Can anyone ID this?

[leslie]

Ok, I have this black thing in my tank (Center of photo.) It's about the size of a quarter, moves like a snail, is flat and slightly transparent. It's sides ripple like a stingray does. I've seen it 5 times in the last month and each time in the evening right before the lights go out.

Any ideas?

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[leslie]

And the "it's" should be "its."

 

[derek_s]

That is a sponge. It is good and will spread, but shouldnt ever become a nuisance. Some say it is a sign the tank is doing well.

 

[leslie]

I don't mean to doubt your expertise but do sponges really move like a snail? I'm truly a rookie and just want clarification.

 

[mvm]

It's a limpet. Some are reef safe, others are not. Have you noticed any missing corals? If you don't want it, I'll take it.

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[george]

Limpet is correct. I had those in my tank at one time. They didn't survive The Great Hydroid Scrubbing of 2005. They didn't seem to harm my corals, but I also may not have had any they like.

If you observe your tank at night, you'll get a true idea of the population since that's when they come out to feed.

 

[leslie]

OK, that is EXACTLY what it looks like. So I might have more than one? He did roll over a small star polyp colony and they didn't come back out for two days. But other than that, nothing has been harmed. I'm so glad I get to keep him (sorry Matt.)