Anthozoa

From Palaeos

o Radiata (grade)
|?--Ctenophora
`--+--Cnidaria  
   |  |--Anthozoa
   |  `--+--Hydrozoa
   |     `--+--+--Scyphozoa
   |        |  `--Cubozoa
   |        `?-Conulata (polyphyletic?)
   `--Bilateria

A Middle Devonian (Eifelian) coral reef, featuring the crinoid Dolatocrinus, the tabulate coral Favosites (with a trilobite) (lower right corner), and a number of species of Rugose corals. The giant one in the center would be Siphonophrentis gigantea, the squat white ones at the middle right are Heterophrentis prolifica, and the cluster of yellow ones in the middle foreground and right middle background are colonial corals of the genus Eridophyllum.

[edit] Introduction

Anthozoans include corals, sea anemones, sea pens, and related organisms. These animals are either solitary or colonial polyps that live attached to a substrate (surface). This is the largest and ecologically the most important group of cnidarians.

Barbouria sp., Lower Pennsylvanian coral from the Ely Formation, Millard County, Utah

Anthozoans are unique in their absence of a medusoid phase. Instead, they release sperm and eggs that form a planula, which attaches to some substrate on which the cnidarian grows. Some anthozoans can also reproduce asexually through budding. Many, especially coral, reproduce both asexually and sexually.

The polyps are much larger than are found in the other two classes. The polyp shows biradial symmetry, with the body cavity divided by septa.

Some species also harbour dinoflagellates called zooxanthellae, in a symbiotic relationship; the reef building corals known as hermatypic corals rely on this symbiotic relationship particularly. The zooxanthellae benefit by using nitrogenous waste and carbon dioxide produced by the host, and the cnidarian gains photosynthetic capability and increased calcium carbonate production in hermatypic corals.

There are 6,000 known recent species, and many additional fossil types.

o Cnidaria  
`--o Anthozoa
   |--Octocorallia (Alcyonaria)
   `--o Hexacorallia (Zoantharia)
      `--+-- Ceriantharia
         `--+-- Tabulaconida
            `--+-- Cothoniida
               `--+-- Tabulata
                  `--+-- Heliolitida
                     `--+--+-- Rugosa
                        |  `-- Heterocorallia
                        |--Actiniaria
                        `--+--Zoanthidea
                           `--+--Antipatharia
                              |?-Kilbuchophyllida
                              `--+-- Corallimorpharia
                                 `--+-- Numidiaphyllida
                                    `-- Scleractinia 

[edit] Information

Author: Ehrenberg, 1831

Stratigraphic range: Cambrian to Recent

Distribution: Cosmopolitan Marine

Lifestyle: Sessile Epifaunal microcarnivore or carnivore

Evolutionary biota in which of importance: Paleozoic, Mesozoic-Cenozoic

[edit] Classification and Phylogeny

As with the Cnidaria in general (and for that matter many other taxa), precise relationships between different anthozoan taxa are the subject of much debate.

Most anthozoan classificatrions and phylogenies are based on the primary dichotomy of the Octocorallia and the Hexacorallia, or the Alcyonaria and Zoantharia (the names amount to the same thing). These are the two main groups, classified according to fundamental symmetry (eightfold vs. sixfold, obviously). In view of the fact that symmetry can vary greatly between groups of organisms - e.g. the radially symmetrical echinoderms are included with the chordates (vertebrates, etc.) in the Deuterostomia, one wonders how wise this approach is. One alternative classification has a distinct subclass Ceriantipatharia consisting of the orders Antipatharia and Ceriantharia which share a number of similarities. There is also the question of extinct taxa. Sometimes the Tabulate corals are considered a distinct subclass (there was even the suggestion that maybe they weren't animals at all, but a type of algae) [need to fine reference]. The rugose corals have also been given their own subclass, the Rugosa or Tetracorallia. More commonly nowadays all these groups are considered orders of the Hexacorallia.

The following tree, based on Fautin, Romano, and Oliver 2000. Zoantharia. Sea Anemones and Corals (Tree of Life Web Project, (tree derived from Oliver 1996, France et al. 1996, and Chen et al. 1995) is from Mikko's Phylogeny Archive and represents one possible phylogeny, although emphasising the Hexacorallia or Zoantharia only.

<==o ANTHOZOA 
   |-- Octocorallia
   `--o Hexacorallia
      |--+-- †Kilbuchophyllida
      |  `--+?-o Ceriantharia
      |     `--+--o Corallimorpharia
      |        |--+?- Ptychodactiidae [Ptychodactiatria]
      |        |  `-- Actiniaria
      |        `--+-- Numidiaphyllida
      |           `-- Scleractinia [Madreporaria]
      `--+-- Tabulaconida
         `--+-- Cothoniida
            `--+-- Tabulata
               `--+-- Heliolitida
                  `--+--+?- Heterocorallia
                     |  `-- Rugosa
                     `--+?- Antipatharia
                        `-- Zoanthidea

© Mikko Haaramo

However the recent molecular and morphological-based phylogeny of Daly et al. (2003), which involves living taxa only, represents hexacoral relationships as follows:

o Root
|--Ceriantharia
`--o Hexacorallia
   |--Actiniaria
   `--+--Zoanthidea
      `--+--Antipatharia
         `--+--Corallimorpharia
            `--Scleractinia

See also Cnidaria phylogeny for an alternative arrangement

[edit] References

• Conway Morris, S., 1993: The fossil record and early evolution of the Metazoa. --Nature, vol. 361, 21 January, pp. 219-225
• Daly, M, DG Fautin & VA Cappola (2003), Systematics of the Hexacorallia (Cnidaria: Anthozoa). Zool. J. Linn. Soc. 139: 419–437.
• Fautin, D. G., Romano, S. L. & Oliver, W. A. Jr., 1999: Zoantharia - Sea Anemones and corals. The Tree of Life
• Parker, S. P. (ed.), 1982: Synopsis and classification of living organisms. Vols. 1 & 2 --McGrew-Hill Book Company

[edit] Links

• Introduction to the Anthozoa at UCMP
• Tree of Life - Anthozoa

[edit] Credits

Kheper MAK990603; Palaeos com MAK020616; Palaeos org MAK061029; (with some content from Wikipedia)