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Very similar is Phidiana militaris. They can be distinguished by the line between the rhinophores: Phidiana indica has a white line, Phidiana militaris has an orange or red line.
Bill Rudman writes: Phidiana indica is "also placed in the genera Learchis, Caloria, Hervia and Facelina by various authors. The correct generic placing cannot be resolved at present."
More information on Phidiana indica are on Bill Rudman's Sea-Slug Forum!