The Zoantharia are an order of the Anthozoa with about 300 known species. They are also known under the names Zoanthidea or Zoanthinaria. This can lead to confusion because there is also a family called Zoanthidae.
A key feature of the Zoantharia is the missing lime skeleton. To support their structure, they absorb sand and other materials into their tissues. This is done by means of a separate, sticky mucus. The whole is then surrounded by an outer skin and forms a stable skeleton.
Another feature of the order is that their tentacles are clearly arranged in two rows.
Distribution and Habitat
Zoantharia live predominantly in tropical and subtropical seas. Parazoanthus axinellae is, for example, an exception, which also occurs in the Mediterranean.
They colonize both organic and inorganic material. For example, some species use sponges and other corals as “basic building blocks”. Also snails, crustaceans and tunicate can be a place of residence.
Many species live near the coast, but some are also deeper. Zoantharia have so far been little explored. There is still a need for research in all areas, including the depth in which they live.
Many species of Zoantharia live in colonies and thus form a crust. This can be done on rocks, sponges, corals or other animals. Some species also live solitaire.
Some of them are particle feeders, while others live in symbiosis with algae. The latter often have a brown or green colour due their symbiosis.
Types of Zoantharia from the genus Palythoa have one of the strongest natural poisons. This species also includes the two species Palythoa canariensis and Palythoa caribaeorum occurring in the Canary Islands. The poison is probably not produced by the animal itself, but by symbiotic bacteria.
Epizoanthus incrustatus lives on houses of hermit crabs. In doing so, it solves this completely, and the hermit crab lives exclusively in the crust of the anemone.
Isozoanthus giganteus is the largest species of Zoantharia with a length of 19 cm and a diameter of 2 cm.