pyrococcus horikoshii pyrococcus horikoshii pyrococcus horikoshii is a hyperthermophilic, anaerobic archaeon, first isolated from hydrothermal fluid samples obtained at the okinawa trough vents at a depth of 1,395 metres (4,577 ft). it is obligately heterotrophic, cells are irregular cocci with a tuft of flagella, growing optimally at 98 °c, sulphur greatly enhancing its growth. pyrococcus horikoshii scientific classification domain: archaea kingdom: euryarchaeota phylum: euryarchaeota class: thermococci order: thermococcales family: thermococcaceae genus: pyrococcus species: p. horikoshii binomial name pyrococcus horikoshiierauso et al. 1993