A yellow-coloured, marine actinobacterium, designated SST-45(T), was isolated from sandy sediment under the surface of a beach and taxonomically characterized by physiological, chemotaxonomic and phylogenetic methods. The cells of the isolate were Gram-positive, aerobic, non-sporulating, non-motile, spherical cells that occurred singly, in pairs, in clusters or as short chains. The isolate grew at 10-37 degrees C, an initial pH 5.1-12.1 and in the presence of 5 % (w/v) NaCl. The organism possessed LL-2,6-diaminopimelic acid as the diagnostic diamino acid in the cell wall, MK-8(H(4)) as the major menaquinone, a polar lipid profile including diphosphatidylglycerol, phosphatidylglycerol, phosphatidylinositol and an unknown phospholipid, C(18 : 1) and C(16 : 0) as the major fatty acids, and a DNA G+C content of 72.4 mol%. A phylogenetic analysis based on 16S rRNA gene sequences showed that the organism was related to members of the genera Marmoricola and Nocardioides. The closest neighbours were Marmoricola aurantiacus DSM 12652(T) (97.0 % sequence similarity) and Nocardioides jensenii KCTC 9134(T) (96.7 %). The combination of morphological and chemotaxonomic characters supported the assignment of the isolate to the genus Marmoricola. However, the organism is clearly distinguished phenotypically from the single described species of this genus, Marmoricola aurantiacus. Based on the data obtained, the organism has been assigned as a novel species, for which the name Marmoricola aequoreus sp. nov. is proposed. The type strain is strain SST-45(T) (=JCM 13812(T)=NRRL B-24464(T)).