Risbecia ghardaqana
(Gohar & Aboul-Ela, 1957)

Order: NUDIBRANCHIA
Suborder: DORIDINA
Family: Chromodorididae

DISTRIBUTION

Red Sea, Indian Ocean.

PHOTO

UPPER: Musandam, nthn Oman, NW Indian Ocean. September 2000. Photo: Gordon T. Smith.
LOWER: Suakin, Sudan, Red Sea, 10m, May 1980, Photo: C. Todd.

This is one of a number of similarly coloured yellow-spotted species including Risbecia imperialis, Risbecia pulchella, and Chromodoris annulata.

Risbecia ghardaqana occurs sympatrically in the Red Sea, and probably elsewhere in the Indian Ocean, with Chromodoris annulata and Risbecia pulchella. Some confusion has existed on the Forum concerning the identity of the two species of Risbecia. See my message concerning this below. Gohar & Aboul-Ela (1957) reported on the anatomy and developmental biology of these three yellow-spotted chromodorids from Al Ghardaqa, on the Egyptian Red Sea coast,and it was in this publication that Risbecia ghardaqana was recognised a distinct species, which although very similar to the common Risbecia pulchella, differs in a few colour, anatomical and developmental differences. Rudman (1987) placed the species in the genus Risbecia.

Compared with R. pulchella which grows to approx 11cm, R ghardaqana only grows to approx 5.5cm long. The ground colour of the body is white and there are no violet tinged patches. The spots on the mantle and sides of body are yellow not orange and much fewer in number than in R. pulchella. The anterior end of the mantle is not produced into a prominent veil like R. pulchella and the mantle border is bright blue not violet. The gills are simple and although a few may bifurcate they are never as branched as in R. pulchella. They are non vibratile.' The egg-ribbon is white when newly deposited, and the eggs are arranged in one layer rather than two.

References:
• Gohar, H. A. F., & I. A. Aboul-Ela. 1957a. The development of three chromodorids (with the description of a new species). Publications of the Marine Biological Station, Al-Ghardaqa, Egypt, 9: 203-228, pls. 1-5.
• Rudman, W.B. (1984) The Chromodorididae (Opisthobranchia: Mollusca) of the Indo-West Pacific: a review of the genera. Zoological Journal of the Linnean Society, 81: 115-273.
• Rudman, W.B. (1987) The Chromodorididae (Opisthobranchia: Mollusca) of the Indo-West Pacific: Chromodoris epicuria, C. aureopurpurea, C. annulata, C. coi and Risbecia tryoni colour groups. Zoological Journal of the Linnean Society, 90: 305-407.

Authorship details
Rudman, W.B., 2003 (April 8) Risbecia ghardaqana (Gohar & Aboul-Ela, 1957). [In] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/factsheet/risbghar

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