Polyp-feeding nudibranch

December 7, 2002
From: Mark Johnson

I bought some Caulerpa prolifera algae and it came on a piece of Live Rock with all kinds of critters and algae as well as a small colony of button polyps. Anyway I have had this for about 2 weeks now and all of a sudden I noticed my button polyps closing up and after 2-3 days noticed this little critter crwling on it. Upon closer inspection and a little research thanks to this site it seem to be some sort of a Nudibranch. I found a photo of Berghia verrucicornis that looks very similar except mine is totally brown with a light brown body. It is the exact same color as my brown polyps and its spikes on its back are the same size and shape as the tentacles on my brown button poly. I read that they eat Aiptasia and was wondering if they eat brown button polyps as well. It crawls on the polyps but doesn't seem to be causing any physical damage but it keeps the polyps from opening and I'm afraid they will starve. Or when/if the Nudibranch gets bigger it will start harming them.
Mark Johnson


Dear Mark,
Your animal certainly looks like an aeolid nudibranch but it may be a species we don't know about. Most aeolids feed on cnidarians of some sort, some specialising on hydroids, some on sea anemones, or hard corals or sift corals. Most are very specific in their food choice. I am not sure what species your 'button polyp' is, but it looks quite like the one in a recent message, which was also being eaten by a nudibranch. Since we don't know what your slug is, I can't give you any advice on how 'dangerous' it is. However since you bought the live rock for the Caulerpa the button polyps and the nudibranch are a bonus. I am biased, but my advice would be to let 'nature' take its course, and just see what happens. It is possible the aeolid has quite a bit of growing to do. If so, we would have a much better idea of its identify if it were allowed to grow a bit bigger, and unless you find you have an invasion of these slugs, I doubt it will do much damage to the polyps.
If you are brave and leave it alive, I would be intersted in some followup information in a few weeks and some photos
Best wishes,
Bill Rudman

Rudman, W.B., 2002 (Dec 7). Comment on Polyp-feeding nudibranch by Mark Johnson. [Message in] Sea Slug Forum. Australian Museum, Sydney. Available from http://www.seaslugforum.net/find/8581

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