Another "what is it" question

K

Kitty

Howdy! I saw this little guy going through my tank a couple of nights ago, and I have found him only at night ever since.

He (?) look like a nasarrius (sp) snail - the same kind of snorkel - but the covering is more like a clam. But it has longish things on it, that look like clove polyps. This critter is small, maybe an inch across.

I touched it with a long pair of tongs, and the covering disappered! The critter became all white ( a shell, I think), and disappeared all together.

I have only seen it on the rocks, never on a coral.

I think it's a cowrie, maybe a "Cypraea miliaris", though the coloring is more brown, and the stalks are slightly different.

I apologize for the pictures, my macro lense is not working properly, besides this guy can MOVE, and is camera shy!

So, do y'all think it is a cowrie? Is is a good thing? I've tried to catch it, but it closes up and gets away.
 
Well a Crowie would have a hard shell. When you say its like a clam, do you mean the shell or the mantle of a clam?

Crowies do have things that stick out like a hedgehog.

In the bottom photo, is it the small round black thing with the gold or yellowish round spot??

Could be a limpet too.
 
The hard shell appears AFTER the mantle, like a clam, goes inside. In the last picture, it is the brown blob :D
I've only seen it one more time, and again, I tried to grab it with a pair of plastic tongs, but it was too slippery, and it got away after the mantle disappeared, and only the shell was showing. (It thought it had spilled it's guts!) But this thing moves much faster than a snail.
 
The pictures are hard to see. It sounds like a cowerie. Their snout is much shorter than a Nasariuss though. Their mantle comes up from beneath to cover their shell (which is why it is so shinny), and usually is pretty bumpy and full of little protrusions. I don't know of any that feed on corals, and it's no surprise that it only comes out at night. The ones I've had love algea, especially film algea on rocks, but they also love to sit on Nori and chew away. If you can get it turned over so that it totally withdraws, the bottom of the shell should have a long "canyon" running full length, sort of zippered if the animal is fully retracted. I'd concider it benficial.

Edit: looking at the picutres again, it looks pretty flatish. A Cowerie's shell is shaped much like a 1/2 a walnut, but smooth.
 
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