Juvenile Flabellina ischitana vs F. pedata

May 30, 2007
From: Dominique Horst

Hi Bill,

I have also difficulties to make a distinction between Flabellina pedata and Flabellina ischitana, especially for juveniles.
For adult specimens, rhinophores are very different and is a criteria of choice to distinguish the two species : F. pedata rhinophores are wrinkled and are ringed or circled in F. ischitana.

Locality: Cap d'Antibes, 20 m, France, Mediterranea, 23 August 2006, rocks. Length: 10 mm. Photographer: Dominique Horst.

But, when having juveniles like on pictures, the task is not easy ... I've a suggestion about the position of the cerata. For F. ischitana cerata are arranged in kind of cluster and for F. pedata the cerata are more in spaced ranks.
Not sure that this criteria is robust...

Any suggestion would be very appreciated.
Many thanks for your help
Best regards,
Dominique

dominique.horst@wanadoo.fr

Horst, D., 2007 (May 30) Juvenile Flabellina ischitana vs F. pedata. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/18473

Dear Dominique,
I'm afraid I am not much help with the subtle differences between juvenile Flabellina. Sometimes if you have juveniles of similar species together in the field the differences appear quite obvious, but if you have only one species at a time the differences tend to disappear. However I would suspect an animal that was going to have ridges or rings or papillae on its rhinophores would have started to develop them by the time it was 10 mm long. Adult F. ischitana and F. affinis both have their cerata arranged on common 'trunks' or bases, while in F. pedata the cerata are arranged in rows, with each ceras separately inserting into the body wall. This would correspond with your suggestion that juveniles of F. pedata and F. ischitana would differ in ceratal arrangement. I suspect your animals here are all F. pedata.

My biggest problems with identifying your beautiful 'purple' Flabellina are between F. affinis and F. ischitana. Despite my best efforts I suspect some of the photos in the Forum are still misidentified.

Best wishes,
Bill Rudman

Rudman, W.B., 2007 (May 30). Comment on Juvenile Flabellina ischitana vs F. pedata by Dominique Horst. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/18473

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