Biodiversity & Conservation

A sea slug - Onchidoris bilamellata

Onchidoris bilamellata

Image Jim Anderson - Onchidoris bilamellata. Image width ca 4 cm.
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Distribution map

Onchidoris bilamellata recorded (dark blue bullet) and expected (light blue bullet) distribution in Britain and Ireland (see below)

Why do the maps differ?

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Onchidoris bilamellata is not listed under any importance categories.

Taxonomy icon Taxonomy Taxon English term
Phylum Mollusca Snails, slugs, mussels, cockles, clams & squid
Class Gastropoda Snails, slugs & sea butterflies
Authority Linnaeus, 1767
Recent synonyms None
Map icon Recorded Distribution in Britain and Ireland Recorded all around Britain and Ireland.
Habitat information icon Habitat information Onchidoris bilamellata can be found in the intertidal and shallow sublittoral, to a depth of 20 m.
Text page icon Description Onchidoris bilamellata can grow to 4 cm in length and are usually white with a brown pattern on the mantle. However immature specimens and the occasional adult may be completely white in colour. It bears many (usually white) club shaped projections (tubercles) on its mantle and has two ringed sensory tentacles on its head. The numerous (up to 29) retractile gills are speckled brown around the edges and arranged in a horseshoe shape. The head extends to form an oral veil which lacks tentacles. The spawn is in the shape of a flattered coil attached to the substratum by one edge and contains many thousand eggs.
Identifying features
  • Grows up to 4 cm in length.
  • Dirty white colour with a brown pattern.
  • Horseshoe shaped gills.
  • Club shaped projections (usually white) on the mantle.
Additional information icon Additional information This species produces acid secretions from the mantle when disturbed. It is gregarious and feeds exclusively on barnacles, especially Semibalanus balanoides.

This review can be cited as follows:

Rose Edwards 2004. Onchidoris bilamellata. A sea slug. Marine Life Information Network: Biology and Sensitivity Key Information Sub-programme [on-line]. Plymouth: Marine Biological Association of the United Kingdom. [cited 19/05/2013]. Available from: <http://www.marlin.ac.uk/speciesinformation.php?speciesID=3958>