As a general rule, if it has big knobs on it (eg chocolate chip, red african, etc), it is not reef safe. (The one EmilyB showed is a bit different, and should be OK).
Sand sifter stars will eat many things in a deep sand bed, and are not good for such a system.
Linkia stars, including the blue and "orange" are typically reef safe. They eat bacterial/algal films and need a mature tank with lots of live rock.
Fromia stars also fall into this group.
Brittlestars are generally considered safe, though some care should be taken with the green brittlestar as it has been known (in tanks and in the wild) to take small fish, shrimp and snails. Other brittles do not appear to have this, um, habit.
Regardless of which seastar or brittlestar you choose, acclimation is key. Be sure to do a loooooong, sloooooooow, drip acclimation, on the order of many hours. This is
especially important with the
Linkia stars.
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The Ophiuroidea: Your guide to the 'stars!
(Brittlestars that is...)
http://home.att.net/~ophiuroid
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[ April 19, 2002: Message edited by: ophiuroid ]
[ April 19, 2002: Message edited by: ophiuroid ]</p>