Marophrys is a genus of spicules-bearing centrohelids belonging to Heterophrys-like organisms (HLO's). Here Marophrys nikolaevi spec. nov. is described. Four strains were isolated from brackish waters (16–22 ppt) of the Tuzlukkol’ River, the Tuzluchnoe Lake (South Urals, Russia) and the Black Sea. All the strains were characterised with light microscopy and electron microscopic study of the whole mount preparations. Molecular phylogenetic analysis has put SSU rDNA sequences, obtained for all strains, inside Marophryidae clade sister to M. marina. The organisms have a cell diameter of 4–11 μm and are surrounded with organic spicules of two types. Short (0.6–0.7 μm) and thin (0.01–0.02 μm) mostly tangentially oriented spicules form a lax sheath, surrounding the cell. Longer (3–6 μm) and thicker (0.04–0.05 μm) spicules are embedded in this sheath and are radially or obliquely oriented. Energy-dispersive X-ray analysis has shown that the spicules are purely organic. The taxonomy of marine Heterophrys-like organisms is discussed.