Difference Between Palys & Zoas

The zooanthids are small and colorful soft corals that include zoanthus (zoa) and palythoa (paly) polyps . Despite obvious similarities between the two polyp types, there are a number of significant differences as well. Palythoa, or button polyps, comprise growths of polyps which resemble tiny sea anemones, although they are more closely related to corals than to anemones. Zoanthus, like palythoa polyps, are joined along their base and form a continual mat, but this base is not as thick as in the case of palythoa. The tentacles of zoanthus polyps are longer than those of the palythoa polyps. Select palythoa species are toxic, including Palythoa toxica and Palythoa tuberculosa.

  1. Coenenchyme

    • Zoanthus polyps, or sea mats, which are in the group of zoanthids, are colonies of relatively small polyps that are normally less than 1/2 inch in diameter. These polyps grow as encrusting mats from which the short polyps emerge. The thick matlike tissue which joins them is termed the coenenchyme. Palythoa polyps form a thicker base than the zoanthus polyps. This encrusting, clumplike coenenchyme is easily visible, as the individual polyps do not stick up as much as in the zoanthus types. Sea sand and shell fragments are also caught in this bases, which is not the case with the zoanthus type organism.

    Tentacles and color

    • Each individual zoanthus polyp within the colony has a number of blunt tentacles which are longer than those in a palythoa colony, which resemble a ring of bumps rather than genuine tentacles. Zoanthus polyps tend to be more vividly colored than the palythoa colonies and may be a vivid red or orange. Zoanthus polyps are also found in blue and green, while those of palythoa, are more commonly a mixture of brown and cream.

    Plankton Feeders

    • Zoanthus polyps, which encrust over most coral reef surfaces and occasionally grow over other coral species, are filter-feeding animals and don't eat large prey. Palythoa colonies will capture and feed on copepods and other tiny marine creatures. Under captive conditions, the aquarists can offer a palythoa colony thin strips of recently thawed or fresh prawn, fish flesh or mussel meat.

    Currents and Toxins

    • Zoanthus colonies in the marine aquarium require fairly strong currents to bring their plankton diet to them. Palythoa colonies are less dependent on a strong current, as they will capture tiny marine creatures which crawl over their polyps. Palythoa polyps produce a more deadly toxin than zoanthus colonies. This toxin, termed palytoxin, is located in the mucus that covers the polyps and they should only be handled with gloves.