A novel marine actinomycete, designated B374(T), was isolated from a marine sponge, Glodia corticostylifera, which was collected from São Paulo, Brasil. The taxonomic position of B374(T) was established by using data derived from a polyphasic approach. The organism showed a combination of chemotaxonomic and morphological characteristics consistent with its classification in the genus Marmoricola and it formed a distinct phyletic line in the clade of the genus Marmoricola, based on 16S rRNA gene sequences. Strain B374(T) was most closely related to Marmoricola aequoreus SST-45(T) (98.5% 16S rRNA gene sequence similarity), but was distinguished from this strain and from the other type strains of species of the genus Marmoricola on the basis of a combination of phenotypic properties. The data obtained, therefore, indicates that isolate B374(T) ( = CBMAI 1089(T) = DSM 28169(T)) should be classified as a novel species of the genus Marmoricola, for which the name Marmoricola aquaticus sp. nov. is proposed.