Diagnosis: Congoglanis inga differs from C. sagitta in having a longer maxillary barbel, reaching well past vertical through anterior margin of orbit vs. not reaching to orbit; a deeper caudal peduncle, 7-8% of standard length vs. 6%; and less slender caudal peduncle, its depth 2.1-2.9 times in its length vs. 3.1-4.0; a longer pelvic fin, 22-25% of standard length vs. 19-21%; a more posteriorly placed anal fin, anal-fin origin approximately at tip of adpressed pelvic fin vs. origin well in advance of tip of adpressed pelvic fin; longer anal-fin rays, posterior rays of adpressed anal fin extend well past vertical through posterior limit of adipose fin vs. posterior rays extend to, rarely slightly beyond, vertical through posterior limit of adipose fin; and fewer vertebrae, 35-37 vs. 39-41 (Ref. 88958). It differs from C. alula in having a longer maxillary barbel, reaching well past vertical through anterior margin of orbit vs. not reaching to orbit; a shorter pelvic fin, 19-21% of standard length vs. 24-28%; a longer postorbital length, 32-35% of head length vs. 27-31%; a relatively wide interorbital width, 2 times eye-diameter vs. 1.5 times; and longer anal-fin rays, posterior rays of adpressed anal fin extend well past vertical through posterior limit of adipose fin vs. posterior rays extend to, rarely slightly beyond, vertical through posterior limit of adipose fin (Ref. 88958).

Description: A relatively robust species, with body somewhat elongate, nearly cylindrical from head to anal-fin origin, with abdominal region slightly flattened, progressively tapering further posteriorly; greatest body depth and width located at dorsal-fin origin, except in specimens with distended abdomens; body smooth skinned and firm (Ref. 88958). Dorsal and ventral profiles of body from head to vertical through anal fin nearly horizontal but converge from vertical through anal-fin origin to posterior end of caudal peduncle; lateral line complete, running along midlateral surface of body; short, more-or-less uniformly spaced, dorsal and ventral branches extend off main portion of lateral line; body without dorsolateral or ventrolateral vertebral processes extending to skin surface from region of adipose-fin base posteriorly to caudal-fin base; caudal peduncle relatively short, thick, and compressed, but nearly as wide as high at terminus of anal-fin base; least depth of caudal peduncle approximately located at middle of its length (Ref. 88958). Head profile acutely triangular from dorsal view with lateral margin straight or slightly convex; snout tip rounded; head pointed and depressed from lateral view; snout moderately long, relatively slender and tapering anteriorly; eye horizontally elongated and situated entirely within posterior half of head; without free orbital margin; diameter of eye approximately one-half of interorbital distance; distance from posterior naris to anterior margin of eye only slightly less than distance between anterior naris and tip of snout; posterior naris closer to anterior naris than to eye; distance between nares of each side slightly more than one-half distance of each to contralateral naris; dorsal and lateral surface of head and body with scattered, tiny, white flattened tubercles, possibly free neuromast organs (Ref. 88958). Mouth subterminal, small, ovoid when open, with fleshy tuberculate upper lip and smooth firm lower lip, flanked to each side by tuberculate section; upper jaw with teeth in broad crescentic patch continuous across midline; lower jaw with teeth in oval patch on each side of symphysis, with narrow median gap; teeth in both jaws long, slender and slightly curved; numbers of teeth in upper and lower jaws about equal; barbels tuberculate and distally tapered; maxillary barbel longest, reaching well past vertical through anterior margin of eye and extending to, or nearly to, margin of branchiostegal membrane; inner mandibular shortest, with base situated slightly lateral of midline and approximately in line with lateral margin of smooth portion of lower lip; outer mandibular barbel arises from angle of mouth and extends posteriorly approximately one-half distance to branchiostegal membrane; branchiostegal membrane continuous across ventral midline, with central portion of posterior margin straight or slightly concave; gill slit extends posterodorsally to horizontal through eye; supraoccipital process elongate and slightly wider near posterior tip; process separated by small gap from small triangular nuchal shield (Ref. 88958). Dorsal fin falcate, first branched ray longest; tip of adpressed dorsal fin extends past vertical through base of pelvic fin; first dorsal-fin ray segmented, not forming spine; adipose-fin origin located at vertical through anal-fin origin; fin small, length of fin