Summary of taxonomy changes ratified by the International Committee on Taxonomy of Viruses (ICTV) from the Archaeal Viruses Subcommittee, 2025

The International Committee on Taxonomy of Viruses (ICTV) holds a ratification vote annually following the review of newly proposed taxa by ICTV Study Groups and members of the virology community. This article reports changes to the taxonomy of viruses infecting archaea that were approved and ratified by the ICTV in March 2025. Six new families of head-tailed viruses expanded the order Caudoviricetes (realm Duplodnaviria ); one new family of filamentous viruses was added to the order Ligamenvirales (realm Adnaviria ); one new family of viruses with pleomorphic virions was included within a new phylum, new order and new class in the kingdom Trapavirae (realm Monodnaviria ); finally, three new families were created for spindle-shaped viruses that remain unassigned to higher level taxa. The 25 new species represent viruses infecting a broad range of archaea, including members of the classes Archaeoglobi, Bathyarchaeia, Methanobacteria, Methanomicrobia, Nitrososphaeria and Poseidoniia. Most of these viruses have been discovered by metagenomics in samples derived from diverse environments, including ambient and extreme marine ecosystems, the gastrointestinal tract of humans and animals, anaerobic digesters and terrestrial hot springs. Following this taxonomic update, archaeal viruses are officially classified into a total of 163 virus species in 94 genera within 62 families.