It is the star shown in the avatar, which is not reef safe as mentioned in another thread.
this means it will eat corals, zoanthids, anemones, snails, tube worms and anything else it can likely catch or crawl over. So it can not go in a reef, or you can not keep those things with it. A reef, specifically, means corals and such but also includes many other inverts.
You might be able to keep shrimp, crabs or a brittlestar, but it depends on the size of the tank and the parameters. But many other inverts may be eaten. Basically you can consider keep inverts that are able to move, quickly.