 According to the comparisons of 16S rRNA genes, "Ignicoccus" represents a new, deeply branching lineage within the family of the Desulfurococcaceae (Huber et al., 2002).Three species are known, "I. islandicus", "I. pacificus" and "I. hospitalis" strain KIN4I.The archaea of the genus "Ignicoccus" have tiny coccoid cells with a diameter of about 2 µm, that exhibit a smooth surface, an outer membrane and no S-layer.