters down the body and can be obscured by detritus and encrusting growths.

Recorded distribution in Britain and Ireland

Ascidia mentula has been commonly recorded on the coasts of Britain and Ireland but with few records on the east coasts of England and Scotland.

Global distribution



This species can be found on the lower shore down to 2300 meters depth. Often found in shaded gullies and crevices on the rocky shore and attached to Laminaria holdfasts but also on large shells and stones on sand and mud. This species is tolerant of salinities down to 20.

Depth range


Identifying features

  • Large elongate body over 18 cm long.
  • Thick, cartilaginous, translucent test.
  • Usually red-pink or greenish-olive green but can be grey in deeper waters.
  • Attached to the substratum on its left side.
  • Small siphons; exhalant terminal, inhalant half to three quarters down the body.

Additional information

Ascidia mentula is fertilized externally and produces a tadpole larvae up to 0.8 mm in length, with a short planktonic phase. Breeding in this species occurs throughout the year but predominantly during the summer. The branchial sac of Ascidia mentula is commonly inhabited by the pea crab Pinnotheres pinnotheres or the copepod Notopterophorus papilio. The small bivalve Modiolarca tumida can also live commensally in the test. Ascidia mentula may be mistaken for Ascidia virginea which has a smooth, retangular, transparent rose-pink test with red veins on the mantle.

Listed by

- none -


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  1. Centre for Environmental Data and Recording, 2018. Ulster Museum Marine Surveys of Northern Ireland Coastal Waters. Occurrence dataset https://www.nmni.com/CEDaR/CEDaR-Centre-for-Environmental-Data-and-Recording.aspx accessed via NBNAtlas.org on 2018-09-25.

  2. Fenwick, 2018. Aphotomarine. Occurrence dataset http://www.aphotomarine.com/index.html Accessed via NBNAtlas.org on 2018-10-01

  3. Manx Biological Recording Partnership, 2018. Isle of Man historical wildlife records 1990 to 1994. Occurrence dataset:https://doi.org/10.15468/aru16v accessed via GBIF.org on 2018-10-01.

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

  5. OBIS (Ocean Biodiversity Information System),  2024. Global map of species distribution using gridded data. Available from: Ocean Biogeographic Information System. www.iobis.org. Accessed: 2024-05-23

  6. South East Wales Biodiversity Records Centre, 2018. SEWBReC Marine and other Aquatic Invertebrates (South East Wales). Occurrence dataset:https://doi.org/10.15468/zxy1n6 accessed via GBIF.org on 2018-10-02.


This review can be cited as:

Rowley, S.J. 2008. Ascidia mentula 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 23-05-2024]. Available from: https://marlin.ac.uk/species/detail/8

Last Updated: 03/07/2008