Yellow-plumed sea slug (Berthella plumula)

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



Berthella plumula appears transparent and fragile with an oval, convex body, up to 6 cm in length. The shell is up to 3 cm long but internal, covered by the mantle which overlaps the shell edges. The mantle itself is smooth, and pale yellow to orange in colour, often having net-like markings down the middle. The edge of the mantle may actually be raised on the right side where an elongated gill is situated, for respiration. Its head has a noticeably flat oral veil with enrolled rhinophores (sensory processes). A conspicuous gland (the metapodal gland) develops at the posterior end of the body at a pre-sexual stage when the species is approximately 1.75-3 cm in length. When in danger acid glands in the skin secrete sulphuric acid for protection.

Recorded distribution in Britain and Ireland

This species is widely distributed around Britain and Ireland primarily west and south west England; north and southern Wales; Isle of Man; north, west and south west Ireland; north, west and eastern coasts of Scotland.

Global distribution



Berthella plumula is often found under stones, in clear rock pools on the lower shore and shallow water up to 10 m deep. Commonly found on Botryllus schlosseri.

Depth range


Identifying features

  • Smooth mantle, pale yellow to orange, often showing reticulate markings in the middle.
  • Body up to 6 cm long.
  • Internal shell up to 3 cm long, completely covered by mantle.
  • Sulphuric acid secreted by acid glands in skin for protection against predators.

Additional information

This is a slow moving opisthobranch and a specialised predator; feeding on compound ascidians. Breeding occurs in spring. Spiralled egg ribbons are attached to rocks, with the larva being planktonic.

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 accessed via on 2018-09-25.

  2. Conchological Society of Great Britain & Ireland, 2018. Mollusc (marine) data for Great Britain and Ireland - restricted access. Occurrence dataset: accessed via on 2018-09-25.

  3. Conchological Society of Great Britain & Ireland, 2018. Mollusc (marine) records for Great Britain and Ireland. Occurrence dataset: accessed via on 2018-09-25.

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

  5. Fenwick, 2018. Aphotomarine. Occurrence dataset Accessed via on 2018-10-01

  6. Kent Wildlife Trust, 2018. Kent Wildlife Trust Shoresearch Intertidal Survey 2004 onwards. Occurrence dataset: accessed via on 2018-10-01.

  7. National Trust, 2017. National Trust Species Records. Occurrence dataset: accessed via on 2018-10-01.

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

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

  10. Yorkshire Wildlife Trust, 2018. Yorkshire Wildlife Trust Shoresearch. Occurrence dataset: accessed via on 2018-10-02.


This review can be cited as:

Rowley, S.J. 2004. Berthella plumula Yellow-plumed sea slug. 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:

Last Updated: 27/08/2004