In December I posted a series of shots entitled "Carnivorous Nudibranch", depicting what I thought was a nudibranch eating some kind of gastropod. Leslie Harris, Collection Manager of Allan Hancock Foundation Polychaete Collection at the Natural History Museum of Los Angeles County, saw the posting and suggested that I write to Dr. Bill Rudman, Principal Research Scientist in the malacology department at the Australian Museum, Sydney.
Here's a letter I submitted yesterday to Dr. Rudman at the Sea Slug Forum.
Aglajid eating a benthic ctenophore
January 13, 2006
From: Brian Francisco
Leslie Harris suggested that I send you the attached photographs. They depict an opistobranch (Leslie believes either in the family Aglajidae or Gastropteridae) eating a benthic ctenophore, genus Coeloplana. The photographs were taken on a sandy slope at 12M about 25 km west of the capital in East Timor.
Although the ctenophore was nearly the same size as the opistobranch (3-4 cm), the latter had no trouble engulfing the former. The event happened rather quickly, with no hesitation whatsoever, perhaps 8-10 seconds. In the third photo, a branched feeding tentacle can be seen coming off the right side of the ctenophore, even while most of it's body is inside the opistobranch.
The opistobranch then quickly buried itself.
Francisco, B., 2006 (Jan 13) Aglajid eating a benthic ctenophore. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find.cfm?id=15543
This is Dr. Rudman's response.
I am glad Leslie encouraged you to send this message. This is a whole series of 'firsts'. I suspect it is the first record of a benthic ctenophore being eaten by an opisthobranch, and the opisthobranch is almost certainly an aglajid, but I am pretty sure it's an unknown species. From the general shape, it is possibly a species of Philinopsis but the slender pointed tip to the posterior edge of the head shield is rather unusual. It reminds me a lot of the animal I have on the Forum as Aglajid sp 9. I wonder if the similarity in colour between the aglajid and the ctenophore is mere coincidence?
We don't know much about the biology of benthic ctenophores, in fact when I do a web search I usually end up on the Sea Slug Forum, where we have photos of a number of species, and some spectacular shots of animals with their feeding tentacles greatly expanded. Aglajids are unusual opisthobranchs because most have lost their radular teeth and so have evolved ways of feeding which involve either sucking in their prey whole - like eating a piece of spaghetti - in the case of the worm-eating Melanochlamys, or engulfing it by everting a large cylindrical buccal bulb - in the case of Philinopsis - which feeds on cephalaspidean bubble shells. Your animal has a foregut then, which is quite capable of engulfing a large prey item such as a benthic ctenophore.
To my knowledge no aglajid has been reported to feed on such prey before. You have made a very interesting discovery.
Rudman, W.B., 2006 (Jan 13). Comment on Aglajid eating a benthic ctenophore by Brian Francisco. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find.cfm?id=15543