View source for Riftia

{{short description|Giant tube worm (species of annelid)}}
{{Distinguish|Giant tube worm (shipworm)}}
{{italic title}}
{{Speciesbox
| name = Giant tube worms
| image = Riftia tube worm colony Galapagos 2011.jpg
| image_upright = 1.1
| taxon = Riftia pachyptila
| parent_authority = M. L. Jones, 1981
| authority = M. L. Jones, 1981
}}

'''''Riftia pachyptila''''', commonly known as the '''giant tube worm''' and less commonly known as the '''giant beardworm''', is a  [[ocean|marine]] [[invertebrate]] in the [[phylum (biology)|phylum]] [[Annelid]]a<ref>{{cite book |title=Invertebrate Zoology: A functional Evolutionary Approach |edition=7th | vauthors = Ruppert E, Fox R, Barnes R |year=2007 |publisher=Thomson Learning |location=Belmont |isbn=978-0-03-025982-1 |url-access=registration |url=https://archive.org/details/isbn_9780030259821 }}</ref> (formerly grouped in phylum [[Siboglinidae|Pogonophora]] and [[Vestimentifera]]) related to [[tube worm (body plan)|tube worm]]s commonly found in the [[foreshore|intertidal]] and [[pelagic zone]]s. ''R. pachyptila'' lives on the floor of the [[Pacific Ocean]] near [[hydrothermal vent]]s. The vents provide a natural ambient temperature in their environment ranging from 2 to 30&nbsp;°C,<ref name=Bright2008>{{cite book | vauthors = Bright M, Lallier FH | title = Oceanography and Marine Biology | chapter = The biology of vestimentiferan tubeworms | volume = 48 | pages = 213–266 | publisher = [[Taylor & Francis]] | year = 2010 | url = http://www.sb-roscoff.fr/Ecchis/pdf/10-Bright-OMBAR.pdf | access-date = 30 October 2013 | doi = 10.1201/ebk1439821169-c4 | url-status = dead | archive-url = https://web.archive.org/web/20131031234950/http://www.sb-roscoff.fr/Ecchis/pdf/10-Bright-OMBAR.pdf | archive-date = 31 October 2013 | series = Oceanography and Marine Biology - an Annual Review | doi-broken-date = 2024-11-12 | isbn = 978-1-4398-2116-9 }}</ref> and this organism can tolerate extremely high [[hydrogen sulfide]] levels. These worms can reach a length of {{convert|3|m|ftin|abbr=on}},<ref name=McClain>{{Cite journal|last1=McClain|first1=Craig R.|last2=Balk|first2=Meghan A.|last3=Benfield|first3=Mark C.|last4=Branch|first4=Trevor A.|last5=Chen|first5=Catherine|last6=Cosgrove|first6=James|last7=Dove|first7=Alistair D.M.|last8=Gaskins|first8=Lindsay C.|last9=Helm|first9=Rebecca R.|date=2015-01-13|title=Sizing ocean giants: patterns of intraspecific size variation in marine megafauna|journal=PeerJ|language=en|volume=3|page=e715|doi=10.7717/peerj.715 |pmc=4304853|pmid=25649000 |doi-access=free }}</ref> and their tubular bodies have a diameter of {{convert|4|cm|ftin|abbr=on}}.

Its [[common name]] "giant tube worm" is, however, also applied to the largest living species of [[Shipworms|shipworm]], ''[[Kuphus polythalamius]]'', which despite the name "worm", is a [[bivalve]] [[mollusc]] rather than an [[annelid]].

==Discovery==
[[File:330-PSA-139-64 (USN 1097019) (22754473376).jpg|thumb|upright|left|DSV'' [[DSV Alvin|Alvin]]'', the Navy research submarine]]
''R. pachyptila'' was discovered in 1977 on an expedition of the American bathyscaphe [[DSV Alvin|DSV ''Alvin'']] to the [[Galápagos hotspot|Galápagos Rift]] led by geologist [[Jack Corliss]].<ref>{{cite web |url=https://naturalhistory.si.edu/onehundredyears/featured_objects/Riftia.html |title=Giant Tube Worm: Riftia pachyptila |author=<!--Not stated--> |date=<!--Not stated--> |website=Smithsonian National Museum of Natural History |access-date=25 October 2018 |archive-url=https://web.archive.org/web/20181024201537/https://naturalhistory.si.edu/onehundredyears/featured_objects/Riftia.html |archive-date=24 October 2018 |url-status=dead }}</ref> The discovery was unexpected, as the team was studying hydrothermal vents and no biologists were included in the expedition. Many of the species found living near hydrothermal vents during this expedition had never been seen before.

At the time, the presence of thermal springs near the midoceanic ridges was known. Further research uncovered aquatic life in the area, despite the high temperature (around 350–380&nbsp;°C).<ref>{{cite web|url=https://pubs.usgs.gov/gip/dynamic/exploring.html|title=Exploring the deep ocean floor: Hot springs and strange creatures }}</ref><ref>{{cite journal| vauthors = Koschinsky A, Garbe-Schönberg D, Sander S, Schmidt K, Gennerich HH, Strauss H |date=2008|title=Hydrothermal venting at pressure-temperature conditions above the critical point of seawater, 5°S on the Mid-Atlantic Ridge|journal=Geology|volume=36|issue=8|page=615|doi=10.1130/g24726a.1 |bibcode=2008Geo....36..615K}}</ref>

Many samples were collected, including bivalves, polychaetes, large crabs, and ''R. pachyptila''.<ref>{{cite journal|last=Childress|first=James J. | name-list-style = vanc |date=October 1988|title=Biology and chemistry of a deep-sea hydrothermal vent on the Galapagos Rift; the Rose Garden in 1985. Introduction|journal=Deep Sea Research Part A. Oceanographic Research Papers|language=en|volume=35|issue=10–11|pages=1677–1680|doi=10.1016/0198-0149(88)90043-X|bibcode=1988DSRA...35.1677C}}</ref><ref>{{cite journal|last=Lutz|first=Richard|name-list-style=vanc|date=1 January 1991|title=The biology of deep-sea vents and seeps: Alvin's magical mystery tour|url=https://www.researchwithnj.com/en/publications/the-biology-of-deep-sea-vents-and-seeps-alvins-magical-mystery-to|journal=Oceanus|volume=34|issue=4|pages=75–83|issn=0029-8182|access-date=22 December 2019|archive-url=https://web.archive.org/web/20191222200354/https://www.researchwithnj.com/en/publications/the-biology-of-deep-sea-vents-and-seeps-alvins-magical-mystery-to|archive-date=22 December 2019|url-status=dead}}</ref> It was the first time that species was observed.

==Development==
''R. pachyptila'' develops from a free-swimming, [[pelagic]], nonsymbiotic [[trochophore]] larva, which enters juvenile ([[metatrochophore]]) development, becoming [[sessility (zoology)|sessile]], and subsequently acquiring symbiotic bacteria.<ref name=Bright>{{cite web |url=http://www.hydrothermalvent.com/php/index.php?option=com_content&view=article&id=46:riftia-pachyptila&catid=12:symbiosis&Itemid=19 |vauthors=Bright M |title=Riftia pachyptila |access-date=2015-03-19 |archive-url=https://web.archive.org/web/20150402114736/http://www.hydrothermalvent.com/php/index.php?option=com_content&view=article&id=46:riftia-pachyptila&catid=12:symbiosis&Itemid=19|archive-date=2015-04-02|url-status=dead}}</ref><ref>{{cite web |vauthors=Adams DK, Arellano SM, Govenar B |date=Mar 2012 |title=Larval dispersal: Vent life in the ocean column |url=http://darchive.mblwhoilibrary.org/bitstream/handle/1912/5160/25-1_adams.pdf?sequence=1&isAllowed=y |publisher=Oceanography}}</ref> The symbiotic bacteria, on which adult worms depend for sustenance, are not present in the gametes, but are acquired from the environment through the skin in a process akin to an infection. The digestive tract transiently connects from a mouth at the tip of the ventral medial process to a foregut, midgut, hindgut, and anus and was previously thought to have been the method by which the bacteria are introduced into adults.  After symbionts are established in the midgut, they undergo substantial remodelling and enlargement to become the [[trophosome]], while the remainder of the digestive tract has not been detected in adult specimens.<ref name="Jones 1989">{{cite journal |vauthors=Jones ML, Gardiner SL |title=On the early development of the vestimentiferan tube worm ''Ridgeia'' sp. and observations on the nervous system and trophosome of ''Ridgeia'' sp. and ''Riftia pachyptila'' |url=http://www.biolbull.org/content/177/2/254.full.pdf |journal=Biological Bulletin |volume=177| issue=2 |pages=254–276 |date=Oct 1989 |doi=10.2307/1541941 |jstor=1541941 |access-date=2015-03-19 |url-status=dead |archive-date=2015-09-23 |archive-url=https://web.archive.org/web/20150923202155/http://www.biolbull.org/content/177/2/254.full.pdf}}</ref>

