Gracilicutes (Latin: gracilis, slender, and cutis, skin, referring to the cell wall) is a clade in bacterial phylogeny. 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, This classification system was abandoned in favour of the three-domain system based on molecular phylogeny started by C. Woese.