Hypselodoris maridadilus & H. mouaci etc.

Dear Clay,
Your plaintive email jogged me into action.. although I wouldn't say that this will be the final word.

It looks to me that there are a pair of sibling species, one in the Indian Ocean (H. maridadilus) and one in the western Pacific (H. whitei). The major difference would seem to be the white upper (inner)edge to each gill and the white tip to the rhinophore in the western Pacific species. There is some colour variation in the western Pacific with specimens from the northern end of the range, Japan, Hawaii, Enewetak having a very opaque whitish background colour which is replaced further south by a series of opaque white or cream patches on a darker translucent background. I can't find distinctive differences in radular morphology.

Nathalie Yonow described a species, Hypselodoris centunculus from the Maldives in the eastern Indian Ocean. She describes white-tipped rhinophores, which are characteristic of H. whitei, but she describes the gills as orange, which is characteristic of H. marididalus. It is difficult from the accompanying photo to see whether there is a white edging to the upper (inner) edge of the gills, or whether the white tips to the rhinophores are a photographic artifact. At this stage I think we will need to wait for more material, or at least photos, to determine the colour variability across the eastern Indian Ocean. I have posted two pages, Hypselodoris maridadilus and Hypselodoris whitei, one for each geographic region. Any further photos gratefully received.

Bill Rudman.