radiata

{{Short description|Taxonomic rank that has been used to classify radially symmetric animals}}

{{Other uses}}

{{Taxobox

| name = Radiata

| fossil_range = Ediacaran – Present {{fossilrange|610|0|}}

| image = Jean Louis Agassiz 1870.jpg

| image_caption = Louis Agassiz in 1870, with drawings of animals then considered Radiates

| regnum = Animalia

| subregnum = Eumetazoa

| unranked_superphylum = Radiata

| subdivision_ranks = Phyla

}}

Radiata or Radiates is a historical taxonomic rank that was used to classify animals with radially symmetric body plans. The term Radiata is no longer accepted, as it united several different groupings of animals that do not form a monophyletic group under current views of animal phylogeny. The similarities once offered in justification of the taxon, such as radial symmetry, are now taken to be the result of either incorrect evaluations by early researchers or convergent evolution, rather than an indication of a common ancestor. Because of this, the term is used mostly in a historical context.{{cite book |last=Hadzi |first=J. |title=The Evolution of the Metazoa |url=https://archive.org/details/evolutionofmetaz00hadz |year=1963 |publisher=The Macmillan Company |location=New York, NY, USA|isbn=0080100791 |pages=[https://archive.org/details/evolutionofmetaz00hadz/page/56 56–57]}}

In the early 19th century, Georges Cuvier united Ctenophora and Cnidaria in the Radiata (Zoophytes).{{cite book|last=Cuvier |first=Georges |author-link=Georges Cuvier |title=Le Règne Animal Distribué Selon son Organisation, pour Servir de Base à l'Histoire Naturelle des Animaux et d'Introduction à l'Anatomie Comparée |year=1817 |publisher=Déterville |location=Paris}} Thomas Cavalier-Smith, in 1983, redefined Radiata as a subkingdom consisting of Myxozoa, Placozoa, Cnidaria and Ctenophora.{{cite book |last=Cavalier-Smith |first=Thomas |author-link=Thomas Cavalier-Smith |title=A 6-kingdom classification and a unified phylogeny. in Endocytobiology II |year=1983 |publisher=Walter De Gruyter |isbn=3110086603 |pages=1027–1034}} Lynn Margulis and K. V. Schwartz later redefined Radiata in their Five Kingdom classification, this time including only Cnidaria and Ctenophora.{{cite book |last=Margulis |first=Lynn |author-link=Lynn Margulis |title=Five Kingdoms: An illustrated Guide to the Phyla of Life on Earth |year=1988 |publisher=W. H. Freeman |location=New York |isbn=0716730278 |url-access=registration |url=https://archive.org/details/fivekingdomsillu00marg_0 }} This definition is similar to the historical descriptor Coelenterata, which has also been proposed as a group encompassing Cnidaria and Ctenophora.{{cite journal |last1=Philippe |first1=Hervé |last2=Derelle |first2=Romain |last3=Lopez |first3=Philippe |last4=Pick |first4=Kerstin |last5=Borchiellini |first5=Carole |last6=Boury-Esnault |first6=Nicole |last7=Vacelet |first7=Jean|last8=Renard |first8=Emmanuelle |last9=Houliston |first9=Evelyn |last10=Quéinnec |first10=Eric |last11=Da Silva|first11=Corinne |last12=Wincker |first12=Patrick |last13=Le Guyader |first13=Hervé |last14=Leys |first14=Sally |last15=Jackson |first15=Daniel J.|last16=Schreiber |first16=Fabian |last17=Erpenbeck |first17=Dirk |last18=Morgenstern |first18=Burkhard |last19=Wörheide |first19=Gert |last20=Manuel |first20=Michaël |title=Phylogenomics Revives Traditional Views on Deep Animal Relationships |journal=Current Biology |date=April 2009|volume=19 |issue=8 |pages=706–712|doi=10.1016/j.cub.2009.02.052 |pmid=19345102|s2cid=15282843 |doi-access=free |bibcode=2009CBio...19..706P }}{{cite journal |last1=Dunn |first1=Casey W. |last2=Leys |first2=Sally P. |last3=Haddock |first3=Steven H.D. |author3-link=Steven Haddock |title=The hidden biology of sponges and ctenophores |journal=Trends in Ecology & Evolution |date=May 2015 |volume=30 |issue=5 |pages=282–291 |doi=10.1016/j.tree.2015.03.003|pmid=25840473 |doi-access=free |bibcode=2015TEcoE..30..282D }}

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 unmistakable bilateral symmetry as larvae, and are now in the Bilateria. Ctenophores exhibit biradial or rotational symmetry, defined by tentacular and pharyngeal axes, on which two anal canals are located in two diametrically opposed quadrants.{{cite journal |last=Martindale |first=Mark |author2=Finnerty, J.R. |author3=Henry, J.Q. |title=The Radiata and the evolutionary origins of the bilaterian body plan|journal=Molecular Phylogenetics and Evolution |date=September 2002 |volume=24 |issue=3 |pages=358–365 |doi=10.1016/s1055-7903(02)00208-7|pmid=12220977 |bibcode=2002MolPE..24..358M }} 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.{{cite journal|last=Finnerty |first=J.R. |author2=Pang, K. |author3=Burton, P. |author4=Paulson, D. |author5=Martindale, M.Q. |title=Origins of bilateral symmetry: Hox and dpp expression in a sea anemone |journal=Science|date=28 May 2004|volume=304 |issue=5675|pages=1335–1337 |doi=10.1126/science.1091946 |pmid=15131263|bibcode=2004Sci...304.1335F |s2cid=21555976 |doi-access=free }}

The differing definitions assigned by zoologists are listed in the table.

class="wikitable sortable"
Author	Work	Date	Name of group	Taxa included	Level of group
Cuvier	Le Règne Animal	1817	Zoophytes (Radiata in English translations)	Échinodermes, Intestinaux (parasitic worms), Acalèphes (Ctenophora), Polypes (Cnidaria), Infusoires	Embranchement (1 of 4)
Cavalier-Smith	"A 6-kingdom classification and a unified phylogeny"	1983	Radiata	Myxozoa, Placozoa, Cnidaria, Ctenophora	Subkingdom
Margulis, Schwartz	Five Kingdoms	1988	Radiata	Cnidaria, Ctenophora	Subkingdom
Philippe et al.	"Phylogenomics Revives Traditional Views on Deep Animal Relationships"	2009	Coelenterata	Cnidaria, Ctenophora	Proposed clade