Editing Jellyfish (section)

==== Utility as a model organism ====
Box jellyfish eyes are a visual system that is sophisticated in numerous ways. These intricacies include the considerable variation within the [[Morphology (biology)|morphology]] of box jellyfishes' eyes (including their task/behavior specification), and the [[Molecule|molecular]] makeup of their eyes including: photoreceptors, [[opsin]]s, lenses, and [[synapse]]s.<ref name="Garm-2010" /> The comparison of these attributes to more derived visual systems can allow for a further understanding of how the evolution of more derived visual systems may have occurred, and puts into perspective how box jellyfish can play the role as an [[Evolutionary developmental biology|evolutionary/developmental]] model for all visual systems.<ref name="Piatigorsky-2004">{{cite journal|vauthors=Piatigorsky J, Kozmik Z |title=Cubozoan jellyfish: an Evo/Devo model for eyes and other sensory systems |journal=Int. J. Dev. Biol. |volume=48 |pages=719–729 |year=2004 |issue=8–9 |doi=10.1387/ijdb.041851jp|pmid=15558464 |doi-access=free }}</ref>

===== Characteristics =====
Box jellyfish visual systems are both diverse and complex, comprising multiple [[photosystem]]s.<ref name="Garm-2010" /> There is likely considerable variation in visual properties between species of box jellyfish given the significant [[Hybrid (biology)|inter-species]] morphological and [[Physiology|physiological]] variation. Eyes tend to differ in size and shape, along with number of receptors (including [[opsin]]s), and physiology across species of box jellyfish.<ref name="Garm-2010" />

Box jellyfish have a series of intricate lensed eyes that are similar to those of more derived multicellular organisms such as vertebrates. Their 24 eyes fit into four different morphological categories.<ref name="Gray-2009">{{cite journal|vauthors=Gray GC, Martin VJ, Satterlie RA |title=Ultrastructure of the retinal synapses in cubozoans |journal=Biol Bull |date= Aug 2009 |volume=217 |issue=1 |pages=35–49 |doi=10.1086/BBLv217n1p35 |pmid=19679721|s2cid=24400231 |url=http://libres.uncg.edu/ir/uncw/f/grayg2007-1.pdf }}</ref> These categories consist of two large, morphologically different medial eyes (a lower and upper lensed eye) containing spherical lenses, a lateral pair of pigment slit eyes, and a lateral pair of pigment pit eyes.<ref name="O'Connor-2009" /> The eyes are situated on [[Rhopalium|rhopalia]] (small sensory structures) which serve sensory functions of the box jellyfish and arise from the cavities of the exumbrella (the surface of the body) on the side of the bells of the jellyfish.<ref name="Garm-2010" /> The two large eyes are located on the mid-line of the club and are considered complex because they contain lenses. The four remaining eyes lie laterally on either side of each rhopalia and are considered simple. The simple eyes are observed as small invaginated cups of [[epithelium]] that have developed [[pigment]]ation.<ref name="Berger-1898">{{cite journal|author=Berger, Edward W |title=The Histological Structure of the Eyes of Cubomedusae |journal=Journal of Comparative Neurology |volume=8 |issue=3 |year=1898 |pages=223–230 |doi=10.1002/cne.910080317|s2cid=85422599 |url=https://zenodo.org/record/2067109 }}</ref> The larger of the complex eyes contains a cellular [[cornea]] created by a mono ciliated epithelium, cellular lens, homogenous capsule to the lens, [[vitreous body]] with prismatic elements, and a [[retina]] of pigmented cells. The smaller of the complex eyes is said to be slightly less complex given that it lacks a capsule but otherwise contains the same structure as the larger eye.<ref name="Berger-1898" />

Box jellyfish have multiple photosystems that comprise different sets of eyes.<ref name="Garm-2010" /> Evidence includes [[Immunocytochemistry|immunocytochemical]] and molecular data that show [[photopigment]] differences among the different morphological eye types, and physiological experiments done on box jellyfish to suggest behavioral differences among photosystems. Each individual eye type constitutes photosystems that work collectively to control visually guided behaviors.<ref name="Garm-2010" />

