Comparing Halgerda carlsoni & H.malesso

February 3, 1999
From: Erwin Koehler

Dear Bill,
Some days ago I sent a photo of Halgerda malesso to you, (Housereef, Lipayo, Negros Is., Philippines, Nov. 1998) identified according Deblius' book, but now I found several photos at WWW looking similar to mine, which are identified as H. carlsoni. Can you bring some light into my darkness and tell the differences between those similar looking species?

I don't want to get on your nerves, I'm very glad that I've found someone who answers to my questions...2 years ago I was a diver with a camera, who loved nudibranchs, nothing more. Now I think I know quite a lot more, I own several scientific books (but it's hard to understand them). I try to indentify the slugs on my photos by the pictures in these books, sometimes I try to understand the text (English/Latin is difficult, other languages are impossible).
Now to Halgerda:
In Debelius' book is a photo of H. carlsoni (black rhinopores, almost no orange ornaments), the same specimen (another photo) is in Clay Bryce's book. Other photos of H. carlsoni at http://siolibrary.ucsd.edu/slugsite/phil/carlsoni.html and at http://www.oz.net/~jrosenf/carlsoni28_nudis1.html are looking exactly like H. malesso at Debelius' book.
The photo of H. carlsoni at http://siolibrary.ucsd.edu/slugsite/nudiwkps/nudiwk1.html points to the top of my confusion - rhinopores like H. carlsoni and ornaments like H. malesso in Debelius' book.
Erwin

E.Koehler@deutschepost.de

Koehler, E., 1999 (Feb 3) Comparing Halgerda carlsoni & H.malesso. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/533

Dear Erwin,
Sorry I didn't post your pic earlier but I happily had too much to deal with all at once. Don't worry about sending questions etc. If I didn't want to answer them I wouldn't have started the website.

The orange and white species of Halgerda are confusing and I suspect there is more of the story yet to tell. The basic difference between H. carlsoni and H. malesso is that the first has a background of fine orange specks and the second a network of orange lines. The first two pictures you refer to:
http://siolibrary.ucsd.edu/slugsite/phil/carlsoni.html and http://www.oz.net/~jrosenf/carlsoni28_nudis1.html
are not H. carlsoni (even though they are labelled as such), but H. malesso.

The third picture at http://siolibrary.ucsd.edu/slugsite/nudiwkps/nudiwk1.html is probably H. carlsoni but I haven't seen a specimen with a solid orange mantle border before. It is like the border of Halgerda aurantiomaculata.

This doesn't totally solve your problem but I think it is the orange pattern, rather than the rhinophore and gill patterns which are important. It is possible that the uniform blackish colour of the gills and rhinophores of the last picture indicates it is a different species, but it may just be an aberrant colour form.
Best wishes,
Bill Rudman.

PS: See Clay Carlson's February 5, 1999 message comparing this species with the real H. malesso.

Rudman, W.B., 1999 (Feb 3). Comment on Comparing Halgerda carlsoni & H.malesso by Erwin Koehler. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/533

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