Diagnosis: Hypostomus melanephelis is distinguished from the congeners, except H. interruptus, H. paucimaculatus, H. micropunctatus, H. nigropunctatus, and H. rhantos, by having conspicuous dark, roundish and tiny (smaller than eye pupil) set of dark spots on trunk (vs. medium to large pale or dark spots [larger than eye pupil], or transversally elongated dark spots); Hypostomus melanephelis is distinguished from H. interruptus, H. paucimaculatus, H. micropunctatus, H. nigropunctatus, and H. rhantos by the naked to partially plated abdomen (vs. abdomen completely covered by platelets); it is further diagnosed from H. interruptus by a larger mandibular ramus, 18-22 % HL (vs. 11.6-17.5 % HL; from H. paucimaculatus by having villiform bicuspid non spoon-shaped teeth with the lateral cusps not fused to the mesial tooth (vs. massive spoon-shaped teeth with lateral cusps usually fused to the mesial tooth); from H. micromaculatus by having usually 1 row of spots on each interradial membrane of dorsal fin (vs. 4-5) moderately distant from each other on flanks (vs. densely settled spots); from H. nigropunctatus by having just 1 plate posteriorly bordering supraoccipital (vs. 3); and from H. rhantos by having a more depressed head 49-56 % SL (vs. a more deeper head 64.3-83.2 % HL (Ref. 103391).

Description: head broad and considerably depressed; body width in cleithral region significantly greater than head depth and approximately equal to head length; snout and anterior profile of head in dorsal view rounded in smaller specimens to somewhat square-shaped in larger individuals; snout rising at approximately 45° from horizontal in lateral profile; dorsal profile slightly convex and sloped upward from snout tip to interorbital region, straight to slightly convex from that point to dorsal-fin origin; sloped downward from dorsal-fin origin to region just anterior of dorsal procurrent caudal-fin rays, then elevating again to caudal-fin insertion; caudal peduncle somewhat octagonal in crossection, dorsally and ventrally flattened; eye of moderate size, dorsolaterally positioned; interorbital space slightly concave, orbit barely raised; mesethmoid forming inconspicuous median bulge on snout; pair of ridges on dorsal surface of head, from lateral margin of nares to anterodorsal margin of eyes, and from that through superior portion of pterotic-supracleithrum; cheek plates usually with slightly developed odontodes; supraoccipital generally flat, with moderate posterior process, bordered by large single plate; dorsal and lateral surfaces of head and body covered with dermal plates, except for small naked patch on tip of snout and at dorsal-fin base; predorsal region with paired, poorly developed ridges; body lateral surface with 5 longitudinal series of plates; dorsal series of plates dorsally flattened from posterior end of dorsal-fin base to procurrent caudal-fin rays; mid-dorsal series with slightly developed longitudinal rows of odontodes on median portion of each plate; median row of odontodes slightly upwardly oriented from 3rd to 5th plate; median series without rows of odontodes and sequentially bearing lateral-line pores; lateral line complete; mid-ventral series with 1st 5 plates bent, without rows of odontodes to caudal peduncle; ventral series gently bent, flattened, without rows of odontodes; mouth moderately wide; median buccal papilla moderately developed; lips moderate to large; outer edge of upper lip with odontodes; lower lip almost reaching gill openings line; lower lip inner surface covered with numerous small papillae, larger proximal to dentary; maxillary barbel moderate in size, just shorter than orbital diameter; teeth slender, with elongated main cusp and smaller than lateral cusp; intermandibular tooth row angle approximately 150°; lower surface of head naked in smaller specimens, with small to moderate patches of platelets immediately anterior to gill openings in larger specimens; abdomen largely naked; scapular bridge usually naked up to 90.0 mm SL; larger specimens with platelets progressively appearing on scapular bridge on different areas on abdomen; abdomen coverture progressing anteriorly from scapular bridge towards branchial opening and posteriorly along sides of abdomen towards pelvic fin insertion; dorsal fin II,7, moderate in size, its distal border slightly convex, when adpressed reaching azygous plate of adipose fin in smaller specimens or just about on larger specimens; spine flexible; adipose-fin spine inflexible and well developed, slightly curved and backwardly oriented, with distal tip usually ending 2 plates away from 1st dorsal procurrent caudal-fin ray; pectoral fin I,6 and arrow-shaped, with distal rays much longer than proximal ones, its distal border straight, pectoral-fin spine inflexible, slightly curved with rounded tip, and usually with distally moderately developed odontodes, specially in larger specimens, when adpressed reaching to approximately middle of pelvic-fin spine; pelvic fin i,5 with similar-sized rays, its distal border straight to slightly convex, pelvic-fin spine flexible, curved inward, when adpressed just reaching anal-fin insertion; anal fin i,4, when adpressed, distal tip of posterior rays reaching 4th or 5th plate posterior to its origin; caudal fin i,7+7+i, emarginate; total vertebrae 29 (in 4 c&s specimens) (Ref. 103391).

Coloration: Color in alcohol: Ground color of dorsal surface of head and body light brown; head, dorsum and flanks covered with numerous small, dark, sharp and round spots; spots of similar size (smaller than nare diameter) on head, trunk and fins; on head, more numerous and densely organized; well-spaced on trunk and fins; dorsal fin with few spots disposed in a single line along each inter-radial; spots absent on rays; in some specimens, spots on dorsal fin may be concentrated on proximal region; dorsal, pectoral and pelvic fins with spots similar to overall body pattern; pectoral spine with spots on its dorsal surface; adipose and anal fins usually without spots; caudal fin usually with few dark spots in specimens up to 100.0 mm SL; larger specimens usually devoid of spots; presence of a broad longitudinal dark brown band on inferior lobe of caudal fin running parallel to outermost 2 or 3 branched rays, not easily seen in specimens up to 150.0 mm SL; in some specimens up to 120.0 mm SL lower lobe of caudal fin slightly darker than upper lobe; ventral region of body and fins without spots; most specimens with 5 faded oblique dark bars on dorsum, 1st bar on posterior portion of head, originating at middle of orbit, 2nd bar at 1st dorsal-fin branched rays, 3rd bar at last dorsal-fin branched ray, 4th bar at anterior region of adipose-fin and 5th at procurrent caudal-fin rays (Ref. Ref. 103391). Color in life: similar coloration as in preserved specimens, just more yellowish brown colored (Ref. Ref. 103391).