Shell thick-walled, opaque, lenticular or discoidal, with short spicules. Surface covered with subcircular to oval deep, funnel-shaped pits. Six main spicules equal in shape and size, massive, usually smooth, less often faintly edged or keeled, tips bluntly rounded, sometimes two equatorial spicules longer and thicker than other four main (polar) spicules. Secondary spicules much shorter and thinner than main (they brake off and dissolve easily, therefore often lacking). Diameter of shell (excluding spicules): 0.11 mm; length of main equatorial spicules: 0.1 mm, polar: 0.08 mm, secondary: 0.06 mm.