Roboastra gracilis from Mozambique

March 3, 2005
From: Riaan Marx

Dear Dr. Rudman,
I found some pictures on the web (what did we ever do without the web?) that resemble my nudi and call it Roboastra gracilis, but I am not totally convinced:

Although the general body form, colour pattern, rhinophore style and gill-style matches up, there are absolutely no yellow pigment and 4 gills, not 3 and the distribution does not match at all.

Locality: Ponta Malongane, Steps reef. Mozambique, Indian Ocean.
Depth: 10-12 m. Length: 30-35 mm. 8 February 2005. Very sandy patch in rocky reef. Photographer: Riaan Marx

Unfortunately the surge was horrible and I could not manage a better photo than this. I guess the question is - how common is morphological variations like this generally and specifically in this species?

Kind regards,
Riaan Marx

v-riaanm@microsoft.com

Marx, R., 2005 (Mar 3) Roboastra gracilis from Mozambique. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/13250

Dear Riaan,
It certainly falls within what I would consider the variation in this species. If you look at the other messages on the Forum the colour markings range from yellow to orange and can be either lines or spots or a combination. All 3 gills is common there are others with 4. Terry Gosliner [Nudibranchs of Southern Africa ] has a photo from Sodwana, South Africa, of an animal very similar in colour to yours

Most species show some variability in colour pattern, the trick is to work out by comparative anatomy and lots of material, just how much variation can occur in one species. That is one of the very valuable ways that amateurs, through the Forum, can help us learn more about these animals. There are many examples on the Forum of photos showing new colour variations in a species, and suggesting how perhaps 2 so-called species are in fact just colour forms of one. Photographs alone are not proof, but that certainly are a good way to guide scientists into asking the right questions.
Best wishes,
Bill Rudman

Rudman, W.B., 2005 (Mar 3). Comment on Roboastra gracilis from Mozambique by Riaan Marx. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/13250

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