Hexacorallia is a

class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used differentl ...

Anthozoa Anthozoa is a subphylum of marine invertebrates which includes the sea anemones, Scleractinia, stony corals and Alcyonacea, soft corals. Adult anthozoans are almost all attached to the seabed, while their larvae can disperse as part of the plank ...

comprising approximately 4,300 species of aquatic organisms formed of polyps, generally with 6-fold symmetry. It includes all of the stony

coral Corals are marine invertebrates within the class Anthozoa of the phylum Cnidaria. They typically form compact colonies of many identical individual polyps. Coral species include the important reef builders that inhabit tropical oceans and sec ...

s, most of which are colonial and reef-forming, as well as all

sea anemone Sea anemones are a group of predation, predatory marine invertebrates of the order (biology), order Actiniaria. Because of their colourful appearance, they are named after the ''Anemone'', a terrestrial flowering plant. Sea anemones are classifi ...

s, and

zoanthids Zoanthids ( order Zoantharia also called Zoanthidea or Zoanthiniaria) 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 coloniz ...

, arranged within five extant

order Order, ORDER or Orders may refer to: * Categorization, the process in which ideas and objects are recognized, differentiated, and understood * Heterarchy, a system of organization wherein the elements have the potential to be ranked a number of d ...

s. The hexacorallia are distinguished from another class of Anthozoa, Octocorallia, in having six or fewer axes of symmetry in their body structure; the tentacles are simple and unbranched and normally number more than eight. These organisms are formed of individual soft polyps which in some species live in colonies and can secrete a

calcite Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...

skeleton. As with all

Cnidaria Cnidaria () is a phylum under kingdom Animalia containing over 11,000 species of aquatic animals found both in freshwater and marine environments, predominantly the latter. Their distinguishing feature is cnidocytes, specialized cells that th ...

ns, these organisms have a complex life cycle including a motile

plankton Plankton are the diverse collection of organisms found in Hydrosphere, water (or atmosphere, air) that are unable to propel themselves against a Ocean current, current (or wind). The individual organisms constituting plankton are called plankt ...

ic phase and a later characteristic

sessile Sessility, or sessile, may refer to: * Sessility (motility), organisms which are not able to move about * Sessility (botany), flowers or leaves that grow directly from the stem or peduncle of a plant * Sessility (medicine), tumors and polyps that ...

phase. Hexacorallia also include the significant extinct order of rugose corals.

Phylogeny

Hexacorallia is considered to be

monophyletic In cladistics for a group of organisms, monophyly is the condition of being a clade—that is, a group of taxa composed only of a common ancestor (or more precisely an ancestral population) and all of its lineal descendants. Monophyletic gro ...

, that is all contained species are descended from a common ancestor, however it has been suggested that many of the current orders are not. Historically, Antipatharia was considered to be in a separate class called Ceriantipatharia, though more recent genetic studies place it in Hexacorallia. The subclass includes important coral reef builders such as the stony corals, sea anemones, and zoanthids. The recognized orders are shown below: *

Actiniaria Sea anemones are a group of predatory marine invertebrates of the order Actiniaria. Because of their colourful appearance, they are named after the ''Anemone'', a terrestrial flowering plant. Sea anemones are classified in the phylum Cnidaria, ...

- sea anemones * Antipatharia - black corals *

Corallimorpharia Corallimorpharia is an order of marine cnidarians closely related to stony or reef building corals (Scleractinia). They occur in both temperate and tropical climates, although they are mostly tropical. Temperate forms tend to be very robust, wit ...

- corallimorpharians aka "false corals" * † Rugosa - rugose corals *

Scleractinia Scleractinia, also called stony corals or hard corals, are marine animals in the phylum Cnidaria that build themselves a hard skeleton. The individual animals are known as polyp (zoology), polyps and have a cylindrical body crowned by an oral di ...

- stony corals * † Tabulata - tabular corals *

Zoantharia Zoanthids ( order Zoantharia also called Zoanthidea or Zoanthiniaria) 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 coloniz ...

- zoanthids

References

External links

* {{Taxonbar, from=Q132674 Anthozoa Animal classes