Reticulidia halgerda  Brunckhorst & Burn in Brunckhorst, 1990

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Reticulidia halgerda is characterized by numerous, narrow yellow ridges and an orange mantle margin. Pretty similar is Reticulidia fungia which has fewer, large yellow ridges with a fine white border and a broad blue-grey mantle margin.
More information on Reticulidia halgerda are on Bill Rudman's Sea-Slug Forum!