Distinguished from its congeners, Rhamdiopsis microcephala and Rhamdiopsis moreirai by the possession of the following characters: ethmoid cartilage discontinuous; eyes absent and optic foramen atrophied; longer barbels, length of maxillary barbel 32.2-43.3% SL; supraorbital and infraorbital sensory canals not connected to each other anteriorly; presence of s7 branch and pore of the supraorbital laterosensory canal; no subpreopercle; anterior and posterior branches of the transverse process 4 co-ossified to each other; posterior limb of transverse process 4 undivided, with spatulated shape; posterolateral corner of posterior portion of the posterior branch of the transverse process of vertebra 4 extending approximately to midlength of the transverse process of vertebra 5; presence of a widely exposed pseudotympanum; dorsal fin larger, dorsal-fin base 11.2-14.1% SL and length of third dorsal-fin ray 14.4-18.7% SL; posterior lobe of the adipose fin straight; anal fin deep and rounded; shorter anal-fin base, supported typically by 14-15, less commonly 13 or 16-17 rays; hypural 5 usually co-ossified to hypural 4 at its distal portion; dorsal hypural plate typically with 7, rarely 6 or 8 rays; dorsal caudal-fin lobe typically with 6, rarely 4, 5 or 7 branched rays; ventral caudal plate typically with 6, rarely 7 rays; ventral

caudal-fin lobe typically with 6, rarely 4 or 5 branched rays; body relatively shorter, with 38-40 vertebrae; lateral line very short, with 5-15 pores, usually reaching from the vertical through posterior region of pseudotympanum to the vertical through dorsal-fin origin; fatty tissue

broadly spread through the body; adults of small body size, reaching 3.85 cm SL; body unpigmented; non-cryptobiotic behavior, expressed by marked midwater activity; non-photophobic behavior; poorly-developed circadian rhythms; and life in lentic habitat. Differs also from Rhamdiopsis microcephala by its epiphyseal branches of supraorbital laterosensory canals not fused to each other, each one bearing its own pore, the s6 pore, and basal third of the posterior border of the adipose fin connected with the dorsal fold of caudal fin, leaving a large, almost complete free posterior lobe (Ref. 86271).