Haven't added anything to the tank in a month (and that was quite a small rock) came in this morning, saw something odd in the water in the corner of the tank, turkey bastered it into viewing position, and discovered...an asterina star!
Asterinas get a bad rap, but most of the FAQs I've read would indicate that it's undeserved--they're scavengers, and many people consider them valueable members of the clean-up crew. Also, they're adorable, not that that's influencing me in any way.
Mine was still alive, as indicated by wee little tube feet extending, and promptly vanished into the rock, so I probably couldn't remove him even if I wanted to. Godspeed, little starfish!