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Very similar are
Dendrodoris fumata which can externally be distiguished by the shape of the body when crawling: Dendrodoris nigra is more elongate. Another feature is the position and nature of the gills: In Dendrodoris nigra the gills are relatively numerous and form a compact circle around the anus at the extreme posterior end of the dorsum. Dendrodoris fumata has 5 or 6 large branching gills which often spread from one side of the mantle to the other and are situated in some distance from the extreme posterior end.
Dendrodoris arborescens which has no white spots and a marginal orange/red band.
More information on Dendrodoris nigra are on Bill Rudman's Sea-Slug Forum!
How to cite:
Köhler, E. (2017), published 17 March 2017, Dendrodoris nigra (Stimpson, 1855)
available from https://www.Philippine-Sea-Slugs.com/Nudibranchia/Euctenidiacea/Dendrodoris_nigra.htm