Beschreibung: A Gram-stain-positive bacterium, strain RV15T, forming an extensively branched substrate mycelium and aerial hyphae that differentiate into spiral chains of spores, was isolated from a marine sponge Dysidea tupha collected from Rovinj (Croatia). Comparison of 16S rRNA gene sequences showed that strain RV15T is a member of the genus Streptomyces with highest sequence similarity to the type strains of Streptomyces caeruleatus (98.8 %), Streptomyces cyaneochromogenes (98.6 %) and Streptomyces shaanxiensis (98.5 %). Sequence similarities to all other Streptomyces types strains were below 98.5 %. The multilocus sequence analysis-based evolutionary distance, the average nucleotide identity value and the genome-to-genome distance of strain RV15T and the type strain of S. caeruleatus were clearly below the species cut-off values. Strain RV15T exhibited a quinone system composed of the major menaquinones MK-9(H4), MK-9(H6) and MK-9(H2), typical for the genus Streptomyces. The polar lipid profile of strain RV15T consisted of the predominant compounds diphosphatidylglycerol and phosphatidylethanolamine, mod-erate amounts of phosphatidylinositol, phosphatidylinositol mannoside, an unidentified lipid and an unidentified phospholipid. Major polyamines were spermine and spermidine. The diagnostic diaminoacid of the peptidoglycan was meso-diaminopimelic acid. The major fatty acids were iso C16: 0, anteiso C17: 1 ω9c and anteiso C17: 0. The results of physiological and biochemical tests allowed further phenotypic differentiation of strain RV15T from its most-related species and hence clearly merits species status. We propose the name Streptomyces dysideae sp. nov. with the type strain RV15T (=DSM 42110T=LMG 27702T).