Tympanopleura cryptica is distinct from its congeners by having a unique combination of characters. It is distinguished from T. atronasus in having gill rakers on the first arch 21-26, mode 22 (vs. 14-23, mode 16 ), preanal vertebrae 14-15 (vs. 16-19); total vertebrae 38-41, mode 38 (vs. 39-43, mode 41); pleural rib pairs 4-5 (vs. 7-8), distance between pectoral- and dorsal-fin origin 21.6-24.3% SL (vs. 15.7-20.9% SL), and a uniform body coloration that does not include a dark blotch of melanophores on the flank above the anal-fin base or streaks in the caudal fin, as is typically present in T. atronasus. It can be diagnosed from T. brevis in having anal-fin rays 23-30 (vs. 31-36), pectoral-fin rays 8-10, mode 9 (vs. 10-12, mode 11), and total vertebrae 38 (vs. 38-41, mode 40). It differs from T. longipinna in having anal-fin rays 23-30 (vs. 32-42), pectoral-fin rays 8-10, mode 9 (vs. 10-13, mode 11), preanal vertebrae 14-15, mode 15 (vs. 13-15, mode 14), total vertebrae 38-41, mode 38 (vs. 40-43, mode 43), preanal length 59.6-66.0% SL (vs. 49.7-57.6% SL), distance between dorsal and adipose-fin origin 33.9-46.7% SL (vs. 46.5-54.0% SL), anal-fin base length 24.4-30.3% SL (vs. 33.9-39.9% SL), and eye diameter 16.7-25.6% HL (vs. 11.6-18.5% HL). It is distinguished from T. piperata in having anal-fin rays 23-30 (vs. 31-38), gill rakers on the first arch 21-26, mode 22 (vs. 16- 23, mode 19), total vertebrae 38-41, mode 38 (vs 39-41, mode 40), prepelvic length 48.4-53.6% SL (vs. 41.3-47.0% SL), prepectoral length 29.7-33.8% SL (vs. 23.6-28.3% SL), distance between pectoral and dorsal-fin origin 21.6-24.3% SL (vs. 15.2-20.9% SL), distance between dorsal-and adipose-fin origin 33.9-46.7% SL (vs. 45.9-55.4% SL), anal-fin base length 24.4-30.3% SL (vs. 30.9-39.3% SL), eye diameter 16.7-25.6% HL (vs. 24.3-35.7% HL), presence of two small posterior diverticula on gas bladder (vs. diverticula absent), and base of the caudal fin without a characteristic dark, hourglass-shaped transverse bar usually present in T. piperata. It differs from T. rondoni in having anal-fin rays 23-30, mode 29 (vs. 28-37, mode 31), pectoral-fin rays 8-10, mode 9 (vs. 10-13, mode 11), gill rakers on the first arch 21-26, mode 22 (vs. 24-33, mode 29-30), total vertebrae 38-41, mode 38 (vs. 38-42, mode 40), pleural rib pairs 4-5, mode 5 (vs. 4-6, mode 6), eye diameter 16.7-25.6% HL (vs. 8.4-17.0% HL), gas bladder cordiform and with two short posterior diverticula (vs. gas bladder elongated antero-posteriorly and with two longer, recurved diverticula), and pigmentation on the head and body diffuse and relatively uniform in appearance (vs. prominent spotted pattern) (Ref. 103256).