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

A sea squirt (Ascidia mentula)

Distribution data supplied by the Ocean Biogeographic Information System (OBIS). To interrogate UK data visit the NBN Atlas.
Only coastal and marine records shown



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

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Further information sources

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  1. Bruce, J.R., Colman, J.S. & Jones, N.S., 1963. Marine fauna of the Isle of Man. Liverpool: Liverpool University Press.

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

  3. Crothers, J.H. (ed.), 1966. Dale Fort Marine Fauna. London: Field Studies Council.

  4. Dipper, R., & Powell. A., 1984. Field guide to the water life of Britain. London: Reader's Digest Association Limited.

  5. Fish, J.D. & Fish, S., 1996. A student's guide to the seashore. Cambridge: Cambridge University Press.

  6. Hayward, P., Nelson-Smith, T. & Shields, C. 1996. Collins pocket guide. Sea shore of Britain and northern Europe. London: HarperCollins.

  7. Hayward, P.J. & Ryland, J.S. (ed.) 1995b. Handbook of the marine fauna of North-West Europe. Oxford: Oxford University Press.

  8. 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.]

  9. MarLIN (Marine Life Information Network), 2005. SEArchable BEnthic Data (SEABED) Map [on-line]. Data Access Sub-programme, Marine Life Information Network for Britian and Ireland,

  10. MBA (Marine Biological Association), 1957. Plymouth Marine Fauna. Plymouth: Marine Biological Association of the United Kingdom.

  11. Millar, R.H., 1970. British Ascidians London: Academic Press.[Synopses of the British Fauna, no. 1.]

  12. Moen, F.E. & Svensen, E., 2004. Marine Fish & Invertebrates of Northern Europe. Southend-on-Sea: Aqua Press.

  13. National Biodiversity Network (NBN) Atlas website. Available from:  Accessed 01 April 2017

  14. Naylor, P., 2003. Great British Marine Animals. Plymouth: Sound Diving Publications.

  15. 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.


This review can be cited as:

Rowley, S.J. 2008. Ascidia mentula A sea squirt. 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 20-08-2018]. Available from:

Last Updated: 03/07/2008