New pattern of Halgerda formosa? from Reunion Island

August 18, 2007
From: Hugues Flodrops

Dear Bill,
I found this specimen of Halgerda few days ago. I think it is H. formosa because there is one black spot on the front of the mantle. But we can observe some differences: there is no black line on the rhinophore stalk and the upper half of each gill seems to be entirely black. So I can't tell if it is Halgerda formosa, or perhaps a variant of Halgerda toliara or a new species.

Locality: Etang-Salé Permanent Pool, 0,8 m, Reunion Island, Indian Ocean, 5 august 2007, Early morning. Length: 18 mm. Photographer: Hugues Flodrops.

Like usually, thanks for your help.
Regards.
Hugues

hugues.flodrops@wanadoo.fr

Flodrops, H., 2007 (Aug 18) New pattern of Halgerda formosa? from Reunion Island. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/20448

Dear Hugues,
Let us hope that your third suggestion - a new species - is not true. We have enough Halgerda names to sort out at present. I think the colour differences in the gills and rhinophores that you mention are of great importance, but we don't know enough about juvenile colour patterns to know whether the absence of the black marks on the rhinophore stalks and the black colour on the gills is a result of the small size of this animal. On the surface I would suggest H. toliara is the easy answer, but I don't know of any that have black spots on the mantle. In the upper photo it looks like there is the start of a black line of the right rhinophore stalk which would suggest it may be a juvenile still developing its colour pattern.

I think its best to tentatively identify this as H. formosa.

Best wishes,
Bill Rudman

Rudman, W.B., 2007 (Aug 18). Comment on New pattern of Halgerda formosa? from Reunion Island by Hugues Flodrops. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/20448

Factsheet

Halgerda formosa

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