Nano serpent starfish, Ophioderma cinereum, are small, nano-sized specimens of this common starfish found throughout Folorida and the Caribbean.  They are a very hardy, relatively slow growing starfish that are well suited for any reef tank, and the small size makes them especially suited for a nano or pico reef tank.  They can grow to about 1"" body diameter with arms in the 6"" range, and if you want a larger one go to the starfish section, but these nano ones have a body that's about .25"" in diameter and arms about 2"" long.   Some people and books call these starfish brittle stars, and they are closely related, but we prefer to call all the smooth legged starfish serpent stars, and the spiny-legged stars brittle stars.

 

Serpent and brittle stars are easy to care for in an aquarium and will eat most foods offered to them.  During the day they will generally hide in dark crevices and under things, but will quickly emerge at feeding time and scavenge for stray bits of food that fall to the bottom, so they make a great addition to your clean up crew, ridding your tank of any un eaten food.  They generally get along well with other starfish, and aren't known to eat corals, anemones, zoanthids, or most other sessile invertebrates.  They will eat small clams and flame scallops, so I wouldn't recommend mixing the two.