A novel, Gram-positive bacterial strain, F12(T), was isolated from the abdominal epidermis of a sea cucumber, Holothuria edulis, collected from seawater off the coast of Japan. According to 16S rRNA gene sequence analysis, this strain represents a novel, deep-rooting lineage within the class Actinobacteria and clusters with uncultured bacteria and Acidimicrobium ferrooxidans. Compared to species with validly published names, the highest 16S rRNA gene sequence similarity (89.8 %) was to Acidimicrobium ferrooxidans DSM 10331(T). Phylogenetic analyses showed that strain F12(T) represents a distinct phylogenetic lineage related closely to the genus Acidimicrobium. Strain F12(T) contained MK-9(H(6)) as the major menaquinone, whilst 17 : 0, 17 : 1omega8c, 15 : 0 and 16 : 0 were the major cellular fatty acids. The cell-wall peptidoglycan of strain F12(T) was composed of meso-diaminopimelic acid as the diagnostic diamino acid, alanine and glutamic acid (1 : 2 : 1). The cell-wall sugars detected were rhamnose, mannose, arabinose, galactose and xylose. The G+C content of the DNA was 74.4 mol%. From the taxonomic data obtained in this study, the name Iamia majanohamensis gen. nov., sp. nov. is proposed for the isolate, with type strain F12(T) (=NBRC 102561(T)=DSM 19957(T)). The name Iamiaceae fam. nov. is also proposed for the distinct phyletic line represented by the genus Iamia.