Risbecia ghardaqana? from the Red Sea

July 24, 2006
From: Kamal El Tawil


Dear Bill,

Here is a beautiful Risbecia from the Red Sea crawling on coral formations. Is it R. pulchella or R. ghardaqana? The difference is still confusing for me. I turned to your message #9625 and my message #14651. Taking into consideration the nine gills on this nudibranch I identify it as Risbecia ghardaqana.

Locality: Maksour Reef, Fury Shoal, Red sea, 18, Egypt, Red Sea, 10 July 2006. Length: 50-60 mm. Photographer: Kamal El Tawil.

please confirm.
best regards,
Kamal

kamal@coralworld.net

El Tawil, K., 2006 (Jul 24) Risbecia ghardaqana? from the Red Sea. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/17209

Dear Kamal,

Firstly I am also confused by these two species. If it were not that Gohar & Aboul-Ela (1957) had examined so many specimens and could see clear differences, I would probably have concluded the two were variants of the same species. So I am as keen as you are to find more animals which fit there description of R. ghardaqana. It would also be nice to find egg ribbons of both species, as they note that R. ghardaqana has a white egg ribbon and R. pulchella a red-orange one.

Certainly the small number of gills, and the relatively large yellow spots in your photo, both fit their R. ghardaqana. However they state that the gills in R. ghardaqana are 'non vibratile', that is they don't wave from side to side, and that the front of the mantle doesn't expand into a 'prominent veil'. In your photo the front of the mantle does expand, and the gills certainly look as though they are waving around.

The record on the Forum I am most comfortable with is Barbara Phua's from Thailand #7195. It is a long way from the Red Sea, but it seems the distribution of quite a few species extends across the nthn Indian Ocean from the Red Sea to Thailand. Her animals have few gills, no expanded region at the anterior end of the mantle, and lays a white egg ribbon. I can't be 100% sure, but I think your animal is a relatively small R. pulchella.

Please don't lose interest in this quest. Now that you are familiar with R. pulchella, hopefully when you do find R. ghardaqana, the differences will be obvious.

Best wishes,
Bill Rudman

Rudman, W.B., 2006 (Jul 24). Comment on Risbecia ghardaqana? from the Red Sea by Kamal El Tawil. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/17209

Factsheet

Risbecia pulchella

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