What are these little creatures?

This morning while looking at my saltwater tank I noticed these weird little things! They look like tiny, tiny starfish but some only have 4 "leg" bumps and others look like they're trying to have 5. They are only a few millimeters and are grey. The problem is I haven't had a starfish in over a year and he had major problems. All of my rock started as dry, plain dead rock with the exception of maybe 2 small pieces of live. This is the first time I've seen them in 2+ years. They are definitely moving all over the glass. Just curious what these guys are. I will try to attach pictures.