What is this THING!
 

I picked up a Toadstool and this "thing" was part of the live rock.
It has a hard curled shell with little barbs on it.
The critter that made the shell resembles a slug/snail, but obviously does not move around much....as it is attached to the live rock. :lol:

It spews out a stringy sticky "net" with the consistency of well..forgive me...mucus. You can see some of this in the photo. At first I thought whatever it was may be dying, but then is began to gobble up the "net" and of course anything within it. Rather disturbing to watch...:shocked!:

Although curious about it, I was thinking of removing it...

Anyone have any idea what this is and is it harmful?

Kind of looks like a type of Sea Hare from that blurry pic

It's a vermitid snail, harmless but the nets they cast out can be kind of annoying

and to help identify other hitchhikers

http://www.xtalworld.com/Aquarium/hitchfaq.htm

http://www.melevsreef.com/id/

Thanks for the reply and the information (links) Marie.

get rid of them before they over populate you tank .
one or two is not a big deal but when your corals all covered in mucus you will not like it.

Yes they can get out of control but they filter feed from food in the water column. If you have excess nutrients floating in the water column you might end up with more to worry about then an explosion of vermitid snails :mrgreen:

I have a few they don't cause any problems for me. Mine only seem to feed when I stir up my sand.

Mind me asking where you bought the toadstool, and the price? I can't seem to find any at a decent price in town.