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 nominative singular to nominative plural. A similar scheme was often applied to irregular names that are not derived from the name of a genus, as apparent in names ending in -bacteria (plural of bacterium) or in -cutes (plural of cutis). The grammatical gender of such class names varies; it is the one of their last component. In yet other cases the feminine plural ending -ae (first declension) was unexpectedly used.
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 did use -ia but inadvertently dropped the final -i- from the stem; the ending given in the list below is -a in such cases.) Names of classes that do not contain the expected stem are marked as irregular. See also the LPSN introductory page on forming names.
Because of the many names of classes that were illegitimate otherwise, it was considered to not regard Rule 8 as retroactive. If so, names of classes validly published before 1 January 2012 would not need to conform to the schema "stem and -ia". Hence the listing below indicates whether or not a name was validly published prior to 2012. Names of clases validly published after 2011 and not conforming to the scheme enforced by Rule 8 are illegitimate in either case.
Abditibacteriia corrig. — Acidimicrobiia — Acidithiobacillia — Ardenticatenia — Atribacteria — Bacteriovoracia — Bacteroidia — Balneolia — Bdellovibrionia — Blastocatellia — Chitinispirillia — Chitinivibrionia — Chitinophagia — Chlamydiia — Chloroflexia corrig. — Conexivisphaeria — Coprothermobacteria — Coriobacteriia — Culicoidibacteria — Cytophagia — Deferrisomatia — Dehalococcoidia — Desulfarculia — Desulfobaccia — Desulfobacteria — Desulfobulbia — Desulfomonilia — Desulfovibrionia — Desulfurellia — Desulfuribacillia — Desulfuromonadia — Dictyoglomeria corrig. — Dissulfuribacteria — Endomicrobiia corrig. — Fibrobacteria — Fimbriimonadia — Flavobacteriia — Fusobacteriia — Lentisphaeria — Limnochordia — Longimicrobiia corrig. — Methanonatronarchaeia — Nanobdellia — Nitriliruptoria — Nitrososphaeria — Oligoflexia — Oligosphaeria — Planctomycetia — Polyangiia corrig. — Rhodothermia — Rubrobacteria — Saprospiria — Sphingobacteriia — Spirochaetia — Syntrophia — Syntrophobacteria — Syntrophorhabdia — Tepidiformia — Terrimicrobiia corrig. — Thermoanaerobaculia — Thermoflexia — Thermoleophilia — Tichowtungiia — Vicinamibacteria
Alphabacteria — Arabobacteria — Arthrobacteria — Chlorobacteria — Chlorobea — Chromatibacteria — Chroobacteria — Crenarchaeota — Deltabacteria — Epsilobacteria — Ferrobacteria — Flavobacteria — Hadobacteria — Halomebacteria — Hormogoneae — Methanothermea — Planctomycea — Protoarchaea — Teichobacteria — Togobacteria