Editing Cnidaria (section)

===Nervous system and senses===
Cnidarians are generally thought to have no brains or even central nervous systems. However, they do have integrative areas of neural tissue that could be considered some form of centralization. Most of their bodies are innervated by decentralized nerve nets that control their swimming musculature and connect with sensory structures, though each clade has slightly different structures.<ref name=Central>{{Cite journal|last=Satterlie|first=Richard A.|date=15 April 2011|title=Do jellyfish have central nervous systems?|journal=Journal of Experimental Biology|language=en|volume=214|issue=8|pages=1215–1223|doi=10.1242/jeb.043687|issn=0022-0949|pmid=21430196|doi-access=free|bibcode=2011JExpB.214.1215S }}</ref> These sensory structures, usually called rhopalia, can generate signals in response to various types of stimuli such as light, pressure, chemical changes, and much more. Medusa usually have several of them around the margin of the bell that work together to control the motor nerve net, that directly innervates the swimming muscles. Most cnidarians also have a parallel system. In scyphozoans, this takes the form of a diffuse nerve net, which has modulatory effects on the nervous system.<ref name=Control>{{Cite journal|last=Satterlie|first=Richard A|s2cid=18244609|date=2002-10-01|title=Neuronal control of swimming in jellyfish: a comparative story|journal=Canadian Journal of Zoology|volume=80|issue=10|pages=1654–1669|doi=10.1139/z02-132|bibcode=2002CaJZ...80.1654S |issn=0008-4301}}</ref> As well as forming the "signal cables" between sensory neurons and motoneurons, intermediate neurons in the nerve net can also form ganglia that act as local coordination centers. Communication between nerve cells can occur by chemical synapses or gap junctions in hydrozoans, though gap junctions are not present in all groups. Cnidarians have many of the same neurotransmitters as bilaterians, including chemicals such as glutamate, GABA, and glycine.<ref>{{Cite journal|last1=Kass-Simon|first1=G.|last2=Pierobon|first2=Paola|date=1 January 2007|title=Cnidarian chemical neurotransmission, an updated overview|journal=Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology|volume=146|issue=1|pages=9–25|doi=10.1016/j.cbpa.2006.09.008|pmid=17101286}}</ref> Serotonin, dopamine, noradrenaline, octopamine, histamine, and acetylcholine, on the other hand, are absent.<ref>[https://www.frontiersin.org/articles/10.3389/fcell.2022.1071961/full What is a neuron? (Ctenophores, sponges and placozoans)]</ref>

This structure ensures that the musculature is excited rapidly and simultaneously, and can be directly stimulated from any point on the body, and it also is better able to recover after injury.<ref name=Central/><ref name=Control />

Medusae and complex swimming colonies such as [[siphonophore]]s and [[chondrophore]]s sense tilt and acceleration by means of [[statocyst]]s, chambers lined with hairs which detect the movements of internal mineral grains called statoliths. If the body tilts in the wrong direction, the animal rights itself by increasing the strength of the swimming movements on the side that is too low. Most species have [[ocelli]] ("simple eyes"), which can detect sources of light. However, the agile [[box jellyfish]] are unique among Medusae because they possess four kinds of true eyes that have [[retinas]], [[cornea]]s and [[lens (anatomy)|lenses]].<ref name="live">{{cite web|url=http://www.livescience.com/7243-jellyfish-human-eyes.html|title=Jellyfish Have Human-Like Eyes|publisher=www.livescience.com|date=April 1, 2007|access-date=2012-06-12}}</ref> Although the eyes probably do not form images, Cubozoa can clearly distinguish the direction from which light is coming as well as negotiate around solid-colored objects.<ref name="Hinde2001" /><ref name="live" />