Polycera quadrilineata
(Muller, 1776)

Order: NUDIBRANCHIA
Suborder: DORIDINA
Family: Polyceridae
Subfamily: Polycerinae

DISTRIBUTION

Western Europe from Iceland and Greenland south to the Mediterranean (Italy, France, Spain, Turkey).

PHOTO

UPPER: Feeding on Membranipora membranacea on Laminaria digitata in Laminarian algae belt. United Kingdom, Wales, Swansea, Oxwich wreck, 24 June 1993, 1.2 metres. PHOTOS: Daniel G. Geiger. See message for further photos of colour variation and egg masses

This common European polycerid grows to about 40 mm in length. It is white with blotches of yellow or orange. Sometimes black spots or speckling can be present. The orange marks usually from a line down the dorsal midline, with others in the sides and dorsal part of the posterior foot. In some animals, as illustrated here, black or dark blue speckling occurs. The rhinophores, gills and tentacles are tipped with orange, and in some cases the gills are edged in orange. There usually four pointed papillae around the anterior (head end) of the mantle. It feeds on ectoproct bryozoans, especially Membranipora membranacea, but is also reported from a number of other species.

There is a dark blue form of Polycera quadrilineata which closely resembles the blue adult form of Polycera aurantiomarginata. P. aurantiomarginata always has an orange border to the foot as its name suggests. The two species can also be distinguished in the colour of the rhinophore club - in P. aurantiomarginata at least the upper half, but not the tip is bluish-black, and in P. quadrilineata, yellow or orange. Similarly the apical part of the gills are black in P. aurantiomarginata and yellow in P. quadrilineata. Another difference is in the number of cephalic processes on the anterior mantle edge - - in P. aurantiomarginata there are 6-7 and in P. quadrilineata usually 4.

Reference:
• Thompson, T.E. & Brown, G.H. (1984) Biology of Opisthobranch Molluscs, Vol 2. Ray Society: London.

Authorship details
Rudman, W.B., 1999 (August 5) Polycera quadrilineata (Muller, 1776). [In] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/factsheet/polyquad

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