I have hundreds of them, from my FL live rock. I love them, but mine stay very small. Some of them ride on the backs of my snails, lol, going for a ride. When you feed or stir up the substrate, you'll see them come out and catch debris to feed. At first I thought I got some dog hair in the tank, but it was the vermatid snail. They help keep the water column clean. Not everybody's cup of tea, but mine seem to behave! :D