==Body structure==
Isolating the vermiform body from white chitinous tube, a small difference exists from the classic three subdivisions typical of phylum [[Siboglinidae|Pogonophora]]:<ref>{{cite journal|last=De Beer | first = Gavin | name-list-style = vanc |date=November 1955|title=The Pogonophora |journal=Nature |volume=176 |issue=4488|page=888|doi=10.1038/176888a0 |bibcode=1955Natur.176..888D| s2cid = 4198316 |doi-access=free }}</ref> the prosoma, the [[mesosoma]], and the [[metasoma]].

[[File:Tube worms ASHES hydrothermal field (27260324626).jpg|thumb|''R. pachyptila'' community with extroflexion of red branchial plume]] 
The first body region is the [[wiktionary:vascular|vascularized]] '''branchial plume''', which is bright red due to the presence of [[hemoglobin]] that contain up to 144 globin chains (each presumably including associated heme structures). These tube worm hemoglobins are remarkable for carrying oxygen in the presence of sulfide, without being inhibited by this molecule, as hemoglobins in most other species are.<ref>{{cite journal | vauthors = Zal F, Lallier FH, Green BN, Vinogradov SN, Toulmond A | title = The multi-hemoglobin system of the hydrothermal vent tube worm ''Riftia pachyptila''. II. Complete polypeptide chain composition investigated by maximum entropy analysis of mass spectra | journal = The Journal of Biological Chemistry | volume = 271 | issue = 15 | pages = 8875–81 | date = April 1996 | pmid = 8621529 | doi = 10.1074/jbc.271.15.8875 | doi-access = free }}</ref><ref name="Hahlbeck_2005">{{cite journal|vauthors=Hahlbeck E, Pospesel MA, Zal F, Childress JJ, Felbeck H|date=July 2005|title=Proposed nitrate binding by hemoglobin in ''Riftia pachyptila''|url=https://www.researchgate.net/publication/237778408 |format=Free full text|journal=Deep-Sea Research Part I: Oceanographic Research Papers|volume=52|issue=10|pages=1885–1895|doi=10.1016/j.dsr.2004.12.011 }}</ref> The plume provides essential nutrients to [[bacteria]] living inside the [[trophosome]]. If the animal perceives a threat or is touched, it retracts the plume and the tube is closed due to the obturaculum, a particular [[Operculum (gastropod)|operculum]] that protects and isolates the animal from the external environment.<ref>{{cite book |last1=Monaco |first1=André |last2=Prouzet |first2=Patrick | name-list-style = vanc |url=https://books.google.com/books?id=U1i-CgAAQBAJ&pg=PA236 |title=Marine Ecosystems: Diversity and Functions |date=2015-10-02 |publisher=John Wiley & Sons |isbn=978-1-119-23246-9 }}</ref>

The second body region is the '''vestimentum''', formed by muscle bands, having a winged shape, and it presents the two genital openings at the end.<ref>{{cite book|url=https://books.google.com/books?id=KZbLHpstfrwC&pg=PA106 |title=Handbook of Deep-sea Hydrothermal Vent Fauna|last1=Desbruyères|first1=Daniel|last2=Segonzac|first2=Michel | name-list-style = vanc |date=1997|publisher=Editions Quae|isbn=978-2-905434-78-4}}</ref><ref>{{cite book|url=https://books.google.com/books?id=70mfDwAAQBAJ&pg=PA2007-IA22 |title=Oceanography and Marine Biology: An Annual Review| vauthors = Gibson RN, Atkinson RJ, Gordon JD |date=2010-05-12|publisher=CRC Press|isbn=978-1-4398-5925-4}}</ref> The heart, extended portion of dorsal vessel, enclose the vestimentum.<ref>{{cite book |url=https://books.google.com/books?id=PGKeXGqqbhsC&pg=PA235 |title=Morphology, Molecules, Evolution and Phylogeny in Polychaeta and Related Taxa | vauthors = Bartolomaeus T, Purschke G |date=2006-03-30 | location = Dordrecht |publisher=Springer Science & Business Media |isbn=978-1-4020-3240-0 }}</ref>

[[File:Nur04507.jpg|thumb|Hydrothermal vent tubeworms get organic compounds from bacteria that live in their [[trophosome]]]]
In the middle part, the '''trunk''' or third body region, is full of vascularized solid tissue, and includes body wall, [[gonad]]s, and the [[coelomic]] cavity. Here is located also the trophosome, spongy tissue where  a billion symbiotic, thioautotrophic bacteria and sulfur granules are found.<ref>{{cite web |url=http://www.biologiamarina.eu/Hydrothermal%20_vents3.html |title=Hydrothermal vents Terza parte |website=www.biologiamarina.eu|access-date=2019-12-10}}</ref><ref name="Stewart_2006">{{cite journal |vauthors=Stewart FJ, Cavanaugh CM |title=Symbiosis of thioautotrophic bacteria with ''Riftia pachyptila'' |journal=Progress in Molecular and Subcellular Biology |volume=41 |pages=197–225 |date=2006 |pmid=16623395 |doi=10.1007/3-540-28221-1_10 |publisher=Springer-Verlag |isbn=978-3-540-28210-5 |veditors=Overmann J}}</ref> Since the mouth, digestive system, and anus are missing, the survival of ''R. pachyptila'' is dependent on this mutualistic symbiosis.<ref name="Cavanaugh_1981">{{cite journal |vauthors=Cavanaugh CM, Gardiner SL, Jones ML, Jannasch HW, Waterbury JB |title=Prokaryotic cells in the hydrothermal vent tube worm ''Riftia pachyptila'' Jones: possible chemoautotrophic symbionts |journal=Science |volume=213 |issue=4505 |pages=340–342 |date=July 1981 |pmid=17819907 |doi=10.1126/science.213.4505.340 |bibcode=1981Sci...213..340C}}</ref> This process, known as [[chemosynthesis]], was recognized within the trophosome by [[Colleen Cavanaugh]].<ref name="Cavanaugh_1981"/>

The soluble hemoglobins, present in the tentacles, are able to bind [[oxygen|O<sub>2</sub>]] and [[hydrogen sulfide|H<sub>2</sub>S]], which are necessary for [[Chemosynthesis|chemosynthetic]] bacteria. Due to the capillaries, these compounds are absorbed by bacteria.<ref>{{cite journal| vauthors = Childress J, Fisher CR |date=1992|title=The biology of hydrothermal vent animals: physiology, biochemistry, and autotrophic symbioses|url=http://www.vliz.be/en/imis?module=ref&refid=212226&printversion=1&dropIMIStitle=1|journal=Oceanography and Marine Biology: An Annual Review}}</ref> During the chemosynthesis, the mitochondrial enzyme [[Rhodanese|rhodanase]] catalyzes the disproportionation reaction of the thiosulfate anion S<sub>2</sub>O<sub>3</sub><sup>2-</sup> to sulfur S and sulfite SO<sub>3</sub><sup>2-</sup> .<ref>{{cite journal|last=Corbera|first=Jordi| name-list-style = vanc |date=2017-04-21|title=La vida que brolla a la foscor: les fumaroles hidrotermals submarines|url=https://www.raco.cat/index.php/Atzavara/article/view/320788|journal=L'Atzavara |volume=27|pages=39–53|issn=2339-9791}}</ref><ref>{{cite journal| vauthors = Simon V, Purcarea C, Sun K, Joseph J, Frebourg G, Lechaire JP, Gaill F, Hervé G |date=2000-01-18|title=The enzymes involved in synthesis and utilization of carbamylphosphate in the deep-sea tube worm ''Riftia pachyptila''|journal=Marine Biology|volume=136|issue=1|pages=115–127|doi=10.1007/s002270050014|bibcode=2000MarBi.136..115S |s2cid=85309709 }}</ref> The ''R. pachyptila''’s bloodstream is responsible for absorption of the  O<sub>2</sub> and nutrients such as carbohydrates.

