Tritonia plebeia

Johnston, 1828

The body length reaches 30 mm (usually not more than 20 mm) and is pale yellow with brown mottling on the dorsum and flanks. Paler specimens prey upon the white octocoralline anthozoan Alcyonium ; darker ones are usually found on the yellow variety. Larger individuals are generally darker than juveniles. The gills number three pairs in a 4 mm specimen, four in a 9.5 mm specimen and six in a 16 mm specimen. Below 3 mm in body length gills are frequently lacking; such individuals may be difficult to identify. The oral veil is produced to form smooth, finger-like processes, two pairs in a 4 mm specimen, up to three (rarely four) pairs in adults 16 mm or more in length (T. plebeia-lateral view).

This tritoniid feeds upon Alcyonium digitatum , and is usually found around the bases of the colonies, in clear offshore waters.

It reaches its northern limit in Norway (Trondheims-fjord) and in the Faeroes (Distr. T. plebeia). Elsewhere it occurs on the Atlantic coasts of France, the British isles, Spain and Portugal and throughout the western Mediterranean Sea, perhaps extending as far as the Aegean Sea.