Re: Phyllidiella zeylanica from Indian Ocean

March 11, 2009
From: Sandrine and Hugues Flodrops

Concerning message #17730:

Dear Bill,
Always the same question between Phyllidiella zeylanica and P. rosans? I hope this time that we found our first P. zeylanica in Mayotte. The two specimens have compound tubercules, the only discussion is about the number of pink ridges. Is the number of pink ridges a good character to differentiate the two species? Up to nine in P. zeylanica and six to nine in P. rosans.

Locality: Upper photo: Pointe Barracuda "Passe en S". Mayotte. Indian Ocean. Depth: 18 metres. Specimen length: about 35 mm. 2 March 2009. Lower photo: Balcon sur le Bleu "Passe en S". Mayotte. Indian Ocean. Depth: 20 metres. Specimen length: 35 mm. 4 March 2009. Photographer: Hugues Flodrops.

Thanks for your expertise.
Regards.
Sandrine et Hugues.

hugues.flodrops@wanadoo.fr

Flodrops,S. H., 2009 (Mar 11) Re: Phyllidiella zeylanica from Indian Ocean. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/22321

Dear Sandrine and Hugues,

According to David Brunckhorst, The main way to differentiate these two species externally is not the number of ridges but whether the ridges are smooth or not. In P. zeylanica the ridges are usually rough and nodulose, as in your two animals, while in P. rosans the ridges are relatively smooth with no real sign of underlying pustules. Another external character is that the foot of P. zeylanica is whitish and its gills and oral tentacles are dark grey while in P. rosans all the underside is pale grey.

David Brunckhorst's review was the result of a diligent and exhaustive study of both existing collections and material that he collected from a wide variety of localities. However no taxonomic work is ever totally complete, and one way of testing taxonomic decisions is to study large populations of animals at particular places. You are developing a good knowledge of your local population. If your experience suggests that P. zeylanica and P. rosans are just extreme forms of the same species then let us know. Do Brunckhorst's ventral colour differences agree with your observations? Have you found intermediates between the two species? Local experience can be of great value in showing us where taxonomic problems still exist.

Best wishes,
Bill Rudman

Rudman, W.B., 2009 (Mar 11). Comment on Re: Phyllidiella zeylanica from Indian Ocean by Sandrine and Hugues Flodrops. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/22321

Factsheet

Phyllidiella zeylanica

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