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Very similar are the juveniles of Roboastra luteolineata, which differ by a dark lines on the gills, and by yellowish-green markings between the rhinophores.
More information on Roboastra gracilis are on Bill Rudman's Sea-Slug Forum!
How to cite:
Köhler, E. (2016), published 30 March 2016, Roboastra gracilis (Bergh, 1877)
available from http://www.Philippine-Sea-Slugs.com/Nudibranchia/Euctenidiacea/Roboastra_gracilis.htm