Editing Zooplankton (section)

===Metazoa (animals)===
[[File:Fish3562 - Flickr - NOAA Photo Library.jpg|thumb|{{center|Octopus larva and pteropod}}]]

Free-living species in the crustacean class [[Copepod]]a are typically 1 to 2&nbsp;mm long with teardrop-shaped bodies. Like all crustaceans, their bodies are divided into three sections: head, thorax, and abdomen, with two pairs of antennae; the first pair is often long and prominent. They have a tough [[exoskeleton]] made of calcium carbonate and usually have a [[Crustacean larva#Nauplius|single red eye]] in the centre of their transparent head.<ref name=IZ>{{cite book |author=Robert D. Barnes |year=1982 |title= Invertebrate Zoology |publisher= Holt-Saunders International |location=[[Philadelphia, Pennsylvania]] |pages=683–692 |isbn=978-0-03-056747-6}}</ref> About 13,000 species of copepods are known, of which about 10,200 are marine.<ref>{{Cite web |url=http://www.marinespecies.org/aphia.php?p=taxdetails&id=1080 |title=WoRMS - World Register of Marine Species - Copepoda |website=www.marinespecies.org |access-date=2019-06-28 |archive-url=https://web.archive.org/web/20190630192104/http://www.marinespecies.org/aphia.php?p=taxdetails&id=1080 |archive-date=2019-06-30 |url-status=live}}</ref><ref>{{cite journal |author1=Geoff A. Boxhall |author2=Danielle Defaye |year=2008 |title=Global diversity of copepods (Crustacea: Copepoda) in freshwater |journal=[[Hydrobiologia]] |volume=595 |issue=1 |pages=195–207 |doi=10.1007/s10750-007-9014-4 |s2cid=31727589 }}</ref> They are usually among the more dominant members of the zooplankton.<ref>{{cite web |author1=Johannes Dürbaum |author2=Thorsten Künnemann |date=November 5, 1997 |title=Biology of Copepods: An Introduction |url=http://www.uni-oldenburg.de/zoomorphology/Biologyintro.html |publisher=[[Carl von Ossietzky University of Oldenburg]] |access-date=December 8, 2009 |url-status=dead |archive-url=https://web.archive.org/web/20100526164720/http://www.uni-oldenburg.de/zoomorphology/Biologyintro.html |archive-date=May 26, 2010 }}</ref>

In addition to copepods the crustacean classes [[ostracod]]s, [[Branchiopoda|branchiopods]] and [[malacostraca]]ns also have planktonic members. [[Barnacle]]s are planktonic only during the larval stage.<ref>[https://books.google.com/books?id=5kv3AwAAQBAJ&dq=pelagic+realm+significant+crustaceans+pelagic+fauna+Ostracoda+Copepoda&pg=PA25 Treatise on Zoology – Anatomy, Taxonomy, Biology. The Crustacea]</ref>

<gallery mode="packed" heights="120px" caption="[[Metazoan]] zooplankton" style="float:left">
File:Copepod 2 with eggs.jpg| [[Copepod]] with eggs
File:Tomopteriskils.jpg|[[Segmented worm]]
File:Hyperia.jpg| [[Amphipod]]
File:Krill666.jpg| [[Krill]] 
File:Glaucus atlanticus 1 cropped.jpg| [[Glaucus atlanticus|Blue ocean slug]]
</gallery>
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====Holoplankton and meroplankton====
====Ichthyoplankton====
[[Ichthyoplankton]] are the [[Fish eggs|eggs]] and [[larvae]] of fish ("ichthyo" comes from the Greek word for ''fish''). They are planktonic because they cannot swim effectively under their own power, but must drift with the ocean currents. Fish eggs cannot swim at all, and are unambiguously planktonic. Early stage larvae swim poorly, but later stage larvae swim better and cease to be planktonic as they grow into [[juvenile fish]]. Fish larvae are part of the zooplankton that eat smaller plankton, while fish eggs carry their own food supply. Both eggs and larvae are themselves eaten by larger animals.<ref name="NOAA">{{Cite web |date=2007-09-03 |title=What are Ichthyoplankton? |url=https://swfsc.noaa.gov/textblock.aspx?Division=FRD&id=6210 |url-status=dead |archive-url=https://web.archive.org/web/20180218090243/https://swfsc.noaa.gov/textblock.aspx?Division=FRD&id=6210 |archive-date=2018-02-18 |access-date=2011-07-22 |website=Southwest Fisheries Science Center}}</ref><ref name=Moser2006>{{Cite book|url=https://books.google.com/books?id=Qdzg0Vfql2sC&pg=PA269|title = The Ecology of Marine Fishes: California and Adjacent Waters|pages = 269–319|isbn = 9780520932470|last1 = Allen|first1 = Dr. Larry G.|last2 = Horn|first2 = Dr. Michael H.|date = 15 February 2006| publisher=University of California Press }}</ref>

