What kind of starfish is this?

[Huntersreef]

I’ve been watching this little guy for a couple months. Came in on a coral frag. He does not get near the coral and just cleans the rocks. He is a blueish grey.

 

[sbeason]

Looks like an Asterina star to me.

 

[Jekyl]

+1 asterina. In no time you'll have hundreds lol.

 

[Mark Goode]

I think it's the first time I've actually seen a whole one - three arms is usual. I only see them at night though, so not currently a problem.