Another aquarium mystery

October 18, 2000
From: Robert Dahrling

I have discovered a nudibranch in my 29 gal. mini reef tank. It is only 1/2 to 3/4 inch long. It is lime green, but its antenna have white tips and the tip of it's tail is also white. It has short yellow bristles along it's dorsum. I find it a lot in macroalgae, especially Caulerpa. Can you identify it from this description and tell me if you think I have an herbivore or carnivore?


Dahrling, R., 2000 (Oct 18) Another aquarium mystery. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Rob,
You haven't given me any clues to where in the world your animal may have come from or much about its shape. However, since you say it is mostly green and prefers Caulerpa then you probbaly have a sacoglossan sea slug. Sacoglossans are all herbivores, sucking the sap out of the algae they feed on much like bugs suck the sap out of plants on land. They are sea slugs but they are not nudibranchs. They shouldn't cause any problems in your aquarium although they will eat a bit of Caulerpa.

Have a look at some of the species in the Species List in the Order Sacoglossa. A couple of possibilities would be a species of Oxynoe which still has a transparent shell, or a species of Elysia which are often green.

Best wishes,
Bill Rudman.

Rudman, W.B., 2000 (Oct 18). Comment on Another aquarium mystery by Robert Dahrling. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from


Oxynoe sp. 1

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