Re: Unknown Dorid from Italy

October 12, 2009
From: Marina Poddubetskaia Ossokine

Concerning message #16985:

Dear Bill,

I can't identify the dorid in Dominique's message [#22563], but I think I can help with some other unidentified ones. To start, I think the dorid in message #16985 is Geitodoris planata.

Geitodoris planata is probably the most common nudibranch of Arcachon Bay, I saw so many of it. It is very variable in colour (creamy white, yellow, pale and dark brown) and in 'granularity' (low or obvious tubercles, with or without stellate pattern and acid glands). The underside of the mantle can have dark spots or not, at least some spots aren't visible with naked eye.

But all the Geitodoris planata have small yellow spots ringed in brown, like in this animal. Usually, these spots are hardly visible in field photos, but always present if you check it with binocular microscope. I have included close-ups in the upper photo showing yellow and brown colour forms.

The middle photo shows an animal with only one acid gland but yellow spots visible in field. I haven't seen these spots in other similar dorids. And the egg-mass of Cristian's message fits this species.

To complete the colour variation in G. planata, the lower photo shows the creamy white colour form.

Upper Photo: Locality: 'Le Mimbeau', Cap Ferret, Arcachon Bay, 7 m, France, Atlantic Ocean, 8 May 2006. Length: yellow 20mm + brown 27 mm. Photographer: Marina Poddubetskaia.

Middle Photo: Locality: 'St-Yves', Arcachon, 12 m, France, Atlantic Ocean, 29 June 2005. Length: 35 mm. Photographer: Marina Poddubetskaia.

Lower Photo: Locality: 'Le Mimbeau', Cap Ferret, Arcachon Bay, 7 m, France, Atlantic Ocean, 8 May 2006. Length: 43 mm. Photographer: Marina Poddubetskaia.

Best wishes,
Marina.

nembro@yahoo.fr

Poddubetskaia Ossokine, M., 2009 (Oct 12) Re: Unknown Dorid from Italy. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/22693

Dear Marina,

Thanks very much for these photos showing variation in the species and identifying Cristian's animal. Finding someone who knows a local fauna well is usually the best way to resolve these identification puzzles. Most books emphasise the white stellate pattern around the acid glands which as you show is not very useful for animals which lack the pattern

Best wishes,
Bill Rudman

Rudman, W.B., 2009 (Oct 12). Comment on Re: Unknown Dorid from Italy by Marina Poddubetskaia Ossokine. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/22693

Factsheet

Geitodoris planata

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