Phyllidia varicosa, dying?

May 11, 2002
From: Jeff Lockwood

Ok, now it seems I have a problem.
1st a few questions, the guy at the shop sold me a Phyllidia varicosa (my mistake not reading up first). He told me that this was not a nudibranch, but a sea cucumber... is this correct? I looked it up and it says that it is a rough-nobbed sea slug, and I know its Phyllidia varicosa. This same guy also told me that this species did not eat anything in particular but would feed off the particles floating around in the water. I did not belive this because of way these things are built, it looks like they crawl on something and eat it, not catch it out of the air, so a looked here and it seems that these guys eat sponges. So with that, I was wondering if there was a particular sponge this guy would like to munch on? Now I read many other question, and I know that people ask this question over and over again, so I didn't want to waste your time so I looked up "feeding" but I found nothing for this particular guy. The reason I ask is because I have a brown sponge (which I don't know the type) on a rock in my tank and I would be glad to give it up to the slug for food(its not as pretty) but I didn't know if he would like it, so my question is should I bother the little guy and actually place him on the sponge?

Now, why I am worried is because for the last week he has spent at the top of the tank, and he also just laid a 4 ringed, perfect spiral batch of eggs, and you said earlier that this could be a last attempt to keep his species going or something. These eggs might actually be fertile because it was sitting right next to another one in the tank when I got it. So to make it short and sweet:
Is it a nudibranch or sea cucumber?
Is there any sponge you can recommend that I get it for food?
Should I place it on my brown sponge?
Is there any way you would recommend me roping or closing off the eggs from other fish and the filter/powerheads?
and also Would you like a picture of the egg spiral or the slug? it seemed like you liked pictures, you have quite a bit.

Well, thank you for your time and I am sorry for taking so much of it as I am sure you have answered these questions many of times, but you seemed quite knowledgeable and I don't want to lose my little guy so I had too.
Thank you very much...

Lockwood, J., 2002 (May 11) Phyllidia varicosa, dying?. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from

Dear Jeff,
I would very much like a photo of the animal and its egg ribbon. We know so little about these animals that a photo of an animal with its egg ribbon would be quite a useful piece of information - and would mean it life was worthwhile - if rather abbreviated.
There is no harm in seeing if it will eat your brown sponge but I doubt it. One thing to be careful of with phyllidias in aquaria is that they can exude nasty poisons which kill fish and other life in aquaria. I suspect if it hasn't already done so it is unlikely to at this stage - probably no energy left to produce the chemicals. Concerning the eggs. They may hatch into microscopic free-swimming larvae but they feed on microscopic algae (phytoplankton) which I am sure you won't have in your aquarium so will almost certainly die. Even if you did successfully keep the larvae alive, they need their adult food sponge to trigger their change from larvae to crawling slugs so again not much joy.

Concerning your other questions. They are not Sea Cucumbers although there is a message on the Forum with a photo of one juvenile sea cucumber which mimicks the shape and colour of Phyllidia varicosa.
Best wishes,
Bill Rudman

Rudman, W.B., 2002 (May 11). Comment on Phyllidia varicosa, dying? by Jeff Lockwood. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from


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