Need some advice - uninvited aquarium guests

December 30, 2002
From: Jenifer

I am starting a 55 gal salt tank, and have only put live rock, an urchin, and a crab in it to start my filters. Recently I have noticed literally millions of eggs all over my Caulerpa and on the sides of my tank. The eggs are yellow and are in clusters all over. I have only had my tank up for about 2 weeks, and noticed 2 slugs that look like they are possibly Elysia papillosa. Do I need to be concerned about all the eggs, or just let them be. I don't want to let this get out of hand before I get started on my salt adventure.
One "slug" is a brilliant green and the other is a lighter lemon yellow. Both are quick movers, and have 2 lines of "spines" down their upper body and they join into one line down their "tail." I have seen them hang suspended from the water's surface by a "slime" string. Any hints, clues, or suggestions would be greatly appreciated.

Dear Jenifer,
I would need a photo of the slugs and the eggs - or a reasonable drawing - before could say anything sensible about your animals. Your mention of 'spikes' on the back sound more like a species of Elysia or Placida rather than an Elysia. Whatever you have the eggs are only likelt to cause a population explosion if the larvae hatch, and if they do hatch, they need to survive and develop into slugs. Most sea slugs have larvae that spend some time swimming in the sea feeding on microscopic plants. These larvae are very difficult to keep alive in aquaria. However there are a few species, such as Elysia crispata, whose larvae do survive in aquaria, much to the delight of their owners [see Joe's recent message].

I am afraid without further clues, I can't give you much advice. Perhaps a photo, or some idea where in the world the Caulerpa came from would be a help. My advice would be to wait and see what happens. It could be interesting. I don't know of anyone whose tank has been over run by a sacoglossan sea slug so you are unlikely to end up with a major problem.
Best wishes,
Bill Rudman

Rudman, W.B., 2002 (Dec 30). Comment on Need some advice - uninvited aquarium guests by Jenifer. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

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