Bythocypris polarsterni Brandão, 2008

Valves large; lateral outline of both valves rectilinear, subtrapezoidal; inequilateral, both anterior and posterior margins narrowly rounded, but anterior broader than posterior; dorsal margin broadly rounded, posterodorsal and anterodorsal margins straight, but without conspicuous angles; ventral margin straight in LV and fairly straight in RV. Adductor muscle scars subdivided but bythocypridid in aspect, occupying a very small area (less than 1/7 of valve height). Calcified inner lamella broad. Zone of concrescence very narrow, marginal pore canals straight and short. Radial pore canals simple, with wide rim. Appendages strongly pigmented, dark brown, conspicuous even through closed valves. antennula with slender thin podomeres I–II; very short podomeres IV–VII. Exopodite of antenna with 2 long and 1 short setae; podomere VI with 1 long, articulated claw, 1 short fused (!) claw, and 1 or 2 short thin setae. Base of mandibula with 1 dorsal seta, 1 or 2 bifurcate teeth, and 3 to 4 trifurcate teeth; palp podomere III elongated. Vibratory plate of maxillula with 4 or 5 strahlen and around 21 feathered setae. Vibratory plate of fifth limb with 4 strahlen and around 10 feathered setae. sixth and seventh limbs with 1 tiny seta on expodite. Furca with 3 short proximal setae, 1 long seta, and 3 medium-sized distal setae. One long seta between furcal rods. Genital lobe subhemispherical, with double coiled internal tube.