Zoanthid

Zoanthids (order Zoantharia) are an order of cnidarians commonly found in coral reefs, the deep sea, and many other marine environments around the world. These animals come in a variety of different colonizing formations and in numerous colors. They can be found as individual polyps, attached by a fleshy stolon or a mat that can be created from small pieces of sediment, sand and rock. The term "zoanthid" refers to all animals within this order Zoantharia, and should not be confused with "Zoanthus", which is one genus within Zoantharia.

Zoanthids can be distinguished from other colonial anthozoans and soft coral by their characteristic of incorporating sand and other small pieces of material into their tissue to help make their structure. All known zoanthids have this unique feature, excepting the Family Zoanthidae. While the most well-known zoanthids are the zooxanthellate genera found in tropical and sub-tropical waters (primarily Zoanthus and Palythoa), many other species and genera exist, some still relatively unknown to science. Many zoanthids (in particular the genera Epizoanthus and Parazoanthus) are often found growing on other marine invertebrates.

Often in zooxanthellate genera such as Zoanthus and Palythoa there are a large number of different morphs of the same or similar species. Such zooxanthellate genera derive a large portion of their energy requirements from symbiotic dinoflagallates of the genus Symbiodinium (zooxanthellae), similar to many corals, anemones, and some other marine invertebrates.

Zoanthids (e.g., Montlivaltia) are known in the fossil record from the Triassic period onwards. Many familiar forms such as the Madrepores have survived essentially unchanged for many millions of years.

List of families and genera within the order Zoantharia (also known as Zoanthidea):
 * Family Abyssoanthidae
 * Genus Abyssoanthus
 * Family Epizoanthidae
 * Genus Epizoanthus
 * Family Parazoanthidae
 * Genus Parazoanthus
 * Genus Isozoanthus
 * Genus Savalia
 * Family Sphenopidae
 * Genus Palythoa
 * Genus Sphenopus
 * Family Zoanthidae
 * Genus Zoanthus
 * Genus Acrozoanthus
 * Genus Isaurus

Additionally, there are other zoanthid genera such as Neozoanthus for which there are currently only few data available.

Dangers
Some zoanthids contain the highly toxic substance palytoxin. Palytoxin is one of the most toxic organic substances in the world, but there is an ongoing debate over the concentration of this toxin in these animals. However, even in small quantities, the toxin can be fatal should it be ingested or enter the blood stream. If delivered immediately, vasodilators injected into the ventricle of the heart can act as an antidote.

In order for this toxin to be dangerous to humans, the average aquarist would need to ingest the zoanthid in sufficient quantities, or brush a recent cut over it. Average handling, propagation and aquarium maintenance is unlikely to pose any danger beyond a localized skin reaction.

Diet
Zoanthids feed both by photosynthesis, aided by the zooxanthellae they contain, and by capturing plankton and particulate matter. Although photosynthesis aids in their nutrition, even species that do not actively capture plankton cannot live through photosynthesis alone. Zoanthis can eat meaty foods, such as lancefish, brine shrimp, krill and bloodworms.