Nudibranch in reef tank

January 4, 1999
From: Eirik Mack Eilertsen

This might be a bit out of the ordinary, but I've tried posting my question through aquarium related channels with no luck.
While looking into my reef tank with a flashlight one night, I stumbled across a big (1"), white opistobranch that seemed to be busy laying eggs in chains consisting of sausage shaped egg containers. The animal itself seems almost transparent white with snow white branched, feathery gills arranged in two lateral lines.

Enclosed are some simple drawings of what the animal looked like, with an additional close up view of one of the animals two tentacles. They did seem rather special to me, and might help you to ID the animal. The gills are more branched/feathery than what thy look like in the picture and is the overall striking feature of the animal.

Anything you can tell me about these animals would be greately appreciated. Quite a few nudibranchs are known to do inflict damage to corals and polyps, and most aquarists (although none of them able to ID the animals) told me to get rid of them. Personally I like them, and if possible would very much like to keep them.

The animals must have been introduced with corals shipped from Indonesia. If anyone knows what it could be and how I can best care for it, I would be grateful.

Thanks in advance.

Eirik Mack Eilertsen

Norwegian College of Fisheries Science
University of Tromsoe,

Eilertsen. E.M., 1999 (Jan 4) Nudibranch in reef tank. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Eirik,
Your drawings show all the characteristic features of a family of nudibranchs called the Tritoniidae. The rhinophores (head tentacles) have a ring of papillae around a central core which is unique to them. I can't be 100% certain but I suspect your animal is Tritoniopsis elegans. Have a look at the photos I have posted at the top of this page. When large their gills becomes large and expansive and give the body a flattened lace-like appearance. However, up to about the size of your animal, they have a more erect shape as you have drawn.

Whether you have this species or not, they will not eat hard corals but do feed on soft-corals, and it seems that most species have a fairly specific diet. Tritoniopsis elegans usually feeds on Lobophyton but has been recorded on other soft-corals such as Spongodes. If you have soft-corals in your aquarium it may find one to its liking. I would think you would notice if it was causing damage as it will only eat a bit at a time. If you haven't soft-corals it won't eat your hard corals. If that is the case then unfortunately it will gradually die of starvation. My feeling would be to let it live out its last days in the relative sanctuary of your aquarium.

Best wishes,
Bill Rudman.
PS. Please let me know if I guessed right?

Rudman, W.B., 1999 (Jan 4). Comment on Nudibranch in reef tank by Eirik Mack Eilertsen. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

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