Nitrate and nitrite are toxic, but are required for biosynthetic processes. The chemosynthetic bacteria within the trophosome convert nitrate to [[ammonium]] ions, which then are available for production of amino acids in the bacteria, which are in turn released to the tube worm. To transport nitrate to the bacteria, ''R. pachyptila'' concentrates nitrate in its blood, to a concentration 100 times more concentrated than the surrounding water. The exact mechanism of ''R. pachyptila''’s ability to withstand and concentrate nitrate is still unknown.<ref name="Hahlbeck_2005" />

In the posterior part, the fourth body region, is the '''opistosome''', which anchors the animal to the tube and is used for the storage of waste from bacterial reactions.<ref>{{cite web|url=https://immobilier-haute-garonne.info/relationship-between-and/symbiotic-relationship-between-chemosynthetic-bacteria-and-riftia-tube-worms.php|title=Riftia pachyptila - Wikipedia - Symbiotic relationship between chemosynthetic bacteria and riftia tube worms|language=en-US|access-date=2019-12-10|archive-url=https://web.archive.org/web/20191210163533/https://immobilier-haute-garonne.info/relationship-between-and/symbiotic-relationship-between-chemosynthetic-bacteria-and-riftia-tube-worms.php|archive-date=2019-12-10|url-status=dead}}</ref>

== Symbiosis ==
The discovery of bacterial invertebrate [[chemoautotrophic]] [[symbiosis]], particularly in vestimentiferan tubeworms ''R. pachyptila''<ref name = "Cavanaugh_1981" /> and then in [[Vesicomyidae|vesicomyid]] clams and [[Mytilidae|mytilid]] mussels revealed the chemoautotrophic potential of the [[hydrothermal vent]] tube worm.<ref name="Felbeck_1981">{{cite journal | vauthors = Felbeck H | title = Chemoautotrophic potential of the hydrothermal vent tube worm, ''Riftia pachyptila'' Jones (Vestimentifera) | journal = Science | volume = 213 | issue = 4505 | pages = 336–8 | date = July 1981 | pmid = 17819905 | doi = 10.1126/science.213.4505.336 | bibcode = 1981Sci...213..336F }}</ref> Scientists discovered a remarkable source of nutrition that helps to sustain the conspicuous biomass of invertebrates at vents.<ref name="Felbeck_1981" /> Many studies focusing on this type of symbiosis revealed the presence of chemoautotrophic, endosymbiotic, sulfur-oxidizing bacteria mainly in ''R. pachyptila'',<ref>{{cite journal|last=Thiel|first=Martin| name-list-style = vanc |date=2001-10-17|title=Cindy Lee Van Dover: The ecology of deep-sea hydrothermal vents|journal=Helgoland Marine Research|volume=55|issue=4|pages=308–309|doi=10.1007/s10152-001-0085-8 |doi-access=free}}</ref>  which inhabits extreme environments and is adapted to the particular composition of the mixed volcanic and sea waters.<ref name="zor">{{cite journal|last=Minic|first=Zoran| name-list-style = vanc |date=2004|title=Biochemical and enzymological aspects of the symbiosis between the deep-sea tubeworm ''Riftia pachyptila'' and its bacterial endosymbiont|journal=European Journal of Biochemistry|volume=271|issue=15|pages=3093–102|doi=10.1111/j.1432-1033.2004.04248.x|pmid=15265029|doi-access=free}}</ref> This special environment is filled with inorganic metabolites, essentially [[carbon]], [[nitrogen]], [[oxygen]], and [[sulfur]]. In its adult phase, ''R. pachyptila'' lacks a digestive system. To provide its energetic needs, it retains those dissolved inorganic nutrients (sulfide, carbon dioxide, oxygen, nitrogen) into its plume and transports them through a vascular system to the [[trophosome]], which is suspended in paired coelomic cavities and is where the intracellular symbiotic bacteria are found.<ref name = "Stewart_2006" /><ref name="Childress_1993">{{cite journal| vauthors = Childress JJ, Lee RW, Sanders NK, Felbeck H, Oros DR, Toulmond A, Desbruyeres D, Kennicutt II MC, Brooks J |date=1993|title=Inorganic carbon uptake in hydrothermal vent tubeworms facilitated by high environmental ''p''CO<sub>2</sub>|journal=Nature|volume=362|issue=6416|pages=147–149|doi=10.1038/362147a0 |bibcode=1993Natur.362..147C|s2cid=4341949}}</ref><ref name="Childress_1984">{{cite journal| vauthors = Childress JJ, Arp AJ, Fisher CR |date=1984|title=Metabolic and blood characteristics of the hydrothermal vent tube-worm ''Riftia pachyptila''|journal=Marine Biology|volume=83|issue=2|pages=109–124|doi=10.1007/bf00394718|bibcode=1984MarBi..83..109C |s2cid=84806980 }}</ref> The [[trophosome]]<ref name="Robidart_2008">{{cite journal | vauthors = Robidart JC, Bench SR, Feldman RA, Novoradovsky A, Podell SB, Gaasterland T, Allen EE, Felbeck H | display-authors = 6 | title = Metabolic versatility of the ''Riftia pachyptila'' endosymbiont revealed through metagenomics | journal = Environmental Microbiology | volume = 10 | issue = 3 | pages = 727–37 | date = March 2008 | pmid = 18237306 | doi = 10.1111/j.1462-2920.2007.01496.x | bibcode = 2008EnvMi..10..727R }}</ref>  is a soft tissue that runs through almost the whole length of the tube's coelom. It retains a large number of bacteria on the order of 10<sup>9</sup> bacteria per gram of fresh weight.<ref name="Hand_1983">{{cite journal| vauthors = Hand SC, Somero GN |date=August 1983|title=Energy Metabolism Pathways of Hydrothermal Vent Animals: Adaptations to a Food-Rich and Sulfide-Rich Deep-Sea Environment|journal=The Biological Bulletin |volume=165|issue=1|pages=167–181 |doi=10.2307/1541362 |jstor=1541362|url=https://www.biodiversitylibrary.org/part/33940|name-list-style=vanc}}</ref> Bacteria in the trophosome are retained inside bacteriocytes, thereby having no contact with the external environment. Thus, they rely on ''R. pachyptila'' for the assimilation of nutrients needed for the array of metabolic reactions they employ and for the excretion of waste products of [[Biological carbon fixation|carbon fixation]] pathways. At the same time, the tube worm depends completely on the microorganisms for the byproducts of their carbon fixation cycles that are needed for its growth.

