The hyperthermophilic viruses STIV and STIV2 are highly similar structurally and genomically and appear
to be closely related. Cryo-electron microscopy and image reconstruction at a high resolution revealed icosahedral
virions with a triangulation number of T=31. The vertices are decorated with turrets,
which differ in shape in the two viruses and may be
involved in host recognition. Underlying the protein capsid,
a lipid monolayer encasing the circular dsDNA is
found in both viruses.