Box jellyfish eyes primarily use c-PRCs (ciliary photoreceptor cells) similar to that of vertebrate eyes. These cells undergo [[phototransduction]] cascades (process of light absorption by photoreceptors) that are triggered by c-opsins.<ref>{{cite journal|first1=Hiroshi|last1=Suga|first2=Volker|last2=Schmid|first3=Walter J.|last3=Gehring |title=Evolution and Functional Diversity of Jellyfish Opsins |journal=Current Biology |volume=18 |issue=1 |year=2008 |pages=51–55 |issn=0960-9822 |doi=10.1016/j.cub.2007.11.059|pmid=18160295 |s2cid=13344739 |doi-access=free |bibcode=2008CBio...18...51S }}</ref> Available opsin sequences suggest that there are two types of opsins possessed by all cnidarians including an ancient [[Phylogenetics|phylogenetic]] opsin, and a sister ciliary opsin to the c-opsins group. Box jellyfish could have both ciliary and cnidops (cnidarian opsins), which is something not previously believed to appear in the same retina.<ref name="Garm-2010" /> Nevertheless, it is not entirely evident whether cnidarians possess multiple opsins that are capable of having distinctive [[Spectral sensitivity|spectral sensitivities]].<ref name="Garm-2010" />

===== Comparison with other organisms =====
Comparative research on genetic and molecular makeup of box jellyfishes' eyes versus more derived eyes seen in vertebrates and cephalopods focuses on: lenses and [[crystallin]] composition, [[synapse]]s, and [[Pax genes]] and their implied evidence for shared primordial (ancestral) genes in eye evolution.<ref name="Piatigorsky-1989">{{cite journal|vauthors=Piatigorsky J, Horwitz J, Kuwabara T, Cutress C |title=The Cellular Eye Lens and Crystallins of Cubomedusan Jellyfish |journal=Journal of Comparative Physiology A |volume=164 |issue=5 |year=1989 |pages=577–587 |doi=10.1007/bf00614500|pmid=2565398 |s2cid=19797109 }}</ref>

Box jellyfish eyes are said to be an evolutionary/developmental model of all eyes based on their evolutionary recruitment of crystallins and Pax genes.<ref name="Piatigorsky-2004" /> Research done on box jellyfish including ''[[Tripedalia cystophora]]'' has suggested that they possess a single Pax gene, PaxB. PaxB functions by binding to crystallin promoters and activating them. PaxB [[in situ hybridization]] resulted in PaxB expression in the lens, retina, and [[statocyst]]s.<ref name="Piatigorsky-2004" /> These results and the rejection of the prior hypothesis that Pax6 was an ancestral Pax gene in eyes has led to the conclusion that PaxB was a primordial gene in eye evolution, and that the eyes of all organisms likely share a common ancestor.<ref name="Piatigorsky-2004" />

The lens structure of box jellyfish appears very similar to those of other organisms, but the crystallins are distinct in both function and appearance.<ref name="Piatigorsky-1989" /> Weak reactions were seen within the sera and there were very weak sequence similarities within the crystallins among vertebrate and invertebrate lenses.<ref name="Piatigorsky-1989" /> This is likely due to differences in lower molecular weight proteins and the subsequent lack of [[Immunology|immunological]] reactions with [[Antiserum|antisera]] that other organisms' lenses exhibit.<ref name="Piatigorsky-1989" />

All four of the visual systems of box jellyfish species investigated with detail (''[[Carybdea marsupialis]], [[Chiropsalmus quadrumanus]], [[Tamoya haplonema]] and Tripedalia cystophora'') have invaginated synapses, but only in the upper and lower lensed eyes. Different densities were found between the upper and lower lenses, and between species.<ref name="Gray-2009" /> Four types of chemical synapses have been discovered within the rhopalia which could help in understanding neural organization including: clear unidirectional, dense-core unidirectional, clear bidirectional, and clear and dense-core bidirectional. The synapses of the lensed eyes could be useful as markers to learn more about the neural circuit in box jellyfish retinal areas.<ref name="Gray-2009" />