Onchidoris pusilla

(Alder & Hancock, 1845)

This is the darkest of the British onchidorids; it is inconspicuous and reaches a maximal length of only 9 mm. The dorsum is covered by dark brown spots most dense near the midline. The most reliable diagnostic feature is the presence all over the dorsal mantle of abundant small, spiculose, conical tubercles. (These are smaller and less elongated than the pallial tubercles of Onchidoris depressa or of O. oblonga .) Another characteristic feature is the white colour of both the rhinophores and the simple pinnate gills (up to nine in number).

The prey of this species consists of the bryozoans Escharella immersa , Microporella ciliata , Escharoides coccineus and Porella concinna .

There are sporadic reports from localities all around the British Isles and from the European Atlantic coast from Kristiansund in Norway to the Spanish Biscay coast, down to 80 m (Distr. O. pusilla).