Nudibranchs in Symbiosis with Zooxanthellae

November 9, 1998
From: J.E. Austin

3 November 1998
Dear Dr. Rudman:
First, I want to thank-you for responding to my last questions and praise the exciting images located on the slug site. I have spent all night reading these pages. As I mentioned, I am an undergrad from Florida State University in the US and am involved in a Research Experience for Undergraduates. On Wednesday, I will join a deep-water boat cruise off of the south coast of Bermuda. I hope to dip net Sargassum and find the Sargassum nudibranch, so I'll keep you posted on my findings. :)
I have been watching Hypselodoris nudibranchs that were gathered outside the Bermuda Biological Station. They sit in my flow-through tank and have laid ribbons with red eggs. Some of them have little purple nodules beneath the side flaps of tissue. They are beautiful and hungry, I think.
I've been thinking of algal symbiosis again as I'm reviewing literature on chemical communication between algal endosymbionts and cnidarians. The mechanisms for mutual responsiveness have yet to enumerated. It seems- given the widespread independent evolution of symbiosis with algal cells- we'd have more answers. But instead, I'd like to please ask some more questions. :)

Concerning: Kempf, S.C. 1984. Symbiosis between the zooxanthellae Symbiodinium microadriaticum and four species of nudibranchs. Biol. Bull. 166: 110-126.

1) Do you know whether further Hawaiian species of Melibe have been described and whether a phylogeny exists for the Genus?
2) With the intent of raising nudibranch eggs, can one just keep them in a bowl with an aerator? How would one know if they've hatched, what to feed them?
If I wanted to do a time series to capture structure over an age range, can I just preserve them in SW 10% Formalin, then slide mount samples?
3) Is there a general use stain for sea slug tissue? I'm leaning toward neurons.
4) The paper indicates that the aeolid Berghia major has an oral veil. And I know that Melibe species do, has this morphological attribute been derived independently in other nudibranchs? Have any further observations on Melibe pilosa feeding been made since the Kempf paper; another food source beyond just captured crustaceans in the oral veil, i.e. some algal cell-containing prey?

Concerning: Rudman, W.B. 1991. Further studies on the taxonomy and biology of the octocoral-feeding genus Phyllodesmium, Ehrenberg, 1831 (Nudibranchia: Aeolidoidea). J. Moll. Stud. 57: 167-203.

1) As Phyllodesmium can autotomize ceras that contain antifeedant chemicals, have the actual compounds responsible been isolated or characterized? How would the anti-feedant nature be characterized- fed to fish?
2) The paper mentions that Chromodorids can concentrate anti-feedants from consumed sponges. Has this been assayed in Hypselodoris zebra? This orange, blue-striped dorid found in Bermuda feeds on the purple sponge Dysidea etherea?. I have 6 specimens and would like to try something, any suggestions?
3) The paper makes reference to Rudman 1984, but I could not find the reference at the end and was wondering if you have that citation?

Thank-you for your time,
J.E. Austin

Austin, J.E., 1998 (Nov 9) Nudibranchs in Symbiosis with Zooxanthellae. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear "j.e.",
Your obviously have been doing some thinking and reading! Sorry I can't answer all your questions at once, but in the hope someone out there has something to say on any of your points I am posting your questions unanswered. .. and will get to them in the next few days.

I hope you find some some animals in the Sargassum. If you have the facilities to photograph anything you find, including Hypselodoris zebra, I would love to post them on the Slug Forum. If you can't provide scans that is no problem. Just send photos or slides to me at:
The Australian Museum,
6 College St
Sydney, NSW 2000

I will scan them here and return the photos to you.

Best wishes,
Bill Rudman.

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