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Pretty similar is Madrella sanguinea (Angas, 1864) [Janus] which seems to be endemic to South East Autralia, though there are some records from Japan, and differs by a bright orange colour and is usually smaller, it seldom grows longer than 15 mm. Both species exude a yellow, possibly defensive secretion from a gland at the base of each ceras.
Gosliner, Terrence M., David W. Behrens & Ángel Valdés. 2008. Indo-Pacific Nudibranchs and Sea Slugs. Sea Challengers Natural History Books.
Gig Harbor, Washington. 426pp.
More information on Madrella ferruginosa are on Bill Rudman's Sea-Slug Forum!
How to cite:
Köhler, E. (2016), published 24 November 2016, Madrella ferruginosa Alder & Hancock, 1864
available from https://www.Philippine-Sea-Slugs.com/Nudibranchia/Cladobranchia/Madrella_ferruginosa.htm