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

A sea slug (Polycera quadrilineata)

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



Polycera quadrilineata may grow up to 3.9 cm, but the maximum recorded length is 4.5 cm. Its body is translucent white with patches of yellow and orange pigments forming five longitudinal lines. Along the mid-line there is a row of oval blotches, merging towards the rear. Occasionally individuals have black streaks, blotches or fine spots on their backs. The front region of the head extends to form an oral veil. The edge of the foot is usually dotted with colour extended into a veil which is usually edged with yellow-orange colour with spots on the flank. The four frontal processes (frontal veil papillae) are coloured yellow. Two sensory organs (rhinophores) are present on its head, they have thick stalks which end with a yellow cylindrical knob. The eggs are spawned in a short white curved ribbon. This species is often found in large numbers.

Recorded distribution in Britain and Ireland

Common all around the British Isles.

Global distribution

Recorded from America to the Mediterranean.


Polycera quadrilineata occurs on encrusting sea mats (Bryozoa) from the intertidal and sublittoral zones to depths of about 60 m.

Depth range


Identifying features

  • Grows up to 3.9 cm.
  • Translucent white with patches of yellow and orange.
  • Five longitudinal lines of varying shades along the back.
  • Four processes on the oral veil.

Additional information

Polycera quadrilineata is sometimes confused with Polycera faeroensis. However Polycera faeroensis has 8 or more oral veil processes whereas Polycera quadrilineata has four, and the patches of yellow pigments on the body are absent from Polycera quadrilineata.

Listed by

- none -

Further information sources

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  1. Hayward, P.J. & Ryland, J.S. (ed.) 1995a. The marine fauna of the British Isles and north-west Europe. Volume 2. Molluscs to Chordates. Oxford Science Publications. Oxford: Clarendon Press.

  2. 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.]

  3. JNCC (Joint Nature Conservation Committee), 1999. Marine Environment Resource Mapping And Information Database (MERMAID): Marine Nature Conservation Review Survey Database. [on-line]

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

  5. Picton, B. E. & Morrow, C.C., 1994. A Field Guide to the Nudibranchs of the British Isles. London: Immel Publishing Ltd.

  6. Picton, B.E. & Morrow, C.C., 2000. Encyclopaedia of Marine Life of Britain and Ireland., 2003-09-18

  7. Picton, B.E., 2000. Nudibranchs of the British Isles., 2003-09-11

  8. Thompson, T. E. & Brown, G. H., 1976. British Opisthobranch Molluscs. London: Academic Press. [Synopses of the British Fauna, no. 8.]


This review can be cited as:

Edwards, R.V. 2008. Polycera quadrilineata A sea slug. 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 14-08-2018]. Available from:

Last Updated: 17/04/2008