Diagnosis: Congoglanis alula differs from C. inga in having a shorter maxillary barbel not reaching to vertical through anterior margin of orbit, vs. extending well past anterior margin of orbit, respectively; a longer pelvic fin, 24–28% of standard length, vs. 19–21%; a shorter postorbital length, 27–31% of head length, vs. 32–35%; a relatively narrow interorbital width, 1.5 times eye diameter, vs. 2 times; and shorter anal-fin rays, posterior rays of adpressed anal fin extend to, rarely slightly beyond, vertical through posterior limit of adipose fin, vs. posterior rays extend well past vertical through posterior limit of adipose fin (Ref. 88958). Congoglanis alula differs from C. sagitta in having a longer pectoral fin, 28–29% of standard length, vs. 23–27%; a longer pelvic fin, 24–28% of standard length, vs. 19–21%; a shorter caudal peduncle, 18–22% of standard length, vs. 21–24%; and deeper caudal peduncle, caudal-peduncle depth 2.6–3.3 times in caudal-peduncle length, vs. 3.1–4.0 times; a relatively narrow interorbital width, 1.5 times eye diameter, vs. 2 times; 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; and fewer vertebrae, 36–39, vs. 39–41 (Ref. 88958).

Description: Body 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; 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 moderately elongate, thick, and compressed, but nearly as wide as high at terminus of anal-fin base; least depth of caudal peduncle located approximately at posterior of peduncle (Ref. 88958). Head profile acutely triangular from dorsal view with lateral margin slightly convex; snout tip rounded; head pointed and depressed from lateral view; snout moderately long, relatively slender and tapering anteriorly; eye slightly horizontally elongated and situated entirely within posterior one-half of head; without free orbital margin; diameter of eye approximately two-thirds of interorbital distance; distance from posterior naris to anterior margin of eye only slightly greater 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 less than one-half distance of each to contralateral naris; dorsal and lateral surface of head and body with scattered, tiny, white flattened tubercles (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 falling short of vertical through anterior margin of eye; inner mandibular barbel 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 to vertical through tip of maxillary barbel; 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 narrow 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 with length of base approximately one-half distance between posterior terminus of dorsal-fin base and adipose-fin origin; adipose fin adnate, ovoid, with posterior limit of fin base posterior of vertical through anal-fin base, but not 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 but reaching to vertical through posterior terminus of dorsal-fin base; pelvic fin large, only slightly 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 middle of anal-fin base; anal fin small, with distal margin straight; tip of adpressed anal fin extends past vertical through posterior limit of adipose fin; anal-fin base approximately two-thirds length of adipose-fin base; caudal fin deeply forked, asymmetrical, with ventral lobe variably longer and broader than dorsal lobe; fin lobes long and acutely pointed; middle rays of caudal fin slightly less than one-half length of longest rays of dorsal lobe; dorsal-fin rays i,6,i or i,7; pectoral-fin rays i,11-12 or i,11,i; pelvic-fin rays i,5; anal-fin rays iii-iv,5-6,i of iii-iv,6-7; principal caudal-fin rays i,7,8,i; vertebrae 36-39; ribs 11-13 (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 rounded or slightly horizontally elongated, located just past posterior extent of dorsal-fin base; third patch horizontally elongated and slender; patch extending above lateral line from vertical through pelvic-fin origin to vertical through midlength of adpressed pelvic fin; ventral margin of fourth patch variably somewhat more dorsally positioned than dorsal margin of third patch; contralateral fourth patches in contact along dorsal midline and form saddle immediately anterior of adipose-fin base; fifth patch horizontally elongated and located entirely above lateral line; patch extends from vertical through middle of adipose fin to vertical through posterior extent of that fin; sixth patch horizontally elongated and of variable length on posterior half of caudal peduncle and terminates posteriorly at anterior limit of dark spot at caudal-fin base; dark spot at caudal-fin base semicircular; straight anteriorly and broadly convex posteriorly; spot extending nearly to dorsal and ventral margins of caudal peduncle; ventrolateral portion of abdomen and ventral part of caudal peduncle with scattered dark chromatophores; chromatophores absent on ventral portion of abdomen as far posterior as pelvic fin, even in darkly pigmented specimens; all branches of lateral-fin canal unpigmented (Ref. 88958). Dorsal and lateral portions of head dark brown other than variably shaped pale spot immediately posterior of eye; spot smaller than eye; ventral part of head unpigmented with distinct horizontal line between brown and pale portions ventrolaterally; maxillary barbel with dusky base dorsally, otherwise unpigmented; mandibular barbels unpigmented (Ref. 88958). Dorsal surfaces of pectoral and pelvic fins brown except for pale transverse patch extending across inner rays and pale distalmargin; ventral surface of pectoral and pelvic fins unpigmented except for small patch of dark chromatophores along basal portion of innermost rays; dark pigmentation on dorsal surface of distal portions of rays appears as dusky region extending along sub-marginal portion of ventral surface of both fins; dorsal fin with dense concentrations of dark chromatophores along rays; interradial membranes without chromatophores; adipose fin darkly pigmented, except for narrow pale distal margin on posterior one-half of fin; anal fin with dense concentrations of dark chromatophores along rays; interradial membranes without chromatophores; caudal fin with dense concentrations of dark chromatophores along rays; interradial membranes without chromatophores (Ref. 88958). In life the head is yellowish brown; the dark brownish dorsal regions are marked with 5-6 light spots, which are more or less confluent along the midline; the ventral region is bright orange; the lateral line is punctuated; the lower lobe of the caudal fin is darker; the fins have grayish margins and black bands; the external rays of the tail are gray-black; preserved specimens are dark brown, the ventral region is pale yellow (Ref. 88958).