Dendrodoris denisoni or D. gunnamatta

June 22, 2000
From: P.Zylstra & H.Rothenfluh


Hi,

We saw quite a few of these nudis at Clifton Gardens Wharf in Sydney on 13 May 2000 in 3-7m water [New South Wales, Australia]. They were crawling on the silt, sponges and pylons. We found a pair mating on a pylon during the day -- they were still there when we came back at night and took a photo.
Are these Dendrodoris denisoni? We thought they might be the darker form D. gunnamatta that you described.

Cheers

Paula Zylstra
Harry Rothenfluh

hsrpz@netspeed.com.au

Zylstra,P. & Rothenfluh,H., 2000 (Jun 22) Dendrodoris denisoni or D. gunnamatta. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/2588

Dear Paula & Harry,

Thanks for the second photo today of an animal almost certainly feeding. It looks to me that in the top photo there is a very fresh 'bite' in the sponge. And in the lower photo they are definitely mating.

For those of you not familiar with the ways of nudibranchs, they are hermaphrodite which means they all have a full set of male and female reproductive organs. They reproductive openings are situated somewhere on the right side of the body, so if you see two animals with their right sides very close together, or attached, then you can be sure they are mating.

Now, is this Dendrodoris denisoni of Dendrodoris gunnamatta? It is certainly the animal that was named Dendrodoris gunnamatta, but as I discuss at the top of the page, I think that it is probably a colour form of the more brightly coloured Dendrodoris denisoni but it is a bit hard to prove either way. See Stephanie Clark's photo below. One good character we can often use to distinguish species of nudibranch from one another, is the shape of their radular teeth. Unfortunately species of Dendrodoris are suctorial feeders which have lost their teeth, so we can't use that character. One feature all the 'colour forms' of D. denisoni have in common are the bright blue spots on their mantle. You can clearly see them in the photo of the mating animals.

There don't seem to be any clear anatomical features to separate one colour form from another so it seems to me that one way we could help solve the problem of how many blue-spotted species there are is to get some information on what they eat, how big their eggs are, and the shape and colour of their egg ribbons. You have helped with a photo of one possible sponge food. What we need is some photos of their egg ribbons and more of them feeding. If we can find some differences in egg size and colour then it may be worth while looking more closely for anatomical differences. It may take a while to get this information but it's worth a go.

Best wishes,
Bill Rudman.

Rudman, W.B., 2000 (Jun 22). Comment on Dendrodoris denisoni or D. gunnamatta by P.Zylstra & H.Rothenfluh. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/2588

Factsheet

Dendrodoris denisoni

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