View source for Biology:Coelenterata

{{Short description|Term encompassing animal phyla Cnidaria and Ctenophora}}
{{automatic_Taxobox
| name = Coelenterates
| image= Comb_jellies-mba.jpg
| image_caption = [[Biology:Ctenophora|Comb jellies]] (''Beroe'' spp.)
| taxon= Coelenterata
| authority = Hatschek, 1888
| subdivision_ranks = [[Biology:Phylum|Phyla]]
| subdivision = 
*[[Biology:Ctenophora|Ctenophora]]
*[[Biology:Cnidaria|Cnidaria]]
}}

'''Coelenterata''' is a term encompassing the animal [[Biology:Phylum|phyla]] [[Biology:Cnidaria|Cnidaria]] ([[Biology:Coral|coral]] animals, true jellies, sea anemones, [[Biology:Sea pen|sea pen]]s, and their relatives) and [[Biology:Ctenophora|Ctenophora]] (comb jellies). The name comes {{etymology|grc|''{{wikt-lang|grc|κοῖλος}}'' ({{grc-transl|κοῖλος}})|hollow||''{{wikt-lang|grc|ἔντερον}}'' ({{grc-transl|ἔντερον}})|intestine}}, referring to the hollow [[Biology:Body cavity|body cavity]] common to these two phyla.<ref name="OED">{{Cite OED|coelenterate}}</ref><ref name="MW">{{cite Merriam-Webster|coelenterate|access-date=2017-02-25}}</ref> They have very simple [[Biology:Tissue|tissue]] organization, with only two layers of cells ([[Biology:Ectoderm|ectoderm]] and [[Biology:Endoderm|endoderm]]), and radial symmetry. Some examples are [[Biology:Coral|coral]]s, which are typically colonial, and [[Biology:Hydra (genus)|hydrae]], [[Biology:Jellyfish|jellyfish]], and [[Biology:Sea anemone|sea anemone]]s, which are solitary. Coelenterata lack a specialized circulatory system relying instead on diffusion across the tissue layers.

==Characteristics==
All coelenterates are aquatic, mostly [[Biology:Marine life|marine]], animals. The body form is [[Biology:Symmetry in biology|radially symmetrical]], diploblastic and does not have a [[Biology:Coelom|coelom]]. The body has a single opening, the {{wikt-lang|en|hypostome}}, surrounded by sensory [[Biology:Tentacle|tentacle]]s equipped with either nematocysts or [[Biology:Colloblast|colloblast]]s to capture mostly [[Earth:Plankton|plankton]]ic prey. These tentacles are surrounded by a spacious cavity called the [[Biology:Gastrovascular cavity|gastrovascular cavity]], or coelenteron. Digestion is both intracellular and extracellular. Respiration and excretion are accomplished by simple diffusion. A network of nerves is spread throughout the body. Many Cnidaria exhibit [[Biology:Polymorphism|polymorphism]], wherein different types of individuals are present in a colony for different functions. These individuals are called zooids. These animals generally reproduce asexually by budding, though sexual reproduction does occur in some groups.

==History of classification==
The scientific validity of the term ''coelenterate'' is currently rejected, as the Cnidaria and Ctenophora have less in common than previously assumed.<ref name="Dunn2015">{{cite journal|last1=Dunn|first1=Casey W.|last2=Leys|first2=Sally P.|last3=Haddock|first3=Steven H.D.|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|doi-access=free|pmid=25840473}}</ref> Coelentera may only be monophyletic if both [[Biology:Placozoa|Placozoa]] and [[Biology:Bilateria|Bilateria]] are included.<ref name="Pisani">{{Cite journal|last1=Pisani|first1=Davide|last2=Pett|first2=Walker|last3=Dohrmann|first3=Martin|last4=Feuda|first4=Roberto|last5=Rota-Stabelli|first5=Omar|last6=Philippe|first6=Hervé|last7=Lartillot|first7=Nicolas|last8=Wörheide|first8=Gert|date=2015-12-15|title=Genomic data do not support comb jellies as the sister group to all other animals|journal=Proceedings of the National Academy of Sciences|language=en|volume=112|issue=50|pages=15402–15407|doi=10.1073/pnas.1518127112|issn=0027-8424|pmc=4687580|pmid=26621703|bibcode=2015PNAS..11215402P|doi-access=free}}</ref> In particular, the phylogenetic position of [[Biology:Ctenophora|Ctenophora]] is controversial; it was first considered a sub-group of coelenterata but Hyman regarded it as a separate phylum.<ref name="Pisani" /><ref>{{Cite journal|title = Error, signal, and the placement of Ctenophora sister to all other animals|journal = Proceedings of the National Academy of Sciences|date = 2015-05-05|issn = 0027-8424|pmc = 4426464|pmid = 25902535|pages = 5773–5778|volume = 112|issue = 18|doi = 10.1073/pnas.1503453112|first1 = Nathan V.|last1 = Whelan|first2 = Kevin M.|last2 = Kocot|first3 = Leonid L.|last3 = Moroz|first4 = Kenneth M.|last4 = Halanych|bibcode = 2015PNAS..112.5773W|doi-access = free}}</ref> Most researchers think that Coelenterata is not [[Biology:Monophyly|monophyletic]], and therefore any group containing Cnidaria and Ctenophora but excluding other phyla would be paraphyletic. 

