Hypselodoris maridadilus Rudman, 1977
Nudibranchs of the genus Hypselodoris are often marked with longitudinal lines. This slug is a good example. Parallel magenta stripes run the length of its delicate white body. The rhinophores and gills are orange with white tips. In Hawai`i it is known primarily from protected locations where it is occasionally seen by day crawling in the open. Most Hawaiian specimens have been collected from the lagoon at Midway Atoll. The species attains about 1 inch and is recorded from the East Africa, Madagascar, Seychelles, Western Australia, Japan and Hawai`i. It was described from East African specimens and the name derives from “maridadi,” the Swahili word for “beautiful.”
There is controversy over the identity of the Hawaiian and Japanese animals. Bill Rudman points out in his Sea Slug Forum, that specimens of H. maridadilus from the Western Indian Ocean lack the white tips on the gills and rhinophores and have a yellowish rather than white ground color. He identifies all “maridadilus” type nudibranchs from the Pacific as H. whitei. Terry Gosliner, however, considers animals from Japan and Hawai`i to be the true H. maridadilus because they lack pustules between the lines. To a non-expert like myself, pictures of the Hawaiian slugs certainly look more like H. maridadilus than H. whitei. On the other hand, Rudman himself described H. maridadilus in 1977, so he ought to know. As Mike Miller would say, “Isn’t slugging fun!”
Photo: My dive buddy Dan Dickey found these two while we were diving along the side of the boat channel at Ala Moana Beach Park in Honolulu--a site commonly called "Magic Island." Magic it proved to be that day. Depth was about 15 ft.
Hawaii's Fishes, a Guide for Snorkelers, Divers and Aquarists Mutual Publishing, 1993
Hawaii's Underwater Paradise, Mutual Publishing, 1997
Hawaii's Sea Creatures, a guide to Hawaii's Marine Invertebrates. Mutual Publishing, 1999.
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