base approximately one-half distance between posterior terminus of dorsal-fin base and adipose-fin origin; adipose fin adnate, posterior limit of fin situated posterior of vertical through anal-fin base, but not past posterior of vertical through tip of adpressed anal fin; pectoral fin large and falcate, with first ray curved, pectinate, broad and with fleshy pad covering ventral surface; distal margin of fin slightly concave, with first ray longest; innermost pectoral-fin rays short, posterodorsally oriented and adpressed to body wall; tip of adpressed pectoral fin falling short of pelvic-fin origin and reaching to vertical through posterior terminus of dorsal-fin base; pelvic fin large, but markedly smaller than pectoral fin; distal margin slightly concave, with first ray longest; first pelvic-fin ray curved and pectinate, with ventral surface covered by fleshy pad; pelvic-fin origin located distinctly posterior of vertical through posterior end of dorsal-fin base; tip of adpressed pelvic fin extends to, or slightly beyond, anal-fin origin; anal fin small, with distal margin straight; tip of adpressed anal fin extends past vertical through posterior base of adipose fin; anal-fin base approximately one-half length of adipose-fin base; caudal fin deeply forked, asymmetrical, with ventral lobe longer and broader than dorsal lobe; fin lobes acutely pointed; middle rays of caudal fin slightly less than one-half length of longest rays of dorsal lobe; dorsal-fin rays i,6-7 or i,6,i; pectoral-fin rays i,11-12; pelvic-fin rays i,5; anal-fin rays iv,6-7; principal caudal-fin rays i,7,8,i; vertebrae 35-37; ribs 11-12 (Ref. 88958).

Colouration: Body colouration generally dark, with variably distinct lighter regions on overall dark brown body; in lightly pigmented specimens, body darker dorsally with brown colouration extending ventral of lateral line on abdomen and caudal peduncle; boundary between dark brown pigmentation of dorsal and dorsolateral regions and lighter colouration of ventrolateral and ventral regions relatively straight and horizontal from pectoral-fin base to caudal peduncle; darker individuals with boundary obscured and appearing to extend further ventrally before gradually becoming somewhat lighter (Ref. 88958). Lightly pigmented specimens with six pale patches distributed in irregular horizontal line along dorsolateral part of body; anteriormost patch ovoid, horizontally elongated, extending just dorsal of lateral line anterior of dorsal-fin origin; second patch vertically elongated, located just past posterior extent of dorsal-fin base; patch extends dorsally to midline, appearing as saddle in dorsal view; third patch horizontally elongate, slender; patch extending above lateral line from immediately posterior of second patch to past middle of interspace between dorsal-fin base and adipose-fin origin; fourth patch somewhat more dorsally placed than third; contralateral fourth patches in contact along dorsal midline and form saddle immediately anterior of adipose-fin base; fifth patch extends from level of middle of adipose fin past posterior extent of that fin; patch horizontally elongate, entirely above lateral line; sixth patch small and round, positioned immediately anterior of caudal-fin base near dorsal midline; in darkly pigmented specimens, pale patches quite obscured, with some or all barely visible; ventrolateral portion of abdomen and ventral part of caudal peduncle with scattered dark chromatophores, but chromatophores absent on ventral portion of abdomen as far posterior as pelvic fin, even in darker examined specimens; lateral-line canal with pale superficial canal branches (Ref. 88958). Dorsal and lateral portions of head dark brown other than for variably shaped pale spot immediately posterior of eye; spot smaller than, to approximately same size as, eye; ventral part of head pale with distinct horizontal line between brown and pale portions ventrolaterally; maxillary barbel dusky, especially dorsally; mandibular barbels unpigmented (Ref. 88958). Dorsal surfaces of pectoral- and pelvic-fin rays brown, without pattern except for pale distal margins; ventral surface of pectoral fin without chromatophores except for small patch along basal portion of innermost rays; ventral surface of pelvic fin without chromatophores (Ref. 88958). Dorsal fin with dense concentrations of dark chromatophores along anterior rays; interradial membranes and posterior rays without chromatophores; adipose fin darkly pigmented, except for fine pale distal margin; anal fin with dense concentration of dark chromatophores along anterior rays; posterior rays without chromatophores; caudal fin with broad dark stripes running along length of unbranched principal rays and adjacent branched rays; middle rays dusky (Ref. 88958).