The census of shallow-water sponges from the northern Aegean and Marmara sea coasts resulted in the collection of 10 species of Demospongiae. A new Hymedesmia species, Hymedesmia (Hymedesmia) anatoliensis sp. nov., is described from the western coast of Turkey. Three further species of demosponges, Axinyssa aurantiaca (Schmidt, 1864), Halichondria (Halichondria) contorta (Sarà, 1961), and Dictyonella incisa (Schmidt, 1880), are new to the sponge fauna of Turkey.