Polychaetes associated with Sarcotragus muscarum Schmidt, 1864 were collected from seven sites along the Turkish Aegean coast. The sponge cavities and surfaces contained 89 polychaete species belonging to 23 families. Among the families, Syllidae comprised 21.8% of the species, while Nereididae accounted for 22.8% of the individuals. Ceratonereis costae was the dominant species in 50% of the samples and also had the highest frequency index value. The number of polychaete species and individuals, and the diversity index (H') were positively correlated with the sponge volume. The similarity among the stations, and the ecological indices between the samples were compared.