Akera bullata swimming

Dear Ian,
This is an interesting observation which has rarely been reported. The animal is Akera bullata, which is a very primitive Sea Hare rather than a nudibranch [see Akeroidea Fact Sheet]. They have a bubble-shaped external shell and although they spend most of their time crawling or burrowing in fine mud on sheltered shores and bays, they can at time form swimming swarms, often in quite large numbers. Some say swarming is involved with breeding, while others say it is the juveniles that usually swarm, but basically this 'swarming - swimming' behaviour has not been studied in detail and only reported in the scientific literature 3 or 4 times, so it is not possible to say anything very sensible about it.  The drawing alongside is from Morton & Holme (1955) who report spawning and swimming from April-July in the English Channel coast. Theanimals swim rather awkwardly with their heavy (shelled) end hanging down, more like large heavy flying beetles, than bees. I haven't any photos of living Akera bullata, but it is quite similar in shape to Akera soluta from the Pacific.

• Morton, J. E. and Holme, N. A. (1955) The occurrence at Plymouth of the marine opisthobranch Akera bullata, with notes on its habits and relationships. Journal of the Marine Biological Association, United Kingdom 34: 101-112

Best wishes,
Bill Rudman