#pest ? critterid

Can someone help identify what this is? There is quite a few of them in one corner of the tank but this one was easier to get a picture of.

Need help anybody know what this is?

Hello, Yesterday I noticed these things, marked up in the image, in my tank. I tried poking them and they close up and retreat to the hole in the live rock. Can someone identify them? and tell me whether I need to do something about them? N.B. I always dip my corals in Seachum dip, and I don't...

Anyone know what these are and if I should/ how, get rid of them?? I do a 25% water change about every 10 days but doesn’t effect them at all