What is "radiata"

Radiata \Ra`di*a"ta\ (r[=a]"d[i^]*[=a]"t[.a]), n. pl. [NL., fr. radiatus, p. p. See Radiate.] (Zo["o]l.) An extensive artificial group of invertebrates, having all the parts arranged radially around the vertical axis of the body, and the various organs repeated symmetrically in each ray or spheromere.

Note: It includes the c[oe]lenterates and the echinoderms. Formerly, the group was supposed to be a natural one, and was considered one of the grand divisions of the animal kingdom.

Radiata is a taxonomic rank that has been used to classify radially symmetric animals. The term Radiata has united several different groupings of animals, some of which do not form a monophyletic group under current views of animal phylogeny. Because of this and problems of homoplasy associated with using body symmetry as a phylogenetic character, the term is used mostly in a historical context.

In the early 19th century, Georges Cuvier united ctenophores and cnidarians in the Radiata. Thomas Cavalier-Smith, in 1983, redefined Radiata as a subkingdom consisting of Myxozoa, Placozoa, Cnidaria and Ctenophora. Lynn Margulis and K. V. Schwartz later redefined Radiata in their Five Kingdom classification, this time including only Cnidaria and Ctenophora.

Although radial symmetry is usually given as a defining characteristic in animals that have been classified in this group, there are clear exceptions and qualifications. Echinoderms, for example, exhibit unmistaken bilateral symmetry as larvae. Ctenophores exhibit biradial or rotational symmetry, defined by tentacular and pharyngeal axes, on which two anal canals are located in two diametrically opposed quadrants. Some species within the cnidarian class Anthozoa are bilaterally symmetric (For example, Nematostella vectensis). It has been suggested that bilateral symmetry may have evolved before the split between Cnidaria and Bilateria, and that the radially symmetrical cnidarians have secondarily evolved radial symmetry, meaning the bilaterality in cnidarian species like N. vectensis has a primary origin.

Radiata may refer to:

• Radiata, the radially symmetric animals of the Eumetazoa subkingdom
• Radiata Stories, a 2005 action role-playing game for the PlayStation 2
• Corona radiata, in neuroanatomy, a white matter sheet that continues caudally as the internal capsule and rostrally as the centrum semiovale
• Corona radiata (embryology), a structure that surrounds an ovum or unfertilized egg cell, and consist of two or three strata (layers) of follicular cells