Ceratosoma trilobatum (J.E. Gray, 1827) [Doris]

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Ceratosoma trilobatum is characterized by 3 lobes as the name tells (tri = 3; lobatum = lobes): one on each side just anterior to the gills and one long recurved dorsal 'horn' behind the gills. There is usually a ridge joining each lateral lobe to the anterior head lobe. It is highly variable in the background colour.
Pretty similar are:
Ceratosoma tenue which can have very similar colour patterns but has 4 lateral lobes and one lobe behind the gills (5 lobes) and
Ceratosoma gracillimum which also has 3 lobes but no mantle edge between the head and the lateral lobes.
More information on Ceratosoma trilobatum are on Bill Rudman's Sea-Slug Forum!
How to cite:
Köhler, E. (2017), published 17 February 2017, Ceratosoma trilobatum (J.E. Gray, 1827)
available from https://www.Philippine-Sea-Slugs.com/Nudibranchia/Euctenidiacea/Ceratosoma_trilobatum.htm