Agreed (though technically Aquilonastra, Asterina is the common hobby name...). These guys often have six arms, but are sometimes seen with five. They don't get a whole lot bigger than the one you've got, but instead rip themselves in half to create clones. For the most part, they feed on coralline algae and detritus, but some have implicated them in the deaths of zoanthids.
Divetoday has a point ... they can multiply to plague proportions. When they do, some folks solve the problem with harlequin shrimp.
~Bruce