brittle stars are usually very hardy but if you didnt drip acclimate them then they go through osmotic shock and it can kill them brittle stars sometimes can come back from this but most others have no chance a pic would help to figure out if this is the case or not.
Mike
salinity or specific gravity it should be at 1.025-.026 for inverts. if the water it was shipped was lower a big jump will cause this try to feed it pieces of shrimp or other meaty food and see if it will take it.
mike