Cross-species matings - Chelidonura

April 10, 2003
From: Richard Willan

Dear Bill,
Since opisthobranchs are inherently rare in time and space, it follows that, theoretically, there should be more cross-species matings when individuals encounter each other than in relatively commoner molluscs. I have not seen any instances of cross-species matings in opisthobranchs myself, but believe I have documented the result of one such mating, that is a naturally-occurring hybrid individual. In the paper I published with Riccardo Cattaneo-Vietti in 1995 (on page 13), I described and illustrated one specimen of Chelidonura from Palau that seemed to be a hybrid of C. amoena with C. electra because it possesed pigmentation and shape characteristic of both species. Could you widen this page to include possible hybrids between known opisthobranch species like this one as well as records of both cross-species matings?

• Willan, R.C. & R. Cattaneo-Vietti (1995) New data on Chelidonura amoena Bergh, 1905 (Opisthobranchia: Cephalaspidea: Aglajidae). The Beagle, Records of the Museums and Art Galleries of the Northern Territory, 12: 9-18.

Regards,
Richard

richard.willan@nt.gov.au

Thanks Richard,
I'm happy to add hybrids to the page, although it is one step removed from actually seeing interactions between two species. Unless we actually see the mating and isolate the resulting eggs, saying that a particular animal is the result of a cross-species mating is a pretty risky business. It also raises the question of species definition. If two 'species' are unable to distinguish between each other, is this a comment on our ability to determine what is a species?

In the particular case of these two 'species' of Chelidonura, C. electra was named by me so I might be thought to have an interest in its future - Who would want such a spectacular animal to be lumped with dull, and much older C. amoena? Despite that, if I consistently found animals which were intermediate in colour I would be inclined to consider them to be colour variants of one species rather than hybrids of two. It is certainly something worth looking into. If anyone has further photos of these two species to add to the ones we already have, they would be very welcome.
Best wishes,
Bill Rudman

Rudman, W.B., 2003 (Apr 10). Comment on Cross-species matings - Chelidonura by Richard Willan. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/9637

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