Rhizangiidae d'Orbigny 1851

Introduction

The rhizangiids are known from the Lower Cretaceous (about 135 million years ago) to the Recent, and are widespread in the tropical and temperate regions of all oceans. All species live on hard substrates on the continental shelf (0-200 m), but at least one genus (Culicia) is known from as deep as 238 m. All species are azooxanthellate; however, one (Astrangia poculata) contains populations that are also zooxanthellate (Peters et al., 1988). Among the azooxanthellate Scleractinia, the rhizangiids have most successfully occupied the neritic, hard bottom, temperate niche. All Recent rhizangiids are colonial and firmly attached, but because they rarely form large colonies, they do not contribute to shallow or deeper-water reef structure. A total of 33 Recent species is known in four genera (Cairns et al., 1999). This family is sometimes incorrectly referred to as the Astrangiidae Verrill, 1869.

Characteristics

Primarily colonial, azooxanthellate coralla formed by extratentacular budding, resulting in plocoid or reptoid colonies. Corallites usually small and low, united basally by stolons or a thin basal coenosteum. Septa composed of one fan system of simple or compound trabeculae, resulting in finely dentate septal margins. Endotheca present.

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Left: Culicia hoffmeisteri : Calice of an individual corallite from a colonial skeleton collected from Victoria, Australia (depth 7 m). Diameter of corallite 5.5 mm. Photograph from Cairns and Parker, 1992. Copyright © 1995 South Australian Museum. Right: Oulangia bradleyi: Calice of an individual corallite from a colonial skeleton collected at the Galapagos (depth 14 m). Diameter of corallite 12.2 mm (from Cairns, 1991).

Discussion of Phylogenetic Relationships

No phylogenetic analysis has been performed on the genera within this family. The monophyletic nature of the family is doubtful. For instance, Chevalier (1987) included Polycyathus in this family, and Verheij and Best (1987) included both Polycyathus and Paracyathus as rhizangiids, whereas Cairns and Zibrowius (1997) considered both of these genera to be caryophylliids, as well as transferring Colangia and Phyllangia from the Rhizangiidae to the Caryophylliidae. Recent molecular analyses (Romano and Cairns, 2000) place Polycyathus and Paracyathus with the Oculinidae, but as yet no nucleic acids from rhizangiids have been sequenced.

Other Names for Rhizangiidae d'Orbigny 1851

• Astrangiidae

References

Cairns, S. D. 1991. A revision of the ahermatypic Scleractinia of the Galápagos and Cocos Islands. Smithsonian Contributions to Zoology, 504: 32 pp.

Cairns, S. D. 1994. Scleractinia of the temperate North Pacific. Smithsonian Contributions to Zoology, 557: 150 pp.

Cairns, S. D. 1995. The marine fauna of New Zealand: Scleractinia (Cnidaria: Anthozoa). New Zealand Oceanographic Institute Memoirs, 103, 210 pp.

Cairns, S. D., B. W. Hoeksema, and J. van der Land. 1999. Appendix: List of Extant Stony Corals. Attol Research Bulletin, 459:13-46.

Cairns, S. D. and S. A. Parker. 1992. Review of the Recent Scleractinia (Stony Corals) of South Australia, Victoria and Tasmania. Records of the South Australian Museum, Monograph Series, 3: 82 pp.

Cairns, S. D. and H. Zibrowius. 1997. Cnidaria, Anthozoa: Azooxanthellate Scleractinia from the Philippine and Indonesian regions. Mémoires du Muséum National d'Histoire Naturelle, 172: 27-243.

Chevalier, J.-P. 1987. Ordre des Scléractiniares: Systematique. Pp. 679-753 In: Grassé (editor) Traité de Zoologie, 3(3) Masson, Paris.

Peters, E. C. et al. 1988. Nomenclature and biology of Astrangia poculata (Cnidaria: Anthozoa). Proceedings of the Biological Society of Washington, 101(2): 234-250.

Romano, S. L. and S. D. Cairns. 2000. Molecular phylogenetic hypotheses for the evolution of scleractinian corals. Bull. Mar. Sci., 67(3): 1043-1068.

Verheij, E. and M. B. Best. 1987. Notes on the genus Polycyathus Duncan, 1876 and a description of three new scleractinian corals from the Indo-Pacific. Zoologische Mededelingen, 61(12): 147-154.

Wells, J. W. 1956. Scleractinia. Pp. F328-F444 In: Moore, R. C (editor) Treatise on Invertebrate Paleontology, Part F: Coelenterata. University of Kansas Press, Lawrence.