palaeococcus helgesonii palaeococcus helgesonii palaeococcus helgesonii is a hyperthermophillic, anaerobic yet microaerobic archaeon from a geothermal well found in vulcano, italy. it is characterized as sphere-shaped, has a cell diameter ranging from 0.6 to 1.5 μm, a cell envelope consisting of a cytoplasmic membrane, a periplasmic space, a thin, electron-dense layer, and tufts of polar flagella. it occurs singly or in pairs. it can survive in temperatures ranging from 45 to 80°c, a ph range of 5 to 8, and a salt range of 0.5 to 6.0%. in optimal conditions (a temperature of 80°c, a ph around 6.5, and a salt level of 2.8), it has a doubling time of 50 minutes. it also has a g+c of 42.5 mol.%. palaeococcus helgesonii scientific classification domain: archaea kingdom: euryarchaeota phylum: euryarchaeota class: thermococci order: thermococcales family: thermococcaceae genus: palaeococcus species: p. helgesonii binomial name palaeococcus helgesoniiamend et al. 2006