Editing Cnidaria (section)

==Distinguishing features==
{{further|Porifera|Ctenophora|Bilateria|Placozoa}}
Cnidarians form a [[phylum]] of [[animal]]s that are more complex than [[sponge]]s, about as complex as [[ctenophore]]s (comb jellies), and less complex than [[bilateria]]ns, which include almost all other animals. Both cnidarians and ctenophores are more complex than sponges as they have: cells bound by inter-cell connections and carpet-like [[basement membrane]]s; [[muscle]]s; [[nervous system]]s; and '''some''' have [[sensory receptor|sensory]] organs. Cnidarians are distinguished from all other animals by having [[cnidocyte]]s that fire [[harpoon]]-like structures that are mainly used to capture prey. In some species, cnidocytes can also be used as anchors.<ref name="Hinde2001">{{cite book| author=Hinde, R.T.| year=1998| chapter=The Cnidaria and Ctenophora| pages=28–57| editor=Anderson, D.T.| title=Invertebrate Zoology| publisher=Oxford University Press| isbn=978-0-19-551368-4}}</ref> Cnidarians are also distinguished by the fact that they have only one opening in their body for ingestion and excretion i.e. they do not have a separate mouth and anus.

Like sponges and ctenophores, cnidarians have two main layers of cells that sandwich a middle layer of jelly-like material, which is called the [[mesoglea]] in cnidarians; more complex [[animal]]s have three main cell layers and no intermediate jelly-like layer. Hence, cnidarians and ctenophores have traditionally been labelled [[diploblastic]], along with sponges.<ref name="Hinde2001" /><ref name="Ruppert" /> However, both cnidarians and ctenophores have a type of [[muscle]] that, in more complex animals, arises from the [[mesoderm|middle cell layer]].<ref name="Seipel">{{cite journal|author1=Seipel, K. |author2=Schmid, V.| title=Evolution of striated muscle: Jellyfish and the origin of triploblasty| journal=Developmental Biology| volume=282| issue=1| date=June 2005| pages=14–26| doi=10.1016/j.ydbio.2005.03.032| pmid=15936326| doi-access=free}}</ref> As a result, some recent text books classify ctenophores as [[triploblastic]],<ref name="Ruppert" />{{rp|182–195}} and it has been suggested that cnidarians evolved from triploblastic ancestors.<ref name="Seipel"/>

{| class="wikitable" style="margin-left:4px"
! &nbsp;!![[Sponge]]s<ref name="Ruppert" />{{rp|76–97}}<ref>{{cite book| author=Bergquist, P.R.| year=1998| chapter=Porifera| pages=10–27| editor=Anderson, D.T.| title=Invertebrate Zoology| publisher=Oxford University Press| isbn=978-0-19-551368-4}}</ref>!!Cnidarians<ref name="Hinde2001" /><ref name="Ruppert" />!![[Ctenophore]]s<ref name="Hinde2001" /><ref name="Ruppert" />{{rp|182–195}}!![[Bilateria]]<ref name="Hinde2001" />
|- style="text-align:center;"
! [[Cnidocyte]]s
| No||Yes||colspan=2| No
|- style="text-align:center;"
! [[Colloblast]]s
| colspan=2| No||Yes||No
|- style="text-align:center;"
! [[Digestive system|Digestive]] and [[circulatory system|circulatory]] [[organ (anatomy)|organ]]s
| colspan=3| No||Yes
|- style="text-align:center;"
! Number of main cell layers
| Two, with jelly-like layer between them
|Two||Two||Three
|- style="text-align:center;"
! Cells in each layer bound together
| cell-adhesion molecules, but no basement membranes except [[Homoscleromorpha]].<ref>{{cite journal|author1=Exposito, J-Y. |author2=Cluzel, C. |author3=Garrone, R. |author4=Lethias, C. |name-list-style=amp | title=Evolution of collagens| journal=The Anatomical Record Part A: Discoveries in Molecular, Cellular, and Evolutionary Biology| volume=268| pages=302–316| doi=10.1002/ar.10162| year=2002|issue=3| pmid=12382326|s2cid=12376172 |doi-access=free}}</ref>||colspan=3|inter-cell connections; basement membranes
|- style="text-align:center;"
! [[Sensory receptor|Sensory]] organs
| No||colspan=3| Yes
|- style="text-align:center;"
! Number of cells in middle "jelly" layer
| Many||colspan=2| Few||(Not applicable)
|- style="text-align:center;"
! Cells in outer layers can move inwards and change functions
| Yes||colspan=2| No||(Not applicable)
|- style="text-align:center;"
! Nervous system
| No||colspan=2| Yes, simple||Simple to complex
|- style="text-align:center;"
! [[Muscle]]s
| None||Mostly epitheliomuscular||Mostly myoepithelial||Mostly [[myocyte]]s
|}
{{clear}}