<gallery mode="packed" heights="120px" style="float:left">
File:Squidu.jpg| Juvenile planktonic [[squid]]
File:Molalavdj.jpg| [[Ocean sunfish]] larvae (2.7mm)
File:FMIB 47039 Ostracion hoops.jpeg| [[Boxfish]] larva
</gallery>
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====Gelatinous zooplankton====
[[Gelatinous zooplankton]] include [[ctenophore]]s, [[Jellyfish|medusae]], [[salps]], and [[Chaetognatha]] in coastal waters. Jellyfish are slow swimmers, and most species form part of the plankton. Traditionally jellyfish have been viewed as [[Trophic level|trophic]] dead ends, minor players in the [[marine food web]], gelatinous organisms with a [[body plan]] largely based on water that offers little nutritional value or interest for other organisms apart from a few specialised predators such as the [[ocean sunfish]] and the [[leatherback sea turtle]].<ref name=Hamilton2016>Hamilton, G. (2016) [https://www.nature.com/news/polopoly_fs/1.19613!/menu/main/topColumns/topLeftColumn/pdf/531432a.pdf "The secret lives of jellyfish: long regarded as minor players in ocean ecology, jellyfish are actually important parts of the marine food web"]. ''Nature'', '''531'''(7595): 432–435. {{doi|10.1038/531432a}}</ref><ref name=Hays2018>[[Graeme Hays|Hays, G.C.]], Doyle, T.K. and Houghton, J.D. (2018) "A paradigm shift in the trophic importance of jellyfish?" ''Trends in ecology & evolution'', '''33'''(11): 874–884. {{doi|10.1016/j.tree.2018.09.001}}</ref> 

That view has recently been challenged. Jellyfish, and more gelatinous zooplankton in general, which include [[salp]]s and [[ctenophore]]s, are very diverse, fragile with no hard parts, difficult to see and monitor, subject to rapid population swings and often live inconveniently far from shore or deep in the ocean. It is difficult for scientists to detect and analyse jellyfish in the guts of predators, since they turn to mush when eaten and are rapidly digested.<ref name=Hamilton2016/> But jellyfish bloom in vast numbers, and it has been shown they form major components in the diets of [[tuna]], [[Tetrapturus|spearfish]] and [[swordfish]] as well as various birds and invertebrates such as [[octopus]], [[sea cucumber]]s, [[crab]]s and [[amphipod]]s.<ref>Cardona, L., De Quevedo, I.Á., Borrell, A. and Aguilar, A. (2012) "Massive consumption of gelatinous plankton by Mediterranean apex predators". ''PLOS ONE'', '''7'''(3): e31329. {{doi|10.1371/journal.pone.0031329}}</ref><ref name=Hays2018 /> "Despite their low energy density, the contribution of jellyfish to the energy budgets of predators may be much greater than assumed because of rapid digestion, low capture costs, availability, and selective feeding on the more energy-rich components. Feeding on jellyfish may make marine predators susceptible to ingestion of plastics."<ref name=Hays2018 /> According to a 2017 study, [[narcomedusae]] consume the greatest diversity of mesopelagic prey, followed by [[physonect]] [[siphonophore]]s, [[ctenophore]]s and [[cephalopod]]s.<ref name=Choy2017 /> 

<gallery mode="packed" heights="120px" style="float:left">
File:Parumbrosa polylobata 01.jpg| [[Jellyfish]]
File:Tunicate off Atauro island.jpg| This free-floating [[pyrosome]] is made up of hundreds of individual [[bioluminescent]] tunicates
File:23 salpchain frierson odfw (8253212250).jpg|[[Salp]] chain
</gallery>
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The importance of the so-called "jelly web" is only beginning to be understood, but it seems medusae, ctenophores and siphonophores can be key predators in deep pelagic food webs with ecological impacts similar to predator fish and squid. Traditionally gelatinous predators were thought ineffectual providers of marine trophic pathways, but they appear to have substantial and integral roles in deep [[pelagic food webs]].<ref name=Choy2017>Choy, C.A., Haddock, S.H. and Robison, B.H. (2017) "Deep pelagic food web structure as revealed by ''in situ'' feeding observations". ''Proceedings of the Royal Society B: Biological Sciences'', '''284'''(1868): 20172116. {{doi|10.1098/rspb.2017.2116}}. [[File:CC-BY icon.svg|50px]] Material was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].</ref>