How to study a nudibranch?

October 28, 1999
From: Phanor Montoya

Now that I have identified the Nudibranch (Dondice occidentalis Engel,1925)), I want to study its anatomical characteristics: nervous system, digestive system, reproductive apparatus, Etc. Unfortunately the information that I have on this topic is very poor. It would be possible that someone could recommend some books where to find drawings of these structures; how to isolate and study them; appropriate dissection kit. Which substances should be used to fix and to preserve nudibranchs in the laboratory? Finally, where can I find keys to Caribbean, Bahamas and Florida nudibranchs?

Thank you for the collaboration that you can give me.

Phanor Montoya
Student of Marine Biology
Santa Marta, Colombia

Montoya, P., 1999 (Oct 28) How to study a nudibranch?. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Phanor,
I'm afraid to find books with detailed anatomical drawings of nudibranchs you would need to go back to old works from last century. One volume which may still be available, which has excellent anatomical illustrations is:
McFarland, F.M. (1966). Studies of Opisthobranchiate Mollusks of the Pacific Coast of North America. memoirs of the California Academy of Sciences, Vol. IV.

I don't know if copies are still available, or how much they would cost, but Dr Terry Gosliner, who is at the California Academy of Sciences may be able to let you know.

A good source of information on mollusc phylogeny and anatomy, and the most comprehensive and up to date work would be:
Beesley,P.L., Ross,G.J.B. & Wells,A (eds) 1998. Mollusca: The Southern Synthesis. Fauna of Australia, Vol 5.. CSIRO Publishing : Melbourne. Part A pp1-563. Part b pp 564-1234. The opisthobranch section is in Vol 1. [I must declare I was involved in writing parts of it, but it is generally accepted as the best around at the moment]. It is however, quite expensive.

If you are planning a career in biology then you will probably need to build up a collection of research papers either by photo-copying articles from journals or by writing to research workers.

Concerning appropriate dissecting equipment, I think you should talk about this with your university teachers who will have a better idea of what is available. I do most of my work with fine forceps, fine scalpel, opthalmological scissors, and entomological pins, in a dish with a layer of wax into which the pins can be pushed to hold the animal during dissection. The other thing you will need is a good dissecting (binocular) microscope.

Luckily with nudibranchs, much of the the organ system lies free in the body cavity, so dissection is often a process of gradually untangling ducts rather than dissecting structures out of muscle or connective tissue. The unlucky part is that many nudibranchs are often very small.

Preserving and fixing specimens.
The first step is to narcotise the animals so they don't contract into an unrecognisable ball when placed in preservative. Two commonly used techniques are menthol crystals and magnesium salts.
Menthol crystals Put slugs in a shallow dish and float crystals on the surface of the sea water. It may take some hours for this method to work.
Magnesium salts Make a saturated solution of Magnesium chloride or Magnesium sulfate, and gradually add to seawater. This is a much quicker method and if you add carefully can give a good result.

I'll just mention the two common methods for general anatomy. For histology and DNA work more specialised techniques are required.
Formalin. I fix my material in 10% formalin overnight then transfer to 5% formalin for longterm storage. Formalin fumes can be unpleasant and it can sting if you have cuts on your hands. During dissecting I transfer the animal to water so that I don't breathe in the formalin fumes.
Alcohol. Many workers store their material in 70% alcohol (usually ethanol). Two disadavantages I find, are that it hardens reproductive structures so they are difficult to untangle, and if the specimen is dissected in water, mucus glands when broken or cut begin to rapidly swell and can completely obscure the dissection. For some reason the hardening does not seem to happen with land snail specimens.

I can't say whether alcohol or formalin is best, both work quite well.

The most important point is to photograph specimens alive, and if possible draw them and make colour notes.

Concerning 'keys' or 'guides' to opisthobranchs of your region. Sorry, but nothing has changed, to my knowledge, from my earlier answer and Anne Dupont's message. If you can send me a photo I am sure someone will be able to help you.

Best wishes,
Bill Rudman.

Rudman, W.B., 1999 (Oct 28). Comment on How to study a nudibranch? by Phanor Montoya. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

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