Harlequin serpent stars, Ophioderma appressum, are very attractive starfish that are suitable for any reef tank, including nano reef tanks. There is quite a bit of color variation in this species, but we try to stick with the ones that look like the one in the picture with white and dark gray-banded legs. The average size we seel have a body that is about the size of an average shirt button, but they can be as large as dime sized. The legs are usually about 2"" to 3"" long, and about the diameter of a cooked spaghetti noodle. If you're looking for a tiny one for a nano tank, just mention it when you order and we'll send a smaller one.
These serpents are real easy to take care of and really require no special care at all. They will usually be hiding under rocks during the day, but as soon as you put food in the water they will come out and actively feel around for food. These starfish will eat anything that gets past your fish, shrimp, and crabs, and they're especially good at finding all those lost food particles that fall behind and under the rocks, so you don't have to worry about stray bits of food fouling the water. They also respond well to directed feeding if you're inclined to do that, but it isn't necessary in most cases.