Initial evidence for a chemoautotrophic symbiosis in ''R. pachyptila'' came from [[Microscopic scale|microscopic]] and [[Biomolecule|biochemical]] analyses showing Gram-negative bacteria packed within a highly vascularized organ in the tubeworm trunk called the [[trophosome]].<ref name="Cavanaugh_1981" /> Additional analyses involving [[stable isotope analysis| stable isotope]],<ref>{{cite journal | vauthors = Rau GH | title = Hydrothermal Vent Clam and Tube Worm 13C/12C: Further Evidence of Nonphotosynthetic Food Sources | journal = Science | volume = 213 | issue = 4505 | pages = 338–40 | date = July 1981 | pmid = 17819906 | doi = 10.1126/science.213.4505.338 | bibcode = 1981Sci...213..338R }}</ref> [[Enzyme|enzymatic]],<ref>{{cite journal | vauthors = Renosto F, Martin RL, Borrell JL, Nelson DC, Segel IH | title = ATP sulfurylase from trophosome tissue of Riftia pachyptila (hydrothermal vent tube worm) | journal = Archives of Biochemistry and Biophysics | volume = 290 | issue = 1 | pages = 66–78 | date = October 1991 | pmid = 1898101 | doi = 10.1016/0003-9861(91)90592-7 }}</ref><ref name="Felbeck_1981" /> and [[physiological]]<ref>{{cite book |last=Fisher |first=Charles R. | name-list-style = vanc |chapter=Toward an Appreciation of Hydrothennal-Vent Animals: Their Environment, Physiological Ecology, and Tissue Stable Isotope Values|date=1995|pages=297–316|publisher=American Geophysical Union|isbn=978-1-118-66399-8 |doi=10.1029/gm091p0297 |title=Seafloor Hydrothermal Systems: Physical, Chemical, Biological, and Geological Interactions|series=Geophysical Monograph Series}}</ref> characterizations confirmed that the end symbionts of ''R. pachyptila'' oxidize reduced-sulfur compounds to synthesize ATP for use in [[autotroph]]ic carbon fixation through the [[Calvin cycle]]. The host tubeworm enables the uptake and transport of the substrates required for thioautotrophy, which are HS<sup>−</sup>, O<sub>2</sub>, and CO<sub>2</sub>, receiving back a portion of the organic matter synthesized by the  symbiont population. The adult tubeworm,  given its inability to feed on particulate matter and its entire dependency on its symbionts for nutrition, the bacterial population is then the primary source of carbon acquisition for the symbiosis. Discovery of bacterial–invertebrate chemoautotrophic symbioses, initially in vestimentiferan tubeworms<ref name="Cavanaugh_1981" /><ref name="Felbeck_1981" /> and then in [[Vesicomyidae|vesicomyid]] clams and [[Mytilidae|mytilid]] mussels,<ref name="Felbeck_1981" /> pointed to an even more remarkable source of nutrition sustaining the invertebrates at [[Hydrothermal vent|vents]].

== Endosymbiosis with chemoautotrophic bacteria ==
A wide range of bacterial diversity is associated with symbiotic relationships with ''R. pachyptila''. Many bacteria belong to the phylum [[Campylobacterota]] (formerly class Epsilonproteobacteria)<ref name="López-García_2002">{{cite journal | vauthors = López-García P, Gaill F, Moreira D | title = Wide bacterial diversity associated with tubes of the vent worm ''Riftia pachyptila'' | journal = Environmental Microbiology | volume = 4 | issue = 4 | pages = 204–15 | date = April 2002 | pmid = 12010127 | doi = 10.1046/j.1462-2920.2002.00286.x | bibcode = 2002EnvMi...4..204L | s2cid = 3940740 }}</ref> as supported by the recent discovery in 2016 of the new species ''Sulfurovum riftiae'' belonging to the phylum Campylobacterota, family Helicobacteraceae isolated from ''R. pachyptila'' collected from the [[East Pacific Rise]].<ref name="Sulfurovum riftiae sp. nov., a meso">{{cite journal | vauthors = Giovannelli D, Chung M, Staley J, Starovoytov V, Le Bris N, Vetriani C | title = ''Sulfurovum riftiae'' sp. nov., a mesophilic, thiosulfate-oxidizing, nitrate-reducing chemolithoautotrophic epsilonproteobacterium isolated from the tube of the deep-sea hydrothermal vent polychaete ''Riftia pachyptila'' | journal = International Journal of Systematic and Evolutionary Microbiology | volume = 66 | issue = 7 | pages = 2697–2701 | date = July 2016 | pmid = 27116914 | doi = 10.1099/ijsem.0.001106 | doi-access = free }}</ref> Other symbionts belong to the class [[Deltaproteobacteria|Delta]]-, [[Alphaproteobacteria|Alpha]]- and [[Gammaproteobacteria]].<ref name="López-García_2002" /> The ''Candidatus'' Endoriftia persephone (Gammaproteobacteria) is a facultative ''R. pachyptila'' symbiont and has been shown to be a [[mixotroph]], thereby exploiting both [[Calvin cycle|Calvin Benson cycle]] and [[Reverse Krebs cycle|reverse TCA cycle]] (with an unusual [[ATP citrate lyase]]) according to availability of carbon resources and whether it is free living in the environment or inside a [[Eukaryote|eukaryotic]] host. The bacteria apparently prefer a [[heterotroph]]ic lifestyle when carbon sources are available.<ref name="Robidart_2008" />

Evidence based on [[16S ribosomal RNA|16S rRNA]] analysis affirms that ''R. pachyptila'' chemoautotrophic bacteria belong to two different clades: [[Gammaproteobacteria]]<ref>{{cite journal | vauthors = Distel DL, Lane DJ, Olsen GJ, Giovannoni SJ, Pace B, Pace NR, Stahl DA, Felbeck H | display-authors = 6 | title = Sulfur-oxidizing bacterial endosymbionts: Analysis of phylogeny and specificity by 16S rRNA sequences | journal = Journal of Bacteriology | volume = 170 | issue = 6 | pages = 2506–10 | date = June 1988 | pmid = 3286609 | pmc = 211163 | doi = 10.1128/jb.170.6.2506-2510.1988 }}</ref><ref name = "Stewart_2006" /> and [[Campylobacterota]] (e.g. ''Sulfurovum riftiae'')<ref name="Sulfurovum riftiae sp. nov., a meso"/> that get energy from the [[Redox|oxidation]] of inorganic sulfur compounds such as [[hydrogen sulfide]] (H<sub>2</sub>S, HS<sup>−</sup>, S<sup>2-</sup>) to synthesize [[Adenosine triphosphate|ATP]] for [[Biological carbon fixation|carbon fixation]] via the [[Calvin cycle]].<ref name = "Stewart_2006" /> Unfortunately, most of these bacteria are still uncultivable. Symbiosis works so that ''R. pachyptila'' provides nutrients such as HS<sup>−</sup>, O<sub>2</sub>, CO<sub>2</sub> to bacteria, and in turn it receives organic matter from them. Thus, because of lack of a digestive system, ''R. pachyptila'' depends entirely on its bacterial symbiont  to survive.<ref>{{cite journal | vauthors = Fisher CR |title=Toward an appreciation of hydrothennal-vent animals: Their environment, physiological ecology, and tissue stable isotope values|journal = Washington DC American Geophysical Union Geophysical Monograph Series|volume = 91|pages = 297–316 |bibcode = 1995GMS....91..297F|year = 1995|doi = 10.1029/GM091p0297|series = Geophysical Monograph Series|isbn = 9781118663998}}</ref><ref>{{cite journal | vauthors = Nelson DC |url=https://ci.nii.ac.jp/naid/10015431283/|title=Chemoautotrophic and methanotrophic endosymbiotic bacteria at deep-sea vents and seeps|journal=The Microbiology of Deep-Sea Hydrothermal Vents |year=1995}}</ref>

In the first step of sulfide-oxidation, reduced sulfur (HS<sup>−</sup>) passes from the external environment into ''R. pachyptila'' blood, where, together with O<sub>2</sub>, it is bound by hemoglobin, forming the complex Hb-O<sub>2</sub>-HS<sup>−</sup> and then it is transported to the trophosome, where bacterial symbionts reside. Here, HS<sup>−</sup> is oxidized to elemental sulfur (S<sup>0</sup>) or to [[sulfite]] (SO<sub>3</sub><sup>2-</sup>).<ref name = "Stewart_2006" />

