Are you refering to a blue linkia (Linckia laevigata). If so, I personaly have never cared for one, but from what ive researched in the past, nobody really knows exactly what they eat some eat some things, and others wont, which is what makes them hard to care for. From what ive read some thrive and others die, and with no ryhme or reason to it
On a side not they are really cool tho