Are these critters good

[gon08]

Here they are in a small bucket. As you can see they propel themselves around the tank. There are probably a million of these things in the tank and although they don't seem to hurt anything they ugly up the rock by covering the coraline algae.

http://s1235.photobucket.com/albums/ff426/gonzousa/?action=view&current=2010-11-07_22-04-30_824.mp4