In the second step, the symbionts make sulfite-oxidation by the "APS pathway", to get ATP. In this biochemical pathway, AMP reacts with sulfite in the presence of the [[enzyme]] APS reductase, giving APS (adenosine 5'-phosphosulfate). Then, APS reacts with the enzyme ATP sulfurylase in presence of [[pyrophosphate]] (PPi) giving ATP ([[substrate-level phosphorylation]]) and sulfate (SO<sub>4</sub><sup>2-</sup>) as end products.<ref name = "Stewart_2006" /> In formulas:

* <chem>AMP + SO3^2- ->[APSreductase] APS</chem>
* <chem>APS  +  PPi  ->[ATP sulfurylase] ATP + SO4^2-</chem>

The electrons released during the entire sulfide-oxidation process enter in an electron transport chain, yielding a proton gradient that produces ATP ([[oxidative phosphorylation]]). Thus, ATP generated from oxidative phosphorylation and ATP produced by substrate-level phosphorylation become available for CO<sub>2</sub> fixation in Calvin cycle, whose presence has been demonstrated by the presence of two key enzymes of this pathway: [[phosphoribulokinase]] and [[RuBisCO|RubisCO]].<ref name="Felbeck_1981" /><ref>{{cite journal | vauthors = Robinson JJ, Stein JL, Cavanaugh CM | title = Cloning and sequencing of a form II ribulose-1,5-biphosphate carboxylase/oxygenase from the bacterial symbiont of the hydrothermal vent tubeworm ''Riftia pachyptila'' | journal = Journal of Bacteriology | volume = 180 | issue = 6 | pages = 1596–9 | date = March 1998 | doi = 10.1128/JB.180.6.1596-1599.1998 | pmid = 9515935 | pmc = 107066 }}</ref>

To support this unusual metabolism, ''R. pachyptila'' has to absorb all the substances necessary for both sulfide-oxidation and carbon fixation, that is: HS<sup>−</sup>, O<sub>2</sub> and CO<sub>2</sub> and other fundamental bacterial nutrients such as N and P. This means that the tubeworm must be able to access both oxic and anoxic areas.

Oxidation of [[Redox|reduced]] sulfur compounds requires the presence of oxidized reagents such as [[oxygen]] and [[nitrate]]. Hydrothermal vents are characterized by conditions of high [[Hypoxia (environmental)|hypoxia]]. In hypoxic conditions, [[sulfur]]-storing organisms start producing [[hydrogen sulfide]]. Therefore, the production of in [[Hydrogen sulfide|H<sub>2</sub>S]] in [[Hypoxia (environmental)|anaerobic]] conditions is common among thiotrophic symbiosis. H<sub>2</sub>S can be damaging for some [[Physiology|physiological]] processes as it inhibits the activity of [[cytochrome c oxidase]], consequentially impairing [[oxidative phosphorylation]]. In ''R. pachyptila'' the production of hydrogen sulfide starts after 24h of hypoxia. In order to avoid physiological damage some animals, including ''Riftia'' ''pachyptila'' are able to bind H<sub>2</sub>S to [[Hemoglobin|haemoglobin]] in the blood to eventually expel it in the surrounding [[Biophysical environment|environment]].

== Carbon fixation and organic carbon assimilation ==
Unlike [[Animal|metazoans]], which respire carbon dioxide as a waste product, ''R. pachyptila''-symbiont association has a demand for a net uptake of CO<sub>2</sub> instead, as a [[cnidaria]]n-symbiont associations.<ref name="Van_Dover_2004">{{cite journal |last1=Van Dover |first1=Cindy Lee |last2=Lutz |first2=Richard A | name-list-style = vanc |date=2004 |title=Experimental ecology at deep-sea hydrothermal vents: a perspective |journal=Journal of Experimental Marine Biology and Ecology |volume=300 |issue=1–2 |pages=273–307 |doi=10.1016/j.jembe.2003.12.024 |bibcode=2004JEMBE.300..273V }}</ref>
<!-- Deleted image removed: [[File:Metabolism in the symbiosis between Riftia pachyptila and a chemosynthetic sulfur-oxidizing bacterium.jpeg|alt=Stewart, F. J., & Cavanaugh, C. M. (2005)|thumb|upright=1.35|Proposed model of metabolism in the symbiosis between ''Riftia pachyptila'' and a chemosynthetic sulfur-oxidizing bacterium.]] -->
Ambient deep-sea water contains an abundant amount of inorganic carbon in the form of [[bicarbonate]] HCO<sub>3</sub><sup>−</sup>, but it is actually the chargeless form of inorganic carbon, CO<sub>2</sub>, that is easily diffusible across membranes. The low partial pressures of CO<sub>2</sub> in the deep-sea environment is due to the seawater [[alkali]]ne pH and the high solubility of CO<sub>2</sub>, yet the pCO<sub>2</sub> of the blood of ''R. pachyptila'' may be as much as two orders of magnitude greater than the pCO<sub>2</sub> of deep-sea water.<ref name="Van_Dover_2004" />

CO<sub>2</sub> partial pressures are transferred to the vicinity of vent fluids due to the enriched inorganic carbon content of vent fluids and their lower pH.<ref name = "Stewart_2006" /> CO<sub>2</sub> uptake in the worm is enhanced by the higher [[pH]] of its blood (7.3–7.4), which favors the [[bicarbonate ion]] and thus promotes a steep gradient across which CO<sub>2</sub> diffuses into the vascular blood of the plume.<ref>{{cite journal| vauthors = Goffredi SK, Childress JJ |date=2001|title=Activity and inhibitor sensitivity of ATPases in the hydrothermal vent tubeworm ''Riftia pachyptila'': a comparative approach|journal=Marine Biology|volume=138|issue=2|pages=259–265|doi=10.1007/s002270000462|bibcode=2001MarBi.138..259G |s2cid=83539580 }}</ref><ref name="Stewart_2006" /> The facilitation of CO<sub>2</sub> uptake by high environmental pCO<sub>2</sub> was first inferred based on measures of elevated blood and coelomic fluid pCO<sub>2</sub> in tubeworms, and was subsequently demonstrated through incubations of intact animals under various pCO<sub>2</sub> conditions.<ref name="Childress_1984" />

Once CO<sub>2</sub> is fixed by the [[Symbiosis|symbionts]], it must be assimilated by the host tissues. The supply of fixed carbon to the host is  transported via organic molecules from the trophosome in the [[hemolymph]], but the relative importance of translocation and symbiont digestion is not yet known.<ref name="Childress_1984" /><ref name="Bright_2000">{{cite journal| vauthors = Bright M, Keckeis H, Fisher CR |date=2000-05-19|title=An autoradiographic examination of carbon fixation, transfer and utilization in the ''Riftia pachyptila'' symbiosis|journal=Marine Biology|volume=136|issue=4|pages=621–632|doi=10.1007/s002270050722|bibcode=2000MarBi.136..621B |s2cid=84235858 }}</ref> Studies proved that within 15 min, the label first appears in symbiont-free host tissues, and that indicates a significant amount of release of organic carbon immediately after fixation. After 24 h, labeled carbon is clearly evident in the epidermal tissues of the body wall. Results of the pulse-chase [[autoradiograph]]ic experiments  were also evident with ultrastructural evidence for digestion of symbionts in the peripheral regions of the trophosome lobules.<ref name="Bright_2000" /><ref>{{cite journal| vauthors = Bright M, Sorgo A |date=2005-05-11|title=Ultrastructural reinvestigation of the trophosome in adults of ''Riftia pachyptila'' (Annelida, Siboglinidae)|journal=Invertebrate Biology|volume=122|issue=4|pages=347–368|doi=10.1111/j.1744-7410.2003.tb00099.x }}</ref>

