Halgerda toliara or H. formosa from Madagascar

September 18, 2002
From: Lindsay Warren


Note added 7 January 2004. This is almost certainly a form of H. wasinensis. See relevant discussion.

Dear Bill
I found several interesting opisthobranchs while diving around Nosy Be and Iles Mitsio off the northwest coast of Madagascar earlier this year. One of the finds was this Halgerda which is a bit of a puzzle. I found it on 24 January 2002 at about 8.30am at a depth of 54ft
while diving in the area of La Grotte, Ile Sakatia, NW Madagascar. L: 20mm.
Photos: Lindsay Warren.

I have checked through all the Halgerda on the Forum and the closest I could come to an ID is H. toliara. However, in your comments you mention that the viscera of this species are white while that of the one I found are black and that this is characertistic of H. formosa. However, the species I found does not have the black spots on the mantle which are characteristic in H. formosa but rather small white pustules on the mantle margin. The base of the branchial plume is translucent white with the upper half completely black as are the rhinophores, which is closer to H. toliara rather than H. formosa. What are your thoughts on this?
All the best
Lindsay

alldcl@compuserve.com

Warren, L., 2002 (Sep 18) Halgerda toliara or H. formosa from Madagascar. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/6223

Dear Lindsay,
Basically we still have much to learn about variability in these species. Whether the lining of the visceral cavity is black or translucent white seems to be a species specific character so its presence here would suggest your animal is closer to H. formosa than H. toliara. Another character used to distinguish these 2 species is the nature of the small tubercles around the mantle edge, translucent white in H. formosa and yellow in H. toliara. In your animal they are clearly translucent white. I agree there are no black spots on the mantle and the rhinophores lack some of the 'normal' colour pattern of H. formosa, but I think it is closer to that species than H. toliara. However what we clearly need is more local knowledge of this species group in the western Indian Ocean.
Best wishes,
Bill Rudman

Rudman, W.B., 2002 (Sep 18). Comment on Halgerda toliara or H. formosa from Madagascar by Lindsay Warren. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/6223

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