North Atlantic - from nthn France & British Isles to Iceland, Greenland, Arctic Russia and south to Connecticut. North Pacific - Alaska, British Columbia, Washington.
On bryozoan colony [Membranpora?] growing on kelp. Southern Maine, Atlantic coast, USA. Approx 5mm long. Photos: Charlotte Richardson.
Widespread common small species on both sides of the North Atlantic where it is difficult to distinguish externally from Adalaria proxima. It grows to about 14mm and varies in colour from white to cream-yellow. The mantle bears rounded (sometimes stalked) spiculate tubercles which are more slender towards the edge of the mantle. The tubercles are usually flat-topped and the long spicules may project from the surface (see lower left photo). It feeds on a wide variety of encrusting bryozoans but its main diet seems to be Electra pilosa and Mebranipora membranacea.
From the many studies on this animal we know it is a cold adapted species which spawns in spring, and early summer in more northern regions. It has an annual lifecycle and has the water temperature rises, it ceases feeding, and the gut and digestive gland tissue is converted into a final batch of gamtes before starving to death. The eggs are planktotrophic and can spend up to 60 days in the plankton before settlement. They grow to adult size over winter.
• Bleakney, J.S., (1996) Sea Slugs of Atlantic Canada and the Gulf of Maine
• Thompson, T.E. & Brown, G.H. (1984) Biology of Opisthobranch Molluscs, Vol 2. Ray Society: London.
• See List of taxonomic & ecological publications on Onchidoris muricata & Adalaria proxima.
Rudman, W.B., 2001 (July 3) Onchidoris muricata Muller, 1776. [In] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/factsheet/onchmuri
Adalaria or Onchidoris from California
From: Clinton Bauder, August 8, 2007
Onchidoris muricata from New England
From: Paul Young, July 5, 2001