Re: Mating behaviour

March 3, 2003
From: Hans Tibboel

Dear Bill,
Thanks for your comments. The mating nudibranchs were the Risbecia tryoni and Chromodoris annulata and they were located on a wall at Black Rock in Myanmar at approx. 6 meter depth. Our on board photo-pro Mark Strickland took slide pictures of the mating and may be able to post those later on. We're both fulltime working on the boat and do not have much time to check our mail but I will try to keep you updated. Mark discovered in Myanmar a few years ago a new Halgerda that has been named after him (Halgerda stricklandi) and we still regularly come across nudibranchs that we have never seen before. Personally I do not carry any underwater camera gear but have also a great passion for seaslugs and nudibranchs.
Hans Tibboel

Dear Hans,
I would very much like to see some photos as I would like to check the identity of the two animals and just see whether they were actually mating. If you have a look at two earlier messages, one from Stuart Hutchison and the other from Mike Miller, you will that they both report R. tryoni and the yellow-spotted Risbecia pulchella in close contact with each other. R. pulchella is quite similar to C. annulata in colour, and close proximity can suggest mating. Species of Risbecia have this peculiar, and very characteristic, trailing behaviour where one animal follows another - often with the head in actual contact with the tip of the leading animals foot. They seem to be attracted to each other's mucus trail and the photos I mention suggest that sometimes they get confused with the mucus of their close relatives.

Whatever Mark has photographed it is very interesting. It will either confirm that these two species of Risbecia are liable to get confused, or it will show two 'species' mating. In either case it will be worth further investigation.
Bill Rudman

Rudman, W.B., 2003 (Mar 3). Comment on Re: Mating behaviour by Hans Tibboel. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

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