something from the family Zonthidae.
If the polyps are embedded in (or arise from) a common mat, it would be of the genus Palythoa.
If the polyps are separate, but crowded together, it would be in the genus Zoanthus or Protopalythoa. Typically, Zoanthus are smaller polyps around 1/2" or so, and the Protopalythoa are larger. Protopalythoa also (usually) have a rough surface because they incorporate sediments in to their tissues.