== Sulfide acquisition ==
In deep-sea hydrothermal vents, [[sulfide]] and [[oxygen]] are present in different areas. Indeed, the [[reducing agent|reducing]] fluid of hydrothermal vents is rich in sulfide, but poor in oxygen, whereas sea water is richer in dissolved oxygen. Moreover, sulfide is immediately oxidized by dissolved oxygen to form partly, or totally, oxidized sulfur compounds like [[thiosulfate]] (S<sub>2</sub>O<sub>3</sub><sup>2-</sup>)  and ultimately  [[sulfate]] (SO<sub>4</sub><sup>2-</sup>), respectively less, or no longer, usable for microbial oxidation metabolism.<ref>{{cite journal |vauthors=Zhang JZ, Millero FJ |year=1993 |title=The products from the oxidation of H<sub>2</sub>S in seawater |journal=Geochimica et Cosmochimica Acta |volume=57 |issue=8 |pages=1705–1718 |doi=10.1016/0016-7037(93)90108-9 |doi-access=free |bibcode=1993GeCoA..57.1705Z}}</ref> This causes the substrates to be less available for microbial activity, thus bacteria are constricted to compete with oxygen to get their nutrients. In order to avoid this issue, several microbes have evolved to make [[symbiosis]] with [[eukaryote|eukaryotic]] hosts.<ref>{{cite journal |vauthors=Cavanaugh CM |title=Symbioses of chemoautotrophic bacteria and marine invertebrates from hydrothermal vents and reducing sediments |journal=Bulletin of the Biological Society of Washington |date=1985 |volume=6 |pages=373–388 |url=https://ci.nii.ac.jp/naid/10003540266/}}</ref><ref name="Stewart_2006"/> In fact, ''R. pachyptila'' is able to cover the [[aerobic organism|oxic]] and [[anoxic waters|anoxic]] areas  to get both sulfide and oxygen<ref>{{cite journal |vauthors=Cavanaugh CM |title=Microbial symbiosis: patterns of diversity in the marine environment |journal=American Zoologist |date=February 1994 |volume=34 |issue=1 |pages=79–89 |doi=10.1093/icb/34.1.79 |doi-access=free}}</ref><ref>{{cite book |vauthors=Fisher CR |date=1996 |title=Ecophysiology of primary production at deep-sea vents and seeps |url=https://www.zobodat.at/pdf/BioEco_11_0313-0336.pdf}}</ref><ref>{{cite journal |vauthors=Polz MF, Ott JA, Bregut M, Cavanaugh CM |title=When Bacteria Hitch a Ride |journal=ASM News-American Society for Microbiology |date=2000 |volume=66 |issue=9 |pages=531–539}}</ref> thanks to its [[hemoglobin]] that can bind sulfide reversibly and apart from oxygen by functional binding sites determined to be zinc ions embedded in the A2 chains of the hemoglobins.<ref>{{Cite journal |last1=Flores |first1=Jason F. |last2=Fisher |first2=Charles R. |last3=Carney |first3=Susan L. |last4=Green |first4=Brian N. |last5=Freytag |first5=John K. |last6=Schaeffer |first6=Stephen W. |last7=Royer |first7=William E. |date=2005-02-22 |title=Sulfide binding is mediated by zinc ions discovered in the crystal structure of a hydrothermal vent tubeworm hemoglobin |journal=Proceedings of the National Academy of Sciences |language=en |volume=102 |issue=8 |pages=2713–2718 |doi=10.1073/pnas.0407455102 |doi-access=free |issn=0027-8424 |pmc=549462 |pmid=15710902|bibcode=2005PNAS..102.2713F }}</ref><ref>{{Cite journal |last1=Flores |first1=Jason F. |last2=Hourdez |first2=téphane M. |date=2006 |title=The zinc-mediated sulfide-binding mechanism of hydrothermal vent tubeworm 400-kDa hemoglobin |journal=Cahiers de Biologie Marine (CBM) |volume=47 |issue= |pages=371–377 |doi=10.21411/cbm.a.11ae33dc}}</ref><ref>{{Cite journal |last1=Royer |first1=William E. |last2=Zhu |first2=Hao |last3=Gorr |first3=Thomas A. |last4=Flores |first4=Jason F. |last5=Knapp |first5=James E. |date=2005 |title=Allosteric Hemoglobin Assembly: Diversity and Similarity |journal=Journal of Biological Chemistry |volume=280 |issue=30 |pages=27477–27480 |doi=10.1074/jbc.r500006200 |issn=0021-9258 |doi-access=free |pmid=15932877 }}</ref> and then transport it to the [[trophosome]], where bacterial metabolism can occur. It has also been suggested that [[cysteine]] residues are involved in this process.<ref>{{cite journal |vauthors=Zal F, Suzuki T, Kawasaki Y, Childress JJ, Lallier FH, Toulmond A |title=Primary structure of the common polypeptide chain b from the multi-hemoglobin system of the hydrothermal vent tube worm ''Riftia pachyptila'': an insight on the sulfide binding-site |journal=Proteins |volume=29 |issue=4 |pages=562–574 |date=December 1997 |pmid=9408952 |doi=10.1002/(SICI)1097-0134(199712)29:4<562::AID-PROT15>3.0.CO;2-K |s2cid=25706128}}</ref><ref>{{cite journal |vauthors=Zal F, Leize E, Lallier FH, Toulmond A, Van Dorsselaer A, Childress JJ |title=S-Sulfohemoglobin and disulfide exchange: the mechanisms of sulfide binding by ''Riftia pachyptila'' hemoglobins |journal=Proceedings of the National Academy of Sciences of the United States of America |volume=95 |issue=15 |pages=8997–9002 |date=July 1998 |pmid=9671793 |pmc=21191 |doi=10.1073/pnas.95.15.8997 |bibcode=1998PNAS...95.8997Z |doi-access=free }}</ref><ref>{{cite journal |vauthors=Bailly X, Jollivet D, Vanin S, Deutsch J, Zal F, Lallier F, Toulmond A |title=Evolution of the sulfide-binding function within the globin multigenic family of the deep-sea hydrothermal vent tubeworm ''Riftia pachyptila'' |journal=Molecular Biology and Evolution |volume=19 |issue=9 |pages=1421–133 |date=September 2002 |pmid=12200470 |doi=10.1093/oxfordjournals.molbev.a004205 }}</ref>

== Symbiont acquisition ==
The acquisition of a symbiont by a host can occur in these ways:

*'''Environmental transfer''' (symbiont acquired from a free-living population in the environment)
* '''Vertical transfer''' (parents transfer symbiont to offspring via eggs)
* '''Horizontal transfer''' (hosts that share the same environment)

Evidence suggests that ''R. pachyptila'' acquires its symbionts through its environment. In fact, [[16S ribosomal RNA|16S rRNA]] gene analysis showed that vestimentiferan tubeworms belonging to three different genera: ''Riftia'', ''Oasisia'', and ''Tevnia'', share the same bacterial symbiont [[phylotype]].<ref>{{cite journal | vauthors = Feldman RA, Black MB, Cary CS, Lutz RA, Vrijenhoek RC | title = Molecular phylogenetics of bacterial endosymbionts and their vestimentiferan hosts | journal = Molecular Marine Biology and Biotechnology | volume = 6 | issue = 3 | pages = 268–77 | date = September 1997 | pmid = 9284565 | url = https://www.researchgate.net/publication/13935526 }}</ref><ref>{{cite journal | vauthors = Laue BE, Nelson DC | title = Sulfur-oxidizing symbionts have not co-evolved with their hydrothermal vent tube worm hosts: an RFLP analysis | journal = Molecular Marine Biology and Biotechnology | volume = 6 | issue = 3 | pages = 180–8 | date = September 1997 | pmid = 9284558 }}</ref><ref>{{cite journal | vauthors = Di Meo CA, Wilbur AE, Holben WE, Feldman RA, Vrijenhoek RC, Cary SC | title = Genetic variation among endosymbionts of widely distributed vestimentiferan tubeworms | journal = Applied and Environmental Microbiology | volume = 66 | issue = 2 | pages = 651–8 | date = February 2000 | pmid = 10653731 | pmc = 91876 | doi = 10.1128/AEM.66.2.651-658.2000 | bibcode = 2000ApEnM..66..651D }}</ref><ref>{{cite journal | vauthors = Nelson K, Fisher CR |url=https://pennstate.pure.elsevier.com/en/publications/absence-of-cospeciation-in-deep-sea-vestimentiferan-tube-worms-an|title=Absence of cospeciation in deep-sea vestimentiferan tube worms and their bacterial endosymbionts|journal=Symbiosis|volume=28|issue=1|pages=1–15 |year=2000}}</ref><ref>{{cite journal |vauthors=McMullin ER, Hourdez ST, Schaeffer SW, Fisher CR |year=2003 |url=http://scripts.cac.psu.edu/users/s/w/sws4/Pubs/26.pdf |archive-url=https://web.archive.org/web/20191216194249/http://scripts.cac.psu.edu/users/s/w/sws4/Pubs/26.pdf |url-status=dead |archive-date=December 16, 2019 |title=Phylogeny and Biogeography of Deep Sea Vestimentiferan Tubeworms and Their Bacterial Symbionts |journal=Symbiosis |volume=34 |pages=1–41 }}</ref>

