scanning the tank and i seen these flat grey lookin things. at first i just thought they were part of the rock but another look showed that they were moving about the tank. moving from one rock to the other. some kind of shelless snail? flat and grey. good or bad?

Asterina starfish. Generally* good hitchhikers.

Does it look like the grey blob under the central polyp of these palys?


If so, +1 Asterina... they are a mixed lot, some eat corals, others eat algae, and I'm sure others specialize in some other area.

EDIT: For the record, this guy wasn't eating the palys

+++1