Ignicoccus is a genus of hyperthermophillic Archaea living in marine hydrothermal vents.

[1] According to the comparisons of 16S rRNA genes, Ignicoccus represents a new, deeply branching lineage within the family of the Desulfurococcaceae.

[3] 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.

[4] The two layers of membrane previously reported are actually a type of endomembrane system consisting of cytoplasmic protrusions.

In I. hospitalis, these structures harbor the endosymbiotic archaeon Nanoarchaeum equitans.