A total of 219 strains belonging to the genera Buttiauxella and Kluyvera were studied; 171 of these strains were isolated from mollusks, mainly snails and slugs, obtained from around the world. On the basis of DNA-DNA hybridization data, the strains were grouped into 11 genomospecies. A total of 44 phenotypic characters were used to differentiate the genera Buttiauxella and Kluyvera at the genus level and to identify genomospecies. There were significantly higher phenotypic probability distances between the genomospecies in the genus Battiauxella and the genomospecies in the genus Kluyvera than between the genomospecies in the same genus. Therefore, the existence of Buttiauxella and Kluyvera as different genera was confirmed. The existence of new species necessitated broadening the definitions of both genera. In two cases, Buttiauxella species could not be quantitatively differentiated biochemically, and several other pairs of species could be separated only by the results of one biochemical test. Nonetheless, combinations of several characteristics were used in differentiate all of the species with levels of certainly ranging from log 10.79 to log 57.77 (calculated as probability distances). The following new species are proposed: Buttiauxella ferragutiae (type strain, ATCC 51602 [DSM 9390]), Buttiauxella gaviniae (type strain, ATCC 51604 [DSM 9393]), Buttiauxella brennerae (type strain, ATCC 51605 [DSM 9396]), Buttiauxella izardii (type strain, ATCC 51606 [DSM 9397]), Buttiauxella noackiae (type strain, ATCC 51607 [DSM 9401]), Buttiauxella warmboldiae (type strain, ATCC 51608 [DSM 9404]), Kluyvera cochleae (type strain, ATCC 51609 [DSM 9406]), and Kluyvera georgiana (type strain, ATCC 51603 [DSM 9409]).