Cryptancistrus similis is diagnosed by having a unique barcode sequence (GBOL736-14). It differs from all other species under Hypostominae by the following combination of characters : dorsoventrally depressed head and body; no prominent ridge or crest formed on head and body plates; rounded snout, covered with contiguous plates except tip region, and posterior part of lateral margin of snout; latter area forming a soft fleshy border, and bearing slightly enlarged odontodes associated with small fleshy tentacules sensu; odontodes over a broad area on the opercle present; numerous enlarged cheek odontodes supported by evertible plates present; odontodes straight with tips slightly curved, as opposed to strongly hook-shaped; whisker-like cheek odontodes lacking; enlarged odontodes along snout margin absent; dorsal iris operculum present; lips forming an oval disk; numerous viliform and bicuspid teeth on dentary and premaxillary; a small buccal papilla present, enlarged dentary papilla absent; dorsal fin with seven branched rays; adipose fin present; membranous extension between end of dorsal fin and adipose fin absent; five series of lateral plates extending to caudal fin; lateral plates not keeled and not bearing enlarged odontodes; angular but not keeled lateral plates of ventral series on caudal peduncle; abdominal region entirely naked. It morphologically closely resembles species of Guyanancistrus but it differs from them primarily by the fleshy posterior part of lateral margin of snout bearing slightly enlarged odontodes associated with small fleshy tentacules (vs. plates along margin of snout forming a rigid armour covered with minute odontodes, absence of tentacules). It can be further diagnosed from all species of Guyanancistrus by a skin region bordering the exposed portion of opercle roughly as large as the latter (vs. distinctly narrower than the latter) (Ref. 116863).

Description: pelvic i,5; anal i,5 (Ref. 116863).