Revised Taxonomy of the Class Mollicutes: Proposed Elevation of a Monophyletic Cluster of Arthropod-Associated Mollicutes to Ordinal Rank (Entomoplasmatales ord. nov.), with Provision for Familial Rank To Separate Species with Nonhelical Morphology (Entomoplasmataceae fam. nov.) from Helical Species (Spiroplasmataceae), and Emended Descriptions of the Order Mycoplasmatales, Family Mycoplasmataceae Tully, Joseph G. and Bové, Joseph M. and Laigret, FréDéRic and Whitcomb, Robert F.,, 43, 378-385 (1993), doi = https://doi.org/10.1099/00207713-43-2-378, publicationName = Microbiology Society, issn = 1466-5026, abstract= Abstract On the basis of recent phylogenetic studies of 47 species within the class Mollicutes and recent molecular and physiologic findings that distinguish a new group of non-sterol-requiring insect and plant mollicutes from Acholeplasma species, we propose a revised taxonomy of the class Mollicutes. Order I (Mycoplasmatales) is retained as described earlier (S. Razin and E. A. Freundt, p. 740–742, in N. R. Krieg and J. G. Holt, ed., Bergey’s Manual of Systematic Bacteriology, vol. 1, 1984), with provision for a single family (Mycoplasmataceae) and two genera (Mycoplasma and Ureaplasma) for classification of sterol-requiring mollicutes primarily associated with vertebrates. Emended descriptions of the order and family for the above taxa are hereby included. Proposed order II (Entomoplasmatales ord. nov.) contains subtaxa for either nonhelical (Entomoplasmataceae fam. nov.) or helical (Spiroplasmataceae) mollicutes; the latter family is hereby transferred from the order Mycoplasmatales. The new order and family permit designation and classification of a monophyletic cluster of mollicute strains associated primarily with arthropods. It is proposed that nonhelical, sterolrequiring insect and plant mollicutes previously designated Mycoplasma ellychniae (Tully et al., 1989), Mycoplasma melaleucae (Tully et al., 1990), Mycoplasma somnilux (Williamson et al., 1990), Mycoplasma luminosum (Williamson et al., 1990), and Mycoplasma lucivorax (Williamson et al., 1990) be transferred to Entomoplasma gen. nov., family Entomoplasmataceae fam. nov., as Entomoplasma ellychniae comb, nov., Entomoplasma melaleucae comb, nov., Entomoplasma somnilux comb, nov, Entomoplasma luminosum comb, nov., and Entomoplasma lucivorax comb. nov. Furthermore, the genus Mesoplasma gen. nov. within the family Entomoplasmataceae fam. nov. is proposed for four non-sterol-requiring insect and plant mollicutes. This designation requires the transfer of Acholeplasma florum (McCoy et al., 1984), Acholeplasma entomophilum (Tully et al., 1988), Acholeplasma Sciffertii (Bonnet et al., 1991), and Mycoplasma lactucae (Rose et al., 1990) to Mesoplasma florum comb, nov., Mesoplasma entomophilum comb, nov., Mesoplasma Sciffertii comb, nov., and Mesoplasma lactucae comb, nov., respectively. Previously established orders Acholeplasmatales and Anaeroplasmatales within the class Mollicutes are designated orders III and IV, respectively, in the proposed revision. Classification and characteristics of lower taxa within these two orders remain as previously given. The proposal outlined here does not consider the large cluster of nonculturable, arthropod-associated, plant-pathogenic mollicutes (“mycoplasma-like organisms”) recently shown to be more closely related to members of the order Acholeplasmatales., language=, type=