Four strains of nonmotile, prosthecate bacteria were isolated in the 1970s and assigned to the genus Prosthecobacter. These strains were compared genotypically by DNA/DNA reassociation and 16S rDNA based phylogenetic analyses. Genotypic comparisons were complemented with phenotypic characterizations. Together, these studies clearly indicate each Prosthecobacter strain represents a novel species of bacteria. We propose three new species of Prosthecobacter, P. dejongeii strain FC1, P. vanneervenii strain FC2, and P. debontii strain FC3; P. fusiformis is reserved for the type strain of the genus, strain FC4. Additionally, we propose the genera Prosthecobacter and Verrucomicrobium, currently members of the order Verrucomicrobiales, to comprise a novel higher order taxonomic group, the division Verrucomicrobia div. nov. and the class Verrumicrobiae class nov. Many novel members of the Verrucomicrobia, as revealed by molecular ecology studies, await isolation and description.