A sea squirt (Ascidia conchilega)

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



Ascidia conchilega is a sessile, solitary sea squirt that grows to up to 6 cm in length and is greenish in colour. It has an elongate, oval-shaped body that is gelatinous in texture. The whole length of the left-hand side of the body is attached to the substrate. The body has a large dorsal tubercle with a horse-shoe shaped opening, and two inconspicuous siphons; a terminal inhalant oral siphon and a longer, exhalant atrial siphon that is positioned approximately two-thirds of the body length from the oral siphon. The oral siphon is surrounded by six to eight red , rounded lobes, whereas the atrial siphon is surrounded by six of the same. The inner surface of the oral siphon bears a ring of tentacles, and is linked to a large branchial cavity. The branchial cavity is perforated with rows of stigmata and bears small, irregular papillae on the right face of its dorsal lamina. The whole body is encased by a thin, translucent, cartilaginous test that has a smooth outer surface with small, rough projections and particles of shell attached.

Recorded distribution in Britain and Ireland

Ascidia conchilega is widespread on all coasts of Britain and Ireland.

Global distribution

Ascidia conchilega is widely distributed in north-west Europe, from the Faroes and west Norway to the mediterranean.


Ascidia conchilega is found from low water to depths of at least 1000 m. This species attaches to hard substrate, such as stones and shells, as well as the holdfasts of various algae. It also inhabits the underside of rocks in tidepools.

Depth range


Identifying features

  • Solitary sea squirt with elongate, oval-shaped body.
  • Body up to 6 cm in length.
  • Body attached to the substrate along entire length of left side.
  • Test is thin, translucent and smooth with small rough projections.
  • Greenish in colour with red spots on siphonic lobes.
  • Atrial siphon positioned two-thirds of body length from oral siphon.

Additional information

Ascidia conchilega is a filter-feeder. Individuals of this species are hermaphroditic and reproduce by externally fertilized eggs throughout January to December. Tadpole larvae, approximately 0.1 cm long, hatch from the eggs and settle on the substratum before metamorphosing into the adult form. This species is similar to Ascidia mentula which is larger, has a smooth surface and a grey to pink coloured, thick test.

Listed by

- none -


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  1. Centre for Environmental Data and Recording, 2018. IBIS Project Data. Occurrence dataset: https://www.nmni.com/CEDaR/CEDaR-Centre-for-Environmental-Data-and-Recording.aspx accessed via NBNAtlas.org on 2018-09-25.

  2. 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.

  3. Environmental Records Information Centre North East, 2018. ERIC NE Combined dataset to 2017. Occurrence dataset: http://www.ericnortheast.org.ukl accessed via NBNAtlas.org on 2018-09-38

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

  5. Kent Wildlife Trust, 2018. Kent Wildlife Trust Shoresearch Intertidal Survey 2004 onwards. Occurrence dataset: https://www.kentwildlifetrust.org.uk/ accessed via NBNAtlas.org on 2018-10-01.

  6. 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.

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

  8. OBIS (Ocean Biodiversity Information System),  2024. Global map of species distribution using gridded data. Available from: Ocean Biogeographic Information System. www.iobis.org. Accessed: 2024-07-25


This review can be cited as:

Richards, S. 2008. Ascidia conchilega 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 25-07-2024]. Available from: https://www.marlin.ac.uk/species/detail/38

Last Updated: 03/07/2008