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 Thanks ScubaSteve,
 #2 doesn't move very often. I'm pretty sure it's just one critter. I've  seen it in a few different places on that rock and it's always sitting  there not doing much.
 
 #3 is tricky to photograph right now. I watched it for a while and the  other side looks like some sort of clam. It's got bilateral symmetry and  pulls itself along with a foot/tongue.
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