here is a quote from Eric borneman
"Palythoa species are recognized by having a coenenchyme that contains bits of debris and reef elements that help to support the polyp. The colonies may form large tracts of individual colonies that often grow in a curved convex shape and usually remain less than a foot across. They have polyps with wide flattened oral disks and variously shaped tentacles surrounding the outer margin of the oral disk. Their colors are typically more muted shades of brown with some fluorescent elements to the tentacles and oral disks common. They may also have a marbled or striated pattern on the oral disk. Palythoa are normally voracious feeders, accepting food willingly. The overall need for feeding is somewhat questionable, although most zoanthids do not produce enough energy from photosynthesis to meet their daily needs. They reproduce by budding from their stolons, remaining attached and connected by the coenenchyme.
Protopalythoa is different from Palythoa in that the polyps are not immersed in the coenenchyme. They are undoubtedly closely packed together, but they remain individual. These animals can form small or even solitary colonies, though they are far more commonly found in huge landscapes that encrust the reef substrate. Their polyps are most frequently brown, with usually shorter and blunted tentacles surrounding the oral disk. The tentacles and oral disk (often marbled of striated) are often of contrasting color to the polyp body. These species have prolific mesenteries, often numbering more than sixty.
Zoanthus are normally much smaller polyps and they do not incorporate sediment into their bases. A divided sphincter muscle is the heretofore base of their classification. They reproduce by budding from the base of the parent colony to form very large mats of stoloniferous polyps which encrust the reef substrate. They are not normally seen to feed on large prey. Zoanthus are normally brightly colored animals, usually with oral disks 1/2" or less across their diameter.
