I have a tiger serpent sea star, it's dark brown with tan stripes going down its arms. It doesn't burrow, but its is nocturnal so it spends the day time underneath my live rock. Serpents are reef state, stay relatively small (arm to arm won't go much over 1', but the body doesn't get big at all), and eat all sorts of detritus. He gets pretty active when I feed, as he'll crawl out in order to grab food. Probably my favorite invertebrate.
They aren't really tough to care for, just realize it's not something you'll see all the time.