Microlepidogaster discontentais distinguished from all congeners by having odontodes on the caudal peduncle conspicuously arranged in longitudinal lines (vs. not arranged in longitudinal lines) and a shorter pectoral-pelvic fins distance (10.6-12.8 vs. 13.0-18.7 % SL). It can be further diagnosed from all congeners, except M. longicolla by its wide naked area on the tip of the snout (vs. an inconspicuous naked area or a rostralplate) and anterior portion of the compound first dorsal-fin pterygiophore articulating to the neural spine of the tenth vertebral centrum (vs.articulating to the neural spine of the eighth or ninth centrum in M. perforate, ninth centrum in M. arachas, and seventh centrum in M. dimorpha). It differs from all congeners,except M. arachas, by having smaller interorbital distance (31-37 % HL vs. 48-53 in M. perforata, 39-43 in M. longicolla, and 39-45 in M. dimorpha). It further differs from M. perforataand M. longicollaby having smaller prenasal length (29-32 % HL vs. 42-49 and 45-49, respectively), and from M. dimorphaand M. arachasby having more slender caudal peduncle depth(depth 6.3-7.3 % SL vs. 10.0-11.4 and 8.1-10.3, respectively). Other diagnostic characters useful to differentiate it from M. arachasand M. longicolla include fewer dentary teeth (9-14 vs. 18-29 and 16-29, respectively), and from M. perforataand M. dimorpha include an axillary slit of the pectoral fin in juveniles (up to 2.56 cm SL) but absent in adults (vs. pectoral axillary slit persistent, presentin both juveniles and adults). It is also distinct from M. perforata by having the middle series of lateral plates complete, reaching the end of the caudal peduncle (vs. middle series of lateral plates ending two plates before the base of the caudal fin); and from M. arachasby having narrower head (width 61-66 % HL vs. 71-80) (Ref. 98822).