May need Help - starfish outbreak ???

[maron6977]

Tank & rock I got used about 6 months ago . I noticed a couple months ago , looked like a couple small sand sifting starfish . Over the last month I've noticed more & more . They are all approx. 8-10mm & seem to start out 2 or 3 legs & body then develop into 6 legs . I think I can easily see @ least a dozen now & probably more .
From my experience anything that multiples like that can be a problem !!!
But I've never seen or heard of this .
Anybody have input would be appreciated .