Hexacorallia is a

class Class, Classes, 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 d ...

Anthozoa Anthozoa is one of the three subphyla of Cnidaria, along with Medusozoa and Endocnidozoa. It includes Sessility (motility), sessile marine invertebrates and invertebrates of brackish water, such as sea anemones, Scleractinia, stony corals, soft c ...

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 colonial marine invertebrates within the subphylum Anthozoa of the phylum Cnidaria. They typically form compact Colony (biology), colonies of many identical individual polyp (zoology), polyps. Coral species include the important Coral ...

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 constituting the order (biology), order Actiniaria. Because of their colourful appearance, they are named after the ''Anemone'', a terrestrial flowering plant. Sea anemone ...

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: * A socio-political or established or existing order, e.g. World order, Ancien Regime, Pax Britannica * Categorization, the process in which ideas and objects are recognized, differentiated, and understood ...

s. The hexacorallia are distinguished from another class of Anthozoa,

Octocorallia Octocorallia, along with Hexacorallia, is one of the two extant classes of Anthozoa. It comprises over 3,000 species of marine and brackish animals consisting of colonial polyps with 8-fold symmetry, commonly referred informally as "soft cora ...

, 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 invertebrates found both in fresh water, freshwater and marine environments (predominantly the latter), including jellyfish, hydroid (zoology), hydroids, ...

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

plankton Plankton are the diverse collection of organisms that drift in Hydrosphere, water (or atmosphere, air) but are unable to actively propel themselves against ocean current, currents (or wind). The individual organisms constituting plankton are ca ...

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 coral The Rugosa or rugose corals are an extinct class of solitary and colonial corals that were abundant in Middle Ordovician to Late Permian seas. Solitary rugosans (e.g., '' Caninia'', '' Lophophyllidium'', '' Neozaphrentis'', '' Streptelasma ...

Phylogeny

Hexacorallia is considered to be

monophyletic In biological cladistics for the classification of organisms, monophyly is the condition of a taxonomic grouping being a clade – that is, a grouping of organisms which meets these criteria: # the grouping contains its own most recent co ...

, 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 Ceriantipatharia is a deprecated order of corals within the class Hexacorallia, although it was initially considered as a subclass in older taxonomies. It was split and it is now replaced by its previous two constituent orders, Ceriantharia ( ...

, though more recent genetic studies place it in Hexacorallia. The class 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 constituting the order Actiniaria. Because of their colourful appearance, they are named after the '' Anemone'', a terrestrial flowering plant. Sea anemones are classified in the phy ...

– sea anemones *

Antipatharia Antipatharians, also known as black corals or thorn corals, are an order of soft deep-water corals. These corals can be recognized by their jet-black or dark brown chitin skeletons, which are surrounded by their colored polyps (part of coral th ...

– 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, wi ...

– corallimorpharians aka "false corals" * †

Rugosa The Rugosa or rugose corals are an extinct Class (biology), class of solitary and Colony (biology), colonial corals that were abundant in Middle Ordovician to Late Permian seas. Solitary rugosans (e.g., ''Caninia (genus), Caninia'', ''Lopho ...

– 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 polyps and have a cylindrical body crowned by an oral disc in which a mo ...

– stony corals * †

Tabulata Tabulata, commonly known as tabulate corals, is a class of extinct corals. They are almost always colonial, forming colonies of individual hexagonal cells known as corallites defined by a skeleton of calcite, similar in appearance to a honeycomb. ...

– 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