Rhamdella zelimai is distinguished from all its congeners by the hypertrophy of the rictal fold, mainly its lower portion consisting of a large and fleshy lobe whose posterior limit reaches the level of the transverse line through the preoperculomandibular sensory pore 5 and almost reaches the transverse plane through the base of the mental barbels (vs. lower portion of the rictal fold not hypertrophied). It can be further diagnosed from R. aymarae and R. rusbyi by having a shorter maxillary barbel in adults (barbel tip reaching from just anterior to just posterior the base of the pectoral-fin ray vs. tip falling short or reaching to vertical through dorsal-fin origin in R. aymarae or reaching to or passing the vertical through the posterior end of the dorsal-fin base in R. rusbyi); seven branchiostegal rays (vs. six); and inteorbital width 14.7?19.5% HL (vs. 31.0?44.9% in R. aymarae and 26.5?27.1% in R. rusbyi). It is further distinguished from R. aymarae by its larger horizontal eye diameter (18.8?24.4% of HL vs. 11.5?17.3%), shorter interdorsal length (10.0?12.6% SL vs. 16.9?23.4%), and longer adipose-fin base (32.2?36.0% SL vs. 18.5?27.9%); and from R. rusbyi, by its shorter pelvic fin (15.3?16.9% SL vs. 17.0?19.1%), longer anal-fin base (14.9?18.5% SL vs. 11.8?14.0%), the dorsal and ventral caudal-fin lobes subequal in both sexes (vs. dorsal caudal-fin lobe longer than the ventral lobe); and a distinct narrow dark mid lateral stripe (vs. stripe absent).

Rhamdella zelimai can be further differentiated from R. eriarcha by its premaxilla broader laterally, making the anterior margin of both premaxillae an almost straight line (vs. premaxilla homogeneously broad from mesial to lateral ends, so that the anterior margin of both premaxillae draw a gentle curve). It further differs from R. cainguae by the following characters: absence of the 'frontalsphenotic space' a distinct and large ovoid area in the supraorbital laterosensory canal between the frontal and sphenotic delimited by the apparently slender dorsal walls of these bones (vs. presence); by its larger interdorsal length (10.0?12.6% SL, mean = 11.1% vs. 7.6?10.3%, mean = 8.9%); shorter adipose-fin base (32.2?36.0% SL vs. 37.5?41.6%); shorter dorsal-fin base (11.2%?13.5% SL, mean = 12.4% vs. 13.3?16.5%, mean = 14.5%); shorter anal-fin base (14.9?18.5% SL vs. 18.6?22.0%); large internarial length (14.2%?16.6% HL vs. 21.6?24.7%); smaller internarial width (14.0?17.3% HL vs. 19.4?21.4%). It is also distinguished from R. longiuscula, by the dorsal and ventral caudal-fin lobes subequal in both sexes (vs. dorsal caudal-fin lobe longer than ventral lobe, mainly in males); and longer predorsal length (36.2?40.8% SL, mean = 38.0% vs. 31.6?37.0%, mean = 34.5%); from R. cainguae and R. aymarae by the absence of a dense concentration of long and slender papillae on the lateral body surface in the pectoral and abdominal regions (vs. presence of such papillae, resulting in a hairy aspect) (Ref. 98446).

Description: anal fin rays vi or vii, 8, 9, 10 or 11 (Ref. 98446).