As indicated by the ☞ ICNP in Rule 8, names of ☞ classes should be formed by appending -ia to the stem of the name of the type genus of the type order of the class. However, many ☞ validly published names of classes deviate from this scheme. Either other suffixes were used or the name of the class was not derived from the expected stem.
In many cases, the name of the class was formed from the name of the type genus of the type order of the class by converting the last component of that genus name from the nominative singular to the nominative plural. A similar scheme was often used for irregular names that are not derived from a genus name, such as some names ending in -bacteria (plural of bacterium) or in -cutes (plural of cutis). The grammatical gender of such class names varies; it is that of their last component. In yet other cases the feminine plural ending -ae (first declension) was used incorrectly, or even less common endings were used. Orthographically correct plural endings of class names validly published before 2012 include -a (neuter gender, mostly 2nd declension); -ae (feminine gender, 1st declension); -i (masculine gender, 2nd declension); -es (masculine gender, 3rd declension). Other endings in use were found to be inaccurate in Judicial Opinion No. 128. For an overview see the underlying Request for an Opinion.
Below, the names of classes validly published under the ICNP are listed in groups according to the effective suffix, which is revealed by removing the expected stem from the name. (Note that this can be misleading if the stem ends in -i- and the authors actually used -ia but inadvertently dropped the final -i- from the stem; the suffix given in the list below is -a in such cases. However, most if not all of these names should have been orthographically corrected as of 2023.) Class names that do not contain the expected stem are marked as irregular. See also the LPSN introductory page about forming names.
Because of the large number of class names that would otherwise be illegitimate, it was considered that Rule 8 should not be retroactive. If so, names of classes validly published before 1 January 2012 would not need to conform to the "stem and -ia" scheme. In 2022, the ICSP decided to make Rule 8 non-retroactive. Hence, the listing below indicates whether or not a name was validly published prior to 2012. Names of classes validly published after 2011 and not conforming to the scheme enforced by Rule 8 are illegitimate in either case. Also note that there are other reasons why a name may be illegitimate and in particular why a name may be rejected.
Clostridia — Elusimicrobia — Halobacteria — Ignavibacteria — Methanobacteria — Thermodesulfobacteria — Thermomicrobia — Thermoplasmata
Abditibacteriia corrig. — Acidimicrobiia — Acidithiobacillia — Alicyclobacillia — Ardenticatenia — Atribacteria — Bacteriovoracia — Bacteroidia — Balneolia — Bdellovibrionia — Blastocatellia — Brachyspiria — Bradymonadia — Brevinematia — Calditrichia — Chitinispirillia — Chitinivibrionia — Chitinophagia — Chlamydiia — Chlorobiia — Chloroflexia corrig. — Conexivisphaeria — Coprothermobacteria — Coriobacteriia — Culicoidibacteria — Cytophagia — Deferrisomatia — Dehalococcoidia — Desulfarculia — Desulfitisporia — Desulfitobacteriia — Desulfobaccia — Desulfobacteria — Desulfobulbia — Desulfomonilia — Desulfotomaculia — Desulfovibrionia — Desulfurellia — Desulfuribacillia — Desulfurobacteriia — Desulfuromonadia — Dictyoglomeria corrig. — Dissulfuribacteria — Endomicrobiia corrig. — Fibrobacteria — Fimbriimonadia — Flavobacteriia — Fusobacteriia — Hydrogenophilia — Kiritimatiellia — Lentisphaeria — Leptospiria — Leptospirillia — Limnochordia — Longimicrobiia corrig. — Magnetococcia — Methanocellia — Methanonatronarchaeia — Methanosarcinia — Microcaldia — Nanobdellia — Natranaerobiia — Nitriliruptoria — Nitrososphaeria — Nitrospinia — Nitrospiria — Oligoflexia — Oligosphaeria — Peptococcia — Planctomycetia — Polyangiia corrig. — Rhodothermia — Rubrobacteria — Saprospiria — Sphingobacteriia — Spirochaetia — Sulfobacillia — Symbiobacteriia — Syntrophia — Syntrophobacteria — Syntrophomonadia — Syntrophorhabdia — Tepidiformia — Terriglobia — Terrimicrobiia corrig. — Thermaerobacteria — Thermincolia — Thermoanaerobaculia — Thermodesulfovibrionia — Thermoflexia — Thermoleophilia — Thermosediminibacteria — Thermosulfidibacteria — Tichowtungiia — Vicinamibacteria — Vulcanimicrobiia
Aquificia corrig. — Armatimonadia — Caldisericia — Chrysiogenia corrig. — Chthonomonadia corrig. — Erysipelotrichia — Gemmatimonadia corrig. — Ktedonobacteria corrig. — Opitutia corrig. — Synergistia — Thermolithobacteria — Verrucomicrobiia corrig.
Alphaproteobacteria — Betaproteobacteria — Deltaproteobacteria — Epsilonproteobacteria — Gammaproteobacteria — Mollicutes — Negativicutes
Alphabacteria — Anoxyphotobacteria — Arabobacteria — Archaeobacteria — Arthrobacteria — Chlorobacteria — Chlorobea — Chromatibacteria — Chroobacteria — Crenarchaeota — Deltabacteria — Epsilobacteria — Ferrobacteria — Firmibacteria — Flavobacteria — Hadobacteria — Halomebacteria — Hormogoneae — Methanothermea — Oxyphotobacteria — Planctomycea — Protoarchaea — Teichobacteria — Togobacteria