This proves that ''R. pachyptila'' takes its symbionts from a free-living bacterial population in the environment. Other studies also support this thesis, because analyzing ''R. pachyptila'' eggs, 16S rRNA belonging to the symbiont was not found, showing that the bacterial symbiont is not transmitted by vertical transfer.<ref>{{cite journal | vauthors = Cary SC, Warren W, Anderson E, Giovannoni SJ | title = Identification and localization of bacterial endosymbionts in hydrothermal vent taxa with symbiont-specific polymerase chain reaction amplification and in situ hybridization techniques | journal = Molecular Marine Biology and Biotechnology | volume = 2 | issue = 1 | pages = 51–62 | date = February 1993 | pmid = 8364689 }}</ref>

Another proof to support the environmental transfer comes from several studies conducted in the late 1990s.<ref>{{cite journal | vauthors = Millikan DS, Felbeck H, Stein JL | title = Identification and characterization of a flagellin gene from the endosymbiont of the hydrothermal vent tubeworm Riftia pachyptila | journal = Applied and Environmental Microbiology | volume = 65 | issue = 7 | pages = 3129–33 | date = July 1999 | pmid = 10388713 | pmc = 91466 | doi = 10.1128/AEM.65.7.3129-3133.1999 | bibcode = 1999ApEnM..65.3129M }}</ref> PCR was used to detect and identify a ''R. pachyptila'' symbiont gene whose sequence was very similar to the ''fliC'' gene that encodes some primary protein subunits ([[flagellin]]) required for [[flagellum]] synthesis. Analysis showed that ''R. pachyptila'' symbiont has at least one gene needed for flagellum synthesis. Hence, the question arose as to the purpose of the flagellum. Flagellar motility would be useless for a bacterial symbiont transmitted vertically, but if the symbiont came from the external environment, then a flagellum would be essential to reach the host organism and to colonize it. Indeed, several symbionts use this method to colonize eukaryotic hosts.<ref>{{cite journal | vauthors = Chua KL, Chan YY, Gan YH | title = Flagella are virulence determinants of ''Burkholderia pseudomallei'' | journal = Infection and Immunity | volume = 71 | issue = 4 | pages = 1622–9 | date = April 2003 | pmid = 12654773 | pmc = 152022 | doi = 10.1128/IAI.71.4.1622-1629.2003 }}</ref><ref>{{cite journal | vauthors = Gavín R, Merino S, Altarriba M, Canals R, Shaw JG, Tomás JM | title = Lateral flagella are required for increased cell adherence, invasion and biofilm formation by Aeromonas spp | journal = FEMS Microbiology Letters | volume = 224 | issue = 1 | pages = 77–83 | date = July 2003 | pmid = 12855171 | doi = 10.1016/S0378-1097(03)00418-X | doi-access = free }}</ref><ref>{{cite journal | vauthors = Kirov SM | title = Bacteria that express lateral flagella enable dissection of the multifunctional roles of flagella in pathogenesis | journal = FEMS Microbiology Letters | volume = 224 | issue = 2 | pages = 151–9 | date = July 2003 | pmid = 12892877 | doi = 10.1016/S0378-1097(03)00445-2 | doi-access = free }}</ref><ref>{{cite journal | vauthors = Dons L, Eriksson E, Jin Y, Rottenberg ME, Kristensson K, Larsen CN, Bresciani J, Olsen JE | display-authors = 6 | title = Role of flagellin and the two-component CheA/CheY system of Listeria monocytogenes in host cell invasion and virulence | journal = Infection and Immunity | volume = 72 | issue = 6 | pages = 3237–44 | date = June 2004 | pmid = 15155625 | pmc = 415653 | doi = 10.1128/IAI.72.6.3237-3244.2004 }}</ref>

Thus, these results confirm the environmental transfer of ''R. pachyptila'' symbiont.

== Reproduction ==
''R. pachyptila''<ref>{{cite journal | vauthors = Jones ML | title = Riftia pachyptila Jones: Observations on the Vestimentiferan Worm from the Galapagos Rift | journal = Science | volume = 213 | issue = 4505 | pages = 333–6 | date = July 1981 | pmid = 17819904 | doi = 10.1126/science.213.4505.333 | bibcode = 1981Sci...213..333J }}</ref> is a [[dioecious]] vestimentiferan.<ref>{{cite journal| vauthors = Karaseva NP, Rimskaya-Korsakova NN, Galkin SV, Malakhov VV |date= December 2016 |title=Taxonomy, geographical and bathymetric distribution of vestimentiferan tubeworms (Annelida, Siboglinidae)|journal=Biology Bulletin|language=en|volume=43|issue=9|pages=937–969|doi=10.1134/S1062359016090132|bibcode= 2016BioBu..43..937K |s2cid= 16005133 }}</ref> Individuals of this species are [[sessility (motility)|sessile]] and are found clustered together around deep-sea hydrothermal vents of the East Pacific Rise and the Galapagos Rift.<ref name="Coykendall_2011"/> The size of a patch of individuals surrounding a vent is within the scale of tens of metres.<ref>{{cite journal| vauthors = Cary SC, Felbeck H, Holland ND |date=1989|title=Observations on the reproductive biology of the hydrothermal vent tube worm ''Riftia pachyptila''|journal=Marine Ecology Progress Series|language=en|volume=52|pages=89–94|doi=10.3354/meps052089 |bibcode=1989MEPS...52...89C|doi-access=free}}</ref>

The male's [[Spermatozoon|spermatozoa]] are thread-shaped and are composed of three distinct regions: the [[acrosome]] (6 μm), the nucleus (26 μm) and the tail (98 μm). Thus, the single spermatozoa is about 130 μm long overall, with a diameter of 0.7 μm, which becomes narrower near the tail area, reaching 0.2 μm. The sperm is arranged into an agglomeration of around 340–350 individual spermatozoa that create a torch-like shape. The cup part is made up of acrosomes and nucleus, while the handle is made up by the tails. The spermatozoa in the package are held together by [[fibril]]s. Fibrils also coat the package itself to ensure cohesion.{{citation needed|date=December 2019}}

The large [[Ovary|ovaries]] of females run within the gonocoel along the entire length of the trunk and are ventral to the trophosome. Eggs at different maturation stages can be found in the middle area of the ovaries, and depending on their developmental stage, are referred to as: [[Oogonium|oogonia]], [[oocyte]]s, and [[Granulosa cell|follicular cells]]. When the oocytes mature, they acquire [[protein]] and [[lipid]] yolk granules.{{citation needed|date=December 2019}}

