Limacia clavigera (Müller, 1776)

09 November, 2003.
Stallion Rock, Loch Fyne on the west coast.
At 8 metres, a 22mm long animal on the tunicate Ascidia mentula. 
Water temperature 13 deg C. There always seems to be more of these lovely little animals around at this time of the year, or perhaps they are more noticeable as the kelp dies back.
Nikon 90SX with 105mm lens in Subal housing and housed SB26 flash.