The vents provide a natural ambient temperature in their environment ranging from 2 to 30 °C,[2] and this organism can tolerate extremely high hydrogen sulfide levels.

R. pachyptila was discovered in 1977 on an expedition of the American bathyscaphe DSV Alvin to the Galápagos Rift led by geologist Jack Corliss.

[9][10] 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.

[11] Isolating the vermiform body from white chitinous tube, a small difference exists from the classic three subdivisions typical of phylum Pogonophora:[12] the prosoma, the mesosoma, and the metasoma.

The first body region is the 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).

[15] 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.

[14] 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.

[26] Many studies focusing on this type of symbiosis revealed the presence of chemoautotrophic, endosymbiotic, sulfur-oxidizing bacteria mainly in R. pachyptila,[27] which inhabits extreme environments and is adapted to the particular composition of the mixed volcanic and sea waters.

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.

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 carbon fixation pathways.

Initial evidence for a chemoautotrophic symbiosis in R. pachyptila came from microscopic and biochemical analyses showing Gram-negative bacteria packed within a highly vascularized organ in the tubeworm trunk called the trophosome.

[21] Additional analyses involving stable isotope,[33] enzymatic,[34][26] and physiological[35] characterizations confirmed that the end symbionts of R. pachyptila oxidize reduced-sulfur compounds to synthesize ATP for use in autotrophic carbon fixation through the Calvin cycle.

The host tubeworm enables the uptake and transport of the substrates required for thioautotrophy, which are HS−, O2, and CO2, 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[21][26] and then in vesicomyid clams and mytilid mussels,[26] pointed to an even more remarkable source of nutrition sustaining the invertebrates at vents.

[31] Evidence based on 16S rRNA analysis affirms that R. pachyptila chemoautotrophic bacteria belong to two different clades: Gammaproteobacteria[38][20] and Campylobacterota (e.g. Sulfurovum riftiae)[37] that get energy from the oxidation of inorganic sulfur compounds such as hydrogen sulfide (H2S, HS−, S2-) to synthesize ATP for carbon fixation via the Calvin cycle.

[39][40] In the first step of sulfide-oxidation, reduced sulfur (HS−) passes from the external environment into R. pachyptila blood, where, together with O2, it is bound by hemoglobin, forming the complex Hb-O2-HS− and then it is transported to the trophosome, where bacterial symbionts reside.

[26][41] To support this unusual metabolism, R. pachyptila has to absorb all the substances necessary for both sulfide-oxidation and carbon fixation, that is: HS−, O2 and CO2 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.

In order to avoid physiological damage some animals, including Riftia pachyptila are able to bind H2S to haemoglobin in the blood to eventually expel it in the surrounding environment.

[43][20] The facilitation of CO2 uptake by high environmental pCO2 was first inferred based on measures of elevated blood and coelomic fluid pCO2 in tubeworms, and was subsequently demonstrated through incubations of intact animals under various pCO2 conditions.

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.

[30][44] 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.

In fact, 16S rRNA gene analysis showed that vestimentiferan tubeworms belonging to three different genera: Riftia, Oasisia, and Tevnia, share the same bacterial symbiont phylotype.

[69] Individuals of this species are sessile and are found clustered together around deep-sea hydrothermal vents of the East Pacific Rise and the Galapagos Rift.

Free-living bacteria found in the water column are ingested randomly and enter the worm through a ciliated opening of the branchial plume.

Once the bacteria are in the gut, the ones that are beneficial to the individual, namely sulfide- oxidizing strains are phaghocytized by epithelial cells found in the midgut are then retained.

This contrasts with the fact that deep-sea species usually show very low 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.