Males release their sperm into sea water. While the released agglomerations of spermatozoa, referred to as spermatozeugmata, do not remain intact for more than 30 seconds in laboratory conditions, they may maintain integrity for longer periods of time in specific hydrothermal vent conditions. Usually, the spermatozeugmata swim into the female's tube. Movement of the cluster is conferred by the collective action of each spermatozoon moving independently. Reproduction has also been observed involving only a single spermatozoon reaching the female's tube. Generally, [[Fertilisation|fertilization]] in ''R. pachyptila'' is considered internal. However, some argue that, as the sperm is released into sea water and only afterwards reaches the eggs in the [[oviduct]]s, it should be defined as internal-external.{{citation needed|date=December 2019}}

''R. pachyptila'' is completely dependent on the production of [[volcanic gas]]es and the presence of [[sulfide]]-oxidizing bacteria. Therefore, its [[metapopulation]] distribution is profoundly linked to volcanic and [[Tectonics|tectonic]] activity that create active hydrothermal vent sites with a patchy and [[Ephemerality|ephemeral]] distribution. The distance between active sites along a rift or adjacent segments can be very high, reaching hundreds of km.<ref name="Coykendall_2011">{{cite journal | vauthors = Coykendall DK, Johnson SB, Karl SA, Lutz RA, Vrijenhoek RC | title = Genetic diversity and demographic instability in ''Riftia pachyptila'' tubeworms from eastern Pacific hydrothermal vents | journal = BMC Evolutionary Biology | volume = 11 | issue = 1 | pages = 96 | date = April 2011 | pmid = 21489281 | pmc = 3100261 | doi = 10.1186/1471-2148-11-96 | doi-access = free | bibcode = 2011BMCEE..11...96C }}</ref> This raises the question regarding [[larva]]l [[Biological dispersal|dispersal]]. ''R. pachytpila'' is capable of larval dispersal across distances of 100 to 200&nbsp;km<ref name="Coykendall_2011" /> and cultured larvae show to be viable for 38 days.<ref>{{cite journal | vauthors = Marsh AG, Mullineaux LS, Young CM, Manahan DT | title = Larval dispersal potential of the tubeworm ''Riftia pachyptila'' at deep-sea hydrothermal vents | journal = Nature | volume = 411 | issue = 6833 | pages = 77–80 | date = May 2001 | pmid = 11333980 | doi = 10.1038/35075063 | bibcode = 2001Natur.411...77M | s2cid = 411076 }}</ref> Though dispersal is considered to be effective, the [[genetic variability]] observed in ''R. pachyptila'' metapopulation is low compared to other vent species. This may be due to high [[extinction]] events and [[colonization (biology)|colonization]] events, as ''R. pachyptila'' is one of the first species to colonize a new active site.<ref name="Coykendall_2011" />

The [[endosymbiont]]s of ''R. pachyptila'' are not passed to the fertilized eggs during [[Spawn (biology)|spawning]], but are acquired later during the larval stage of the vestimentiferan worm. ''R. pachyptila'' [[plankton]]ic larvae that are transported through sea-bottom currents until they reach active hydrothermal vents sites, are referred to as trophocores. The trophocore stage lacks endosymbionts, which are acquired once larvae settle in a suitable environment and substrate. Free-living bacteria found in the water column are ingested randomly and enter the worm through a [[Cilium|ciliated]] opening of the branchial plume. This opening is connected to the trophosome through a duct that passes through the brain. Once the bacteria are in the gut, the ones that are beneficial to the individual, namely sulfide- oxidizing strains are [[Phagocytosis|phaghocytized]] by [[Epithelium|epithelial]] cells found in the midgut are then retained. Bacteria that do not represent possible endosymbionts are digested. This raises questions as to how ''R. pachyptila'' manages to discern between essential and nonessential bacterial strains. The worm's ability to recognise a beneficial strain, as well as preferential [[Host (biology)|host-specific]] infection by bacteria have been both suggested as being the drivers of this phenomenon.<ref name="Jones 1989"/>

==Growth rate and age==
''R. pachyptila'' has the fastest growth rate of any known marine invertebrate. These organisms have been known to colonize a new site, grow to sexual maturity, and increase in length to 4.9 feet (1.5 m) in less than two years.<ref name="Lutz_1994">{{cite journal | vauthors = Lutz RA, Shank TM, Fornari DJ, Haymon RM, Lilley MD, Von Damm KL, Desbruyeres D | doi = 10.1038/371663a0 | title = Rapid growth at deep-sea vents | journal = Nature | volume = 371 | issue = 6499 | pages = 663–664 | year = 1994 | bibcode = 1994Natur.371..663L | s2cid = 4357672 }}</ref>

Because of the peculiar environment in which ''R. pachyptila'' thrives, this [[species]] differs greatly from other [[Deep sea|deep-sea]] species that do not inhabit hydrothermal vents sites; the activity of diagnostic enzymes for [[glycolysis]], [[citric acid cycle]] and [[Electron transport chain|transport of electrons]] in the tissues of ''R. pachyptila'' is very similar to the activity of these enzymes in the tissues of shallow-living animals. This contrasts with the fact that deep-sea species usually show very low [[Basal metabolic rate|metabolic rates]], which in turn suggests that low water temperature and high pressure in the deep sea do not necessarily limit the metabolic rate of animals and that hydrothermal vents sites display characteristics that are completely different from the surrounding environment, thereby shaping the physiology and biological interactions of the organisms living in these sites.<ref name="Hand_1983" />

<!-- already mentioned  == Curiosity ==

# The association between ''R. pachyptila'' and its symbionts was the first symbiosis described for a marine invertebrate and chemoautotrophic bacteria.<ref name = "Cavanaugh_1981" />
# ''R. pachyptila'' has very high growth rates, in fact it is estimated an increase of up 1.4% of its organic carbon per day.<ref>{{cite journal | vauthors = Childress JJ, Fisher CR, Favuzzi JA, Kochevar RE, Sanders NK, Alayse AM | title = Sulfide-Driven Autotrophic Balance in the Bacterial Symbiont-Containing Hydrothermal Vent Tubeworm, ''Riftia pachyptila'' Jones | journal = The Biological Bulletin | volume = 180 | issue = 1 | pages = 135–153 | date = February 1991 | pmid = 29303639 | doi = 10.2307/1542437 | url = https://archimer.ifremer.fr/doc/00178/28970/27392.pdf | jstor = 1542437 }}</ref><ref name="Lutz_1994" />
 -->

== See also ==
* [[Siboglinidae]]
* ''[[Lamellibrachia]]''
* [[List of long-living organisms]]
* [[Maximum life span]]
* [[Pompeii worm]]
* [[Chemosynthesis]]

== References ==
<references />

== External links ==
{{Commons category|Riftia pachyptila}}
* {{cite web |url=http://animaldiversity.ummz.umich.edu/site/accounts/information/Riftia_pachyptila.html |title=Riftia pachyptila |access-date=February 25, 2008 |last=Privett |first=B. |year=2001 |work=Animal Diversity Web }}
* [http://www.mnh.si.edu/onehundredyears/featured_objects/Riftia.html Giant Tube Worm page at the Smithsonian] {{Webarchive|url=https://web.archive.org/web/20160121223134/http://www.mnh.si.edu/onehundredyears/featured_objects/Riftia.html |date=2016-01-21 }}
* [https://web.archive.org/web/20110720075711/http://education.eol.org/podcast/rifita Podcast on Giant Tube Worm at the Encyclopedia of Life]
* http://www.seasky.org/monsters/sea7a1g.html
* [http://www.ucmp.berkeley.edu/annelida/pogonophora.html Introduction to the Pogonophora: Weird tube worms of the deepest seas]
* https://web.archive.org/web/20090408022512/http://www.ocean.udel.edu/deepsea/level-2/creature/tube.html

{{Extremophile}}
{{Animalia}}

{{Taxonbar|from=Q133020|from2=Q15240740}}

{{DEFAULTSORT:Giant Tube Worm}}
[[Category:Polychaetes]]
<!-- [[Category:Monotypic animal genera]] moved to genus Latin name redirect -->
[[Category:Annelids of the Pacific Ocean]]
[[Category:Animals described in 1981]]
[[Category:Chemosynthetic symbiosis]]
[[Category:Animals living on hydrothermal vents]]