Cuthona yamasui aggregation
August 19, 2009
From: Brian Mayes
Concerning message #11017:
Dear Bill,
I'm interested to hear what you think about this aggregation of Cuthona yamasui or Trinchesia yamasui as another well known forum seems to call them now. Normally aggregations like this seem to collect around a food source, but as far as I know C. yamasui eats only hydroids and it doesn't look like they are grouped around hydroids in the photo. At the top of the photo there is a an egg ring so perhaps this is some sort of mass mating or egg laying. By the way, if you happen to work out how many are in the photo, please let me know. :-)
Locality: Secret Bay, Mainit, Anilao, 14 metres, Batangas, Philippines, Philippines Sea, 5 February 2009, Sandy sloping bay. Length: 45 mm. Photographer: Brian Mayes.
Kind Regards
Brian Mayes
brian.r.mayes@gmail.com
Mayes, B.R., 2009 (Aug 19) Cuthona yamasui aggregation. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/22548Dear Brian,
I could be wrong but I suspect the egg ribbon was produced by some dorid nudibranch rather than an aeolid. There are a few aeolid species, like Phestilla melanobrachia, with similarly shaped egg ribbons, but it is unusual. If the eggs do belong to the Cuthona I still can't say whether they aggregated for mating or whether they mated because they had aggregated for some other reason. Some large aeolids, especially the coral eaters, tend to aggregate in crevices during the day, or under the coral colony [hiding from predators] and emerge at night to feed. Perhaps your animals were doing there best to hide during the day. The hydroids this species apparently eats have quite fearsome stings, so perhaps they are quite well protected when they are on a big healthy hydroid colony. Perhaps they have eaten out such are hydroid colony and have lost their protection? - don't quote me on that - just throwing around a few ideas.
Best wishes,
Bill Rudman
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