Archidoris pseudoargus

(Rapp, 1827)

This is the largest dorid nudibranch in the North Sea. It may reach 120 mm in length and the dorsal mantle, covered by blunt tubercles of various sizes, bears blotchy markings of yellow, brown, pink, green and white pigments. The variety flammea is reddish in colour all over. There are 8-10 tripinnate gills which are paler than the mantle; they often bear opaque white or sulphur-yellow pigment. The head bears vestigial blunt oral tentacles. The disruptive pigment pattern of this shallow water and sublittoral species renders it inconspicuous, especially when submerged (Archidoris pseudoargus); (A. pseudoargus-dorsal view).

It feeds upon encrusting siliceous sponges, chiefly Halichondria panacea and Hymeniacidon perleve.

A. pseudoargus has been recorded all around the British Isles, the Faeroes, Iceland, Norway (to Varanger Fjord), the Baltic Sea (to the Bay of Kiel), Atlantic France, Spain, Portugal, and numerous localities in the Mediterranean Sea (usually recorded under the name Archidoris tuberculata ), to 300 m (Distr. A. pseudoargus).