Cratena peregrina mating or fighting ?

August 24, 2006
From: Dominique Horst


Hello Bill,

We still have many Cratena peregrina laying at this time. And last dive we observed a strange behaviour between two. I've make a choice between many photos I could take during this long scene. I've tried to take short clip, but I failed. During 6 or 7 minutes we observed two C. peregrina (small size) quit jumping on together, like a fighting. When I had a look to the photo taken, I saw a kind of green-brown powder around one of them. Could this was a scene of matting more than fighting ?

Locality: Cap d'Antibes, 15m, France, Mediterranean sea, 08 August 2006, vertical rock. Length: 10mm. Photographer: Dominique Horst.

I was very surprised of their animation, as usually slug are not moving very fast...?

Thanks in advance for your help and opinion.
Kind regards,
Dominique

dominique.horst@wanadoo.fr

Horst, D., 2006 (Aug 24) Cratena peregrina mating or fighting ?. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/17516

Dear Dominique,
Glaucid aeolids are well known for being a bit aggressive so I guess you are right - they are doing a bit of mating and fighting. I suspect the 'green-brown powder' you mentioned is faecal matter. Nudibranchs will often empty their intestines when disturbed - and the anus is quite close to the reproductive openings.  In the photo alongside, I have ringed what looks like brownish faecal matter, and two white sausage-shaped structures. I wouldn't be surprised if they are the egg masses of a parasitic copepod living on the back of the lower aeolid [as in your earlier message #17130 ].

Best wishes,
Bill Rudman

Rudman, W.B., 2006 (Aug 24). Comment on Cratena peregrina mating or fighting ? by Dominique Horst. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/17516

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