Various definitions, see text Gracilicutes (Latin: gracilis, slender, and cutis, skin, referring to the cell wall) is a clade in bacterial phylogeny.

[2] Traditionally gram staining results were most commonly used as a classification tool, consequently until the advent of molecular phylogeny, the Kingdom Monera (as the domains Bacteria and Archaea were known then) was divided into four phyla,[1][3] This classification system was abandoned in favour of the three-domain system based on molecular phylogeny started by C.

[5][6] Using hand-drawn schematics rather than standard molecular phylogenetic analysis, Gracilicutes was revived in 2006 by Cavalier-Smith as an infrakindgom containing the phyla Spirochaetota, Sphingobacteria (FCB), Planctobacteria (PVC), and Proteobacteria.

Also as noted above, the use of Gracilicutes by Cavalier-Smith can be rejected because it was a major alteration of an earlier taxonomic name, was not based on a statistical analysis, and did not follow the three-domain system.

Spirochaetota Poribacteria FCB/"Sphingobacteria" PVC/"Planctobacteria" Elusimicrobiota Aerophobetes Rokubacteria Acidobacteriota Aminicenantes Dadabacteria Thermodesulfobacteriota Myxococcota Modulibacteria Tectomicrobia Nitrospinota Nitrospirota Chrysiogenota Deferribacterota Dependentiae Campylobacterota Aquificota (sometimes included in Terrabacteria.)

Cavalier-Smith's Tree of Life, 2006[cstol 1] Chlorobacteria Hadobacteria Cyanobacteria Spirochaetae Sphingobacteria (FCB) Planctobacteria (PVC) Proteobacteria s.l.

Eurybacteria Endobacteria (Bacillota) Actinobacteria Archaea Eukarya Legend: [A] Gram-negative with a peptidoglycan cell wall like Chlorosome.