Neoplecostomus doceensis can be distinguished from all its congeners by the presence of enlarged, fleshy folds between dentaries in all specimens, more evident in mature males (vs. absence of the enlarged fleshy folds). It also differs from all congeners by the presence of two or three series of well-developed papillae anterior to premaxillary teeth (vs. papillae poorly developed or absent). Other characters useful for its identification from other congeners include: presence of a fully-developed adipose fin (vs. lacking or reduced adipose fin in N. botucatu and N. paranensis); moderately-sized odontodes along lateral margins of snout and snout without swollen skin in mature males (vs. presence of large-sized odontodes surrounded by swollen skin along lateral margins of snout in mature males of N. selenae); a well-developed dorsal-fin spinelet, wider than dorsal-fin spine base (vs. absent or narrower than dorsal-fin spine base in N. franciscoensis and N. ribeirensis); 12-35 dentary teeth (vs. 5-12 in N. microps and 7 in N. variipictus); 25-29 lateral-line plates (vs. 34-43 in N. granosus); presence of a developed membrane on the dorsal portion of the first, second and third pelvic-fin branched rays (vs. absence in N. langeanii) (Ref. 106072).