A Gram-stain-positive, non-spore-forming bacterium (strain RV113(T)) was isolated from the marine sponge Aplysina aerophoba. 16S rRNA gene sequence analysis showed that strain RV113(T) belongs to the genus Rubrobacter, and is related most closely to Rubrobacter bracarensis VF70612_S1(T) (96.9% similarity) and more distantly related (<93%) to all other species of the genus Rubrobacter. The peptidoglycan diamino acid was lysine. Strain RV113(T) exhibited a quinone system with menaquinone MK-8 as the predominant compound. The polar lipid profile of strain RV113(T) consisted of the major compounds phosphatidylglycerol and two unidentified phosphoglycolipids. The major fatty acid was anteiso-C17 : 0ω9c. These chemotaxonomic traits are in agreement with those of other species of the genus Rubrobacter. The results of physiological and biochemical tests allowed the clear phenotypic differentiation of strain RV113(T) from all recognized Rubrobacter species. Strain RV113(T) is thus considered to represent a novel species, for which the name Rubrobacter aplysinae sp. nov. is proposed. The type strain is RV113(T) ( = DSM 27440(T) = CECT 8425(T)).