Zoantharia
Encyclopedia
Zoanthids are an order of cnidaria
Cnidaria
Cnidaria is a phylum containing over 9,000 species of animals found exclusively in aquatic and mostly marine environments. Their distinguishing feature is cnidocytes, specialized cells that they use mainly for capturing prey. Their bodies consist of mesoglea, a non-living jelly-like substance,...

ns commonly found in coral reefs, the deep sea and many other marine environments around the world. These animal
Animal
Animals are a major group of multicellular, eukaryotic organisms of the kingdom Animalia or Metazoa. Their body plan eventually becomes fixed as they develop, although some undergo a process of metamorphosis later on in their life. Most animals are motile, meaning they can move spontaneously and...

s come in a variety of different colonizing formations and in numerous colors. They can be found as individual polyps, attached by a fleshy stolon
Stolon
In biology, stolons are horizontal connections between organisms. They may be part of the organism, or of its skeleton; typically, animal stolons are external skeletons.-In botany:...

 or a mat that can be created from small pieces of sediment
Sediment
Sediment is naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of fluids such as wind, water, or ice, and/or by the force of gravity acting on the particle itself....

, 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.

They are among the most commonly collected coral in aquaria, easily propagating and being very durable in many water conditions.

Nomenclature controversy

The name of the order
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...

 is controversial. Non-specialists often use the term Zoanthidea whereas most taxonomists use Zoantharia. The term Zoantharia in turn is used temporarily instead of Hexacorallia
Hexacorallia
Hexacorallia is a subclass of Anthozoa comprising approximately 4,300 species of water-based organisms formed of colonial polyps generally with 6-fold symmetry. This includes all of the stony corals, which are vital for coral reef formation, as well as all sea anemones, tube anemones, and zoanthids...

. However, major taxonomic papers published since 1899 by specialists (O. Carlgren and F. Pax have described more species than all other authors combined) use Zoantharia, and most recent specialists on the order continue to use the term Zoantharia.

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 (except for the family Zoanthidae). The main characteristic of the order is that their tentacles are organised in two distinct rows.

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
Polymorphism (biology)
Polymorphism in biology occurs when two or more clearly different phenotypes exist in the same population of a species — in other words, the occurrence of more than one form or morph...

 of the same or similar species. Such zooxanthellate genera derive a large portion of their energy requirements from symbiotic dinoflagellate
Dinoflagellate
The dinoflagellates are a large group of flagellate protists. Most are marine plankton, but they are common in fresh water habitats as well. Their populations are distributed depending on temperature, salinity, or depth...

s of the genus Symbiodinium (zooxanthellae), similar to many corals, anemones, and some other marine invertebrates.

Families and genera

The families and genera within the order Zoantharia (also known as Zoanthidea) are :
  • Family Abyssoanthidae
    • Genus Abyssoanthus Reimer & Fujiwara in Reimer, Sinniger, Fujiwara, Hirano & Maruyama, 2007
  • Family Epizoanthidae
    • Genus Epizoanthus Gray, 1867
  • Family Hydrozoanthidae
    • Genus Hydrozoanthus Sinniger, Reimer & Pawlowski, 2010
    • Genus Terrazoanthus Reimer & Fujii, 2010
  • Family Neozoanthidae
    • Genus Neozoanthus
  • Family Parazoanthidae
    • Genus Antipathozoanthus Sinniger, Reimer & Pawlowski, 2010
    • Genus Corallizoanthus Reimer in Reimer Nonaka Sinniger & Iwase, 2008
    • Genus Isozoanthus
      Isozoanthus
      Isozoanthus is a genus of anemone-like anthozoans in the order Zoanthidae-Species:Species in this genus include:* Isozoanthus africanus Carlgren, 1923* Isozoanthus altisulcatus Carlgren, 193* Isozoanthus arborescens...

      Carlgren, 1905
    • Genus Mesozoanthus Sinniger & Haussermann, 2009
    • Genus Parazoanthus
      Parazoanthus
      Parazoanthus is a genus of anemone-like anthozoans in the order Zoanthidae-Species:Species in this genus include:* Parazoanthus anguicomus * Parazoanthus axinellae * Parazoanthus capensis Carlgren, 1938...

      Haddon & Shackleton, 1891
    • Genus Savalia Nardo, 1814 (synonym: Gerardia)
  • Family Sphenopidae
    • Genus Palythoa Lamouroux, 1816
    • Genus Sphenopus
  • Family Zoanthidae
    • Genus Acrozoanthus
    • Genus Isaurus Gray, 1828
    • Genus Zoanthus Cuvier, 1800


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.

Dangers

Some zoanthids contain the highly toxic substance palytoxin
Palytoxin
Palytoxin is a very dangerous toxin; it is considered to be one of the most toxic non-peptide substances known, second only to maitotoxin in terms of toxicity in mice...

. Palytoxin
Palytoxin
Palytoxin is a very dangerous toxin; it is considered to be one of the most toxic non-peptide substances known, second only to maitotoxin in terms of toxicity in mice...

 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
Toxin
A toxin is a poisonous substance produced within living cells or organisms; man-made substances created by artificial processes are thus excluded...

 can be fatal should it be ingested or enter the blood stream. If delivered immediately, vasodilators injected into the ventricle
Ventricle (heart)
In the heart, a ventricle is one of two large chambers that collect and expel blood received from an atrium towards the peripheral beds within the body and lungs. The Atria primes the Pump...

 of the heart can act as an antidote
Antidote
An antidote is a substance which can counteract a form of poisoning. The term ultimately derives from the Greek αντιδιδοναι antididonai, "given against"....

.http://www.cbwinfo.com/Biological/Toxins/Palytoxin.html

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. A 2010 study found toxic zoanthids in three Washington D.C. area aquarium stores.

Palytoxin is a tumor promoter, and is being studied in relation to signaling pathways in skin cancer genesis. Contrary to common belief, palytoxin can be absorbed through intact skin. The danger of acute poisoning from venomous zoanthids is quite real. An aquarist was poisoned through skin injuries on fingers by a Parazoanthus species, but recovered after 3 days. His zoanthid was found to contain 2-3 milligram of palytoxin per gram. For comparison, the intravenous LD50 dose of palytoxin for a grown man is less than 8 microgram. Thus each gram of the offending zoanthid contained enough venom to kill at least 125 grown men.

Diet

Zoanthids feed both by photosynthesis
Photosynthesis
Photosynthesis is a chemical process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can...

, aided by the zooxanthellae they contain, and by capturing plankton
Plankton
Plankton are any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. That is, plankton are defined by their ecological niche rather than phylogenetic or taxonomic classification...

and particulate matter. Although photosynthesis aids in their nutrition, even species that do not actively capture plankton cannot live through photosynthesis alone. Zoanthids can eat meaty foods, such as lancefish, brine shrimp, krill and bloodworms.

External links

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