Editing Endosymbiont (section)

==== Marine ====
Extracellular endosymbionts are represented in all four extant classes of [[Echinodermata]] ([[Crinoidea]], [[Ophiuroidea]], [[Echinoidea]], and [[Holothuroidea]]). Little is known of the nature of the association (mode of infection, transmission, metabolic requirements, etc.) but [[phylogenetic]] analysis indicates that these symbionts belong to the class [[Alphaproteobacteria]], relating them to ''[[Rhizobium]]'' and ''[[Thiobacillus]]''. Other studies indicate that these subcuticular bacteria may be both abundant within their hosts and widely distributed among the Echinoderms.<ref>{{cite journal |vauthors=Burnett WJ, McKenzie JD |title=Subcuticular bacteria from the brittle star Ophiactis balli (Echinodermata: Ophiuroidea) represent a new lineage of extracellular marine symbionts in the alpha subdivision of the class Proteobacteria |journal=Applied and Environmental Microbiology |volume=63 |issue=5 |pages=1721–1724 |date=May 1997 |pmid=9143108 |pmc=168468 |doi=10.1128/AEM.63.5.1721-1724.1997 |bibcode=1997ApEnM..63.1721B }}</ref>

Some marine [[oligochaeta]] (e.g., ''[[Olavius algarvensis]]'' and ''[[Inanidrilus|Inanidrillus]] spp.'') have obligate extracellular endosymbionts that fill the entire body of their host. These marine worms are nutritionally dependent on their symbiotic [[chemoautotroph]]ic bacteria lacking any digestive or excretory system (no gut, mouth, or [[nephridia]]).<ref>{{cite journal |vauthors=Dubilier N, Mülders C, Ferdelman T, de Beer D, Pernthaler A, Klein M, Wagner M, Erséus C, Thiermann F, Krieger J, Giere O, Amann R |display-authors=6 |title=Endosymbiotic sulphate-reducing and sulphide-oxidizing bacteria in an oligochaete worm |journal=Nature |volume=411 |issue=6835 |pages=298–302 |date=May 2001 |pmid=11357130 |doi=10.1038/35077067 |s2cid=4420931 |bibcode=2001Natur.411..298D }}</ref>

The sea slug ''[[Elysia chlorotica]]'s'' endosymbiont is the [[algae]] ''[[Vaucheria litorea]].'' The [[jellyfish]] ''[[Mastigias]]'' have a similar relationship with an algae. ''[[Elysia chlorotica]]'' forms this relationship intracellularly with the algae's chloroplasts. These chloroplasts retain their photosynthetic capabilities and structures for several months after entering the slug's cells.<ref>{{cite journal |vauthors=Mujer CV, Andrews DL, Manhart JR, Pierce SK, Rumpho ME |title=Chloroplast genes are expressed during intracellular symbiotic association of Vaucheria litorea plastids with the sea slug Elysia chlorotica |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=93 |issue=22 |pages=12333–12338 |date=October 1996 |pmid=8901581 |pmc=37991 |doi=10.1073/pnas.93.22.12333 |bibcode=1996PNAS...9312333M |doi-access=free }}</ref>

''[[Trichoplax]]'' have two bacterial endosymbionts. Ruthmannia lives inside the animal's digestive cells. Grellia lives permanently inside the [[endoplasmic reticulum]] (ER), the first known symbiont to do so.<ref>{{Cite web|url=https://phys.org/news/2019-06-deceptively-simple-minute-marine-animals.html|title=Deceptively simple: Minute marine animals live in a sophisticated symbiosis with bacteria|first=Max Planck|last=Society|website=phys.org}}</ref>

''[[Paracatenula]]'' is a [[flatworm]] which have lived in symbiosis with an endosymbiotic bacteria for 500 million years. The bacteria produce numerous small, droplet-like vesicles that provide the host with needed nutrients.<ref>{{Cite web|url=https://phys.org/news/2019-04-bacterium-entire-flatworm.html|title=How a bacterium feeds an entire flatworm|first=Max Planck|last=Society|website=phys.org}}</ref>

===== Dinoflagellates =====
[[Dinoflagellate]] endosymbionts of the genus ''[[Symbiodinium]]'', commonly known as [[zooxanthella]]e, are found in [[corals]], [[mollusk]]s (esp. [[giant clam]]s, the ''Tridacna''), [[sea sponge|sponges]], and the unicellular [[foraminifera]]. These endosymbionts capture sunlight and provide their hosts with energy via [[carbonate]] deposition.<ref name=Baker2003>{{cite journal |author=Baker AC |s2cid=35278104 |title=Flexibility and Specificity in Coral-Algal Symbiosis: Diversity, Ecology, and Biogeography of Symbiodinium |journal=Annual Review of Ecology, Evolution, and Systematics |volume=34 |pages=661–89 |date=November 2003 |doi=10.1146/annurev.ecolsys.34.011802.132417 }}</ref>

Previously thought to be a single species, molecular [[phylogenetic]] evidence reported diversity in ''Symbiodinium''. In some cases, the host requires a specific ''Symbiodinium'' [[clade]]. More often, however, the distribution is ecological, with symbionts switching among hosts with ease. When reefs become environmentally stressed, this distribution is related to the observed pattern of [[coral bleaching]] and recovery. Thus, the distribution of ''Symbiodinium'' on coral reefs and its role in coral bleaching is an important in coral reef ecology.<ref name=Baker2003/>