My guess is palythoa also. Zoanthus are usually smaller and more tightly packed. One good indicter, but not a 100%, is to try spot feeding. Though all Zoanthids feed Zoanthus do not take foods by closing around it and palythoas do, but not all palythoas will, at least not all the time. But in any case, usually a slit for mouth indicates a palythoa or protopalythoa and a protopalythoa slimes when irritated/touched or removed from the water. Both palythoa and protopalythoa can have sand grains imbedded in thier tissue which is another way to tell the difference between palys and zoanthus.
