Serpent Stars have 5 long slender arms. There are tons of different species, but we sell them as either Red, Orange, Harlequin or common "Serpent" stars. All have the same care and requirements. They tend to be nocturnal, and also active at feeding time. The Reds get larger, and can be 12" in diameter. The Harlequins tend to be the smallest, and even have variations in their color patterns from other Harlequins. The Oranges are slimy on top of the disc, and tend to be the most active of all serpent stars. These are reef safe and good additions to your clean up crews.