"Both this species and Ceratosoma trilobatum have very great colour variation, so neither of them can be identified by colour alone. Fortunately the smooth ‘neck’ zone of Ceratosoma gracillimum (as against a continuous ridge in Ceratosoma trilobatum) is a consistently reliable way to distinguish between them."
Comment from Richard Willan
Both this species and Ceratosoma trilobatum have very great colour variation, so neither of them can be identified by colour alone. Fortunately the smooth ‘neck’ zone of Ceratosoma gracillimum (as against a continuous ridge in Ceratosoma trilobatum) is a consistently reliable way to distinguish between them.