Zoantharia


Zoanthids are an order of hexacorals.
Zoanthids are 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 different 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.
These are among the most commonly collected corals in reef aquaria, easily propagating and very durable in many water conditions.

Other use of the name Zoantharia

The name Zoantharia is often used as a synonym of Hexacorallia, i. e. in a much broader sense than in this article.

Characteristics

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. A main characteristic of the order is that their tentacles are all marginal. Most species propagate asexually and the offspring of the original polyp remain connected to each other, by a stolonal network or coenosarc. Some species are solitary.
While the most well-known zoanthids are the zooxanthellate genera found in tropical and sub-tropical waters, many other species and genera exist, some still relatively unknown to science. Many zoanthids 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 dinoflagellates of the genus Symbiodinium, similar to many corals, anemones, and some other marine invertebrates.

Families and genera

The families and genera within the order Zoanthinaria/Zoantharia/Zoanthidea are:
Suborder Macrocnemina
Suborder Brachycnemina
Note: there are some zoanthid genera such as Neozoanthus or Paleaozoanthus for which there are currently only few data available, those zoanthids having never been found again since their original description.

Aquaria

Zoanthidae include many species popular in the fishkeeping world, among hobbyists and professionals. They are relatively easy to keep alive and healthy, and will often spread to cover rocks in their bright circles of color. They are known by some as carpet coral, button polyps, and "zoas" or "zoos."

Captive propagation

Zooanthids and Palythoa are propagated in captivity by cutting the polyps apart using a scalpel or scissors then attaching to a surface with cyanoacrylate glue. Gloves and goggles should be worn during this process. Drying the polyps with paper towel then gluing them to a small base with gelled cyanoacrylate glue ensures they do not drift in the aquarium when reintroduced.

Toxicity

Some members of this order contain the highly toxic substance palytoxin. Even in small quantities, palytoxin can be incapacitating or potentially fatal. A 2010 study found toxic species for sale in three Washington, D.C. area aquarium stores.
Reports are varied and conflicting on the potential dangers of handling the animal in the aquarist hobby. General opinion and practical experience holds that in order for this toxin to be dangerous to humans, the average aquarist would need to expose mucous membranes or freshly lacerated skin to the polyps, and average handling, propagation and aquarium maintenance is unlikely to pose any danger beyond a localized skin reaction.
Other sources state that palytoxin can be absorbed through intact skin, and the danger of acute poisonings is quite real. According to a published case report a hobbyist was poisoned through skin injuries on fingers by a species of Parazoanthus, but recovered after three days. His zoanthid was found to contain 2-3 milligrams of PTX per gram.
Research suggests that in sublethal quantities, palytoxin is a tumor promoter.
Generally speaking, it is considered proper practice to always wear appropriate protective gloves and goggles when handling sea invertebrates.

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. Zoanthids are often fed brine shrimp or krill when kept in aquariums.