Girus

A girus (a contraction of giant virus or gigantic virus) is a very large virus. They are giant nucleocytoplasmic large DNA viruses (NCLDVs), having unique genes not found in other life, with separate phylogenic trees for those genes.

While the exact criteria as defined in the scientific literature varies, giruses are generally described as those viruses having large pseudo-icosahedral capsids (200 to 400 nanometers) surrounded by a thick (approximately 100 nm) layer of filamentous protein fibers with large double-stranded DNA genomes (300 to 1000 kilobase pairs or larger) encoding a large contingent of genes (of the order of 1000 genes). While few have been characterized in detail, the most notable examples of giruses are the phylogenetically related megavirus and mimivirus, belonging to the Megaviridae and Mimiviridae families, respectively, having the largest capsid diameters of all known viruses.