Currently, there are four mainstream taxonomic opinions on the classification of the class at the family and order levels. The International Committee on Systematics of Prokaryotes Subcommittee on the Taxonomy of (ICSP), List of Prokaryotic names with Standing in Nomenclature (LPSN) and National Centre for Biotechnology Information (NCBI) adopted taxonomies have three to four orders and up to eight families, while the Genome Taxonomy Database (GTDB) taxonomy proposes only one order with nine families. To resolve the taxonomic inconsistency, phylogenomic analyses based on concatenated single-copy orthologous proteins and 122 concatenated conserved single-copy marker proteins were conducted to infer the taxonomic status of the current representatives of the class at the family and order levels. The current 76 genera with validly published names of the class were able to be assigned into eight families in one order. On the basis of these results, it is proposed that the current species with validly published names of the class should be remerged into the order , then assigned to eight families, , , , , , , and . Thus, fam. nov. is described based on , and and fam. nov. is proposed incorporating and , respectively.