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I saw Pleurobranchus weberi before only at Mike Miller's Slug Site. It is characterised by a dark red background colour and many large 'white' double rings. I think these double rings are translucent, some kind of sticky mucus, the colour of them depends on the colour of the sand it is crawling on, white sand makes white rings, tan sand makes tan rings, etc. This is a very large sea-slug, it grows up to 20 cm.
More information on Pleurobranchus weberi are on Bill Rudman's Sea-Slug Forum!
How to cite:
Köhler, E. (2017), published 22 June 2017, Pleurobranchus weberi (Bergh 1905)
available from https://www.Philippine-Sea-Slugs.com/Pleurobranchomorpha/Pleurobranchus_weberi.htm