unidentified hitchhicker

[lineman]

Weve got some type of mollusk(?) that was attached to the rock our mushroom came on, and now its out in the middle of the tank, blowing what looks like smoke out in little puffs. It's gray about an inch long, 3/8 inch wide, a half shell, moves pretty fast. Will try to post a picture next time he appears, in the mean time, any ideas what he is? Is he dangerous for the tank?

[ravenmore]

I believe most mollusks are filter feeders and aren't harmfull. My guess on the blowing smoke would be a reproductive act such as sending sperm/eggs into the water column.

[Biomanjcs72]

If the half shell resembles half of a clam or scallop shell, then I'd say it's probably a Limpet of somekind (really hard to tell without a pic). Probably not harmful. I haven't heard of any evil limpets, but then again, I don't exactly spend a lot of time studying limpets either. HTH