Previously, some genomic studies have found support for monophyletic coelenterates.<ref name="Philippe2009">{{Cite journal|title = Phylogenomics Revives Traditional Views on Deep Animal Relationships|journal = Current Biology|issn = 0960-9822|pmid = 19345102|pages = 706–712|volume = 19|issue = 8|doi = 10.1016/j.cub.2009.02.052|first1 = Hervé|last1 = Philippe|first2 = Romain|last2 = Derelle|first3 = Philippe|last3 = Lopez|first4 = Kerstin|last4 = Pick|first5 = Carole|last5 = Borchiellini|first6 = Nicole|last6 = Boury-Esnault|first7 = Jean|last7 = Vacelet|first8 = Emmanuelle|last8 = Renard|first9 = Evelyn|last9 = Houliston|date=April 2009|doi-access = free}}</ref><ref>{{Cite journal|title = Deep metazoan phylogeny: When different genes tell different stories|journal = Molecular Phylogenetics and Evolution|date = 2013-04-01|pages = 223–233|volume = 67|issue = 1|doi = 10.1016/j.ympev.2013.01.010|first1 = Tetyana|last1 = Nosenko|first2 = Fabian|last2 = Schreiber|first3 = Maja|last3 = Adamska|first4 = Marcin|last4 = Adamski|first5 = Michael|last5 = Eitel|first6 = Jörg|last6 = Hammel|first7 = Manuel|last7 = Maldonado|first8 = Werner E. G.|last8 = Müller|first9 = Michael|last9 = Nickel|pmid=23353073}}</ref>  Despite this uncertainty, the term ''coelenterate'' is still used in informal settings to refer to the Cnidaria and Ctenophora.

Complicating the issue is the 1997 work of [[Biography:Lynn Margulis|Lynn Margulis]] (revising an earlier model by [[Biography:Thomas Cavalier-Smith|Thomas Cavalier-Smith]]) that placed the Cnidaria and Ctenophora alone in the branch [[Biology:Radiata|Radiata]] within [[Biology:Eumetazoa|Eumetazoa]].<ref>Margulis, Lynn and Karlene V. Schwartz, 1997, ''Five Kingdoms: An Illustrated Guide to the Phyla of Life on Earth'', W.H. Freeman & Company, {{ISBN|0-613-92338-3}}</ref> (The latter refers to all the animals except the [[Biology:Porifera|sponges]], [[Biology:Trichoplax|Trichoplax]], and the still poorly understood [[Biology:Mesozoa|Mesozoa]]). Neither grouping is accepted universally,<ref>{{Cite web|url=https://www.ncbi.nlm.nih.gov/Taxonomy/Browser/wwwtax.cgi?mode=Tree&id=6072&lvl=3&p=mapview&p=has_linkout&p=blast_url&p=genome_blast&lin=f&keep=1&srchmode=1&unlock|title=Taxonomy browser (Eumetazoa)|website=www.ncbi.nlm.nih.gov}}</ref> however, both are commonly encountered in taxonomic literature.<ref name="Dunn2015"/><ref name="Philippe2009"/>

==References==
{{Reflist}}

{{Taxonbar|from=Q387474}}

[[Category:Cnidarian taxonomy]]

{{Sourceattribution|Coelenterata}}