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Very similar are:
Trapania aurata, which was my original identification of this specimen, it differs only by the dorso-lateral processes, which have an orange longitudinal band, and
Trapania cf. aurata, which differs by the orange longitudinal bands at the dorso-lateral processes, and lacks orange on the gills, rhinophores and at the posterior end of the foot.
Trapania cf. vitta, which lacks the orange middorsal line at the posterior end of the foot, and
Trapania gibbera, which differs by a dark brown bar between the oral tentacles.
Trapania sp. 08, which differs by brown/black tipped rhinophores, and by translucent white gills.
Trapania armilla, which differs by a tuberculate body, and by a thin dark brown ring on each oral tentacle.
More information on Trapania vitta are on Bill Rudman's Sea-Slug Forum!