Here are a few pictures of a mysterious slug that I was very surprised to find one night roaming around in my tank. It must have hitched it's way into the reef on a piece of live rock or a coral. I estimate that it has been in my tank for approximately one year.

It is all black except for the base of it's "foot", which is the typical snail/slug fleshy color. The body of the slug is covered by a soft frilly mantle. It has a small white slit in the middle of the mantle. I suspect this is part of shell that is exposed. Overall it is about 2.5" in length and a bit less in width, although it is almost round. It has two (2) antennae that are somewhat visible in one of the pics.  

This slug is very nocturnal, never venturing out in the open during lights-on. It appears to graze on the various types of algae that grow on the glass and other surfaces in the tank. I once suspected that it was feeding off of the copious amounts of sponge that grows on the undersides of the rocks, but I now question that theory; I doubt that the growth of the sponge could keep up with the predation, but I may be wrong. I know for certain it is not preying on anything desirable in the tank. 

With the help of other reefers on the NET, I have identified this creature as the limpet, Scutus unguis, from the Indo Pacific. It is also known as the Hoof-Shield limpet. It is listed as omnivorous, but reports indicate that it feeds mostly on detritus and algae in the aquarium. This makes this hitchhiker a welcome addition to any reef aquarium. I have not been able to find information on it's lifespan or growth patterns. I suspect mine is full size, or close to it.

I would really appreciate any other information you can provide, whether factual or anecdotal. You can feel free to e-mail me the information or any questions you may have, or you can sign my Guest Book and leave any comments there.