Marine Bio Question about echinoderms!?

A new class of echinoderms, the sea daisies or concentricycloids, was discovered in 1986. They are deep water animals living on sunken wood. They are flat and round, looking very much like a small sea star without arms. They also lack a gut. Without ever having seen them, why do you think they are classified as echinoderms, not as a member of a new phylum? Any hypotheses as to how they feed or move around?