Can't ID this little thing..

I just started my first tank almost 2 weeks ago. I've got 3 feather duster worms (that are growing noticeably every day!), a couple stomatella snails, and this just showed up last night. It's very small, only a couple millimeters wide. It moves around very slow. Kind of a blue-ish gray center, and white on the edges. I know the pictures are garbage, but hopefully they're OK enough to ID!