Nannoxyropsis acicula can be diagnosed from its congener N. ephippia by the absence of preopercle latero-sensory canal (vs. presence of sensory canal); and by enlarged odontodes on posterior margin of the parieto-supraoccipital, forming crest (vs. odontodes not enlarged or forming crest). It further differs from N. ephippia by having a longer head (34.8-39.4 vs. 29.4-33.5% SL), a narrower snout (width of snout measured at widest point of mouth opening (37.0-40.7 vs. 43.1-45.3% HL), a larger predorsal length (44.7-48.9 vs. 40.1-44.5% SL), a smaller dorsal interorbital distance (37.1-42.4 vs. 43.0-54.2% HL), 20-22 plates in median series of lateral plates (vs. 23), and 11-17 teeth on premaxilla (vs. 18-26) (Ref. 116855).