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Bill Rudman writes at the Sea-Slug Forum:
"It ranges in colour from a pale straw, or even white background to a deep purplish pink. There is usually a thin opaque white line at the mantle border, but some specimens have a reddish purple border. Typically the gills and rhinophores are yellow or orange with a basal pink or purplish band. In anatomical studies I have been unable to find any consistent differences to show that differing colour patterns represent differnet species."
IPN distinguishes between Hypselodoris bullockii and various Hypselodoris sp. of the Hypselodoris bullockii complex at pages 267 and 268:
"It is light pink with a thin opaque white marginal line. The gills and rhinophores are white basally with reddish tips."
Gosliner, Terrence M., David W. Behrens & Ángel Valdés. 2008. Indo-Pacific Nudibranchs and Sea Slugs. Sea Challengers Natural History Books.
Gig Harbor, Washington. 426 pp.
None of the 4 Hypselodoris bullockii specimens in IPN has gills and rhinophores as described 'white basally', all are purplish at the base, not white.
NUDIPIXEL uses the name Hypselodoris bullockiii and follows IPN by distinguishing, let me quote the desciption: "Hypselodoris bullockii has several pale purple shade variations, from very pale, almost white, whitish purple to purple, but never as dark as the purple found in Hypselodoris apolegma. The colour is uniform over the whole mantle, with a narrow band of white or dark purple at the mantle edge. The gills and antennas are yellow with purplish base or pale purple all over."
I made the decision on 18 August 2011, to follow also IPN by distinguishing! I moved some specimens to the new Hypselodoris sp. 07, and created Hypselodoris sp. 08.
Pretty similar are:
Hypselodoris sp. 07 which differs by the light purple background colour, by the broad white marginal band, and by the colour of the gills and the rhinophores
Hypselodoris sp. 08 which differs by the dark purple background colour, by the broad white marginal band, and by the colour of the gills
Hypselodoris sp. 10 which differs by the dark blueish-purple colour of the rhinophore clubs, by the dark purple background colour, by the broad white marginal band, and by the colour of the gills,
Hypselodoris apolegma which differs by the purple colour, and by the reticulate white edging of the mantle.
Thorunna halourga which differs by the broad white mantle margin, and by the low gill pocket.
More information on Hypselodoris bullockii are on Bill Rudman's Sea-Slug Forum!