Diagnosis: Congoglanis sagitta 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; a shallower caudal-peduncle depth, 6% of standard length vs. 7–8%; and more slender caudal peduncle, its depth 3.1–4.0 times in its length vs. 2.1–2.9; a shorter pelvic fin, 19–21% of standard length vs. 22–25%; a more anteriorly placed anal fin, its origin well in advance of tip of adpressed pelvic fin vs. origin approximately at tip of adpressed pelvic fin; 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; and more vertebrae, 39–41 vs. 35–37 (Ref. 88958). It differs from C. alula in having a shorter pectoral fin, 23–27% of standard length vs. 28–29%; a shorter pelvic fin, 19–21% of standard length vs. 24–28%; a longer caudal peduncle, 21–24% of standard length vs. 18–22%; and more slender caudal peduncle, its depth 3.1–4.0 times in its length vs. 2.6–3.3 times; a relatively wide interorbital width, 2 times eye diameter vs. 1.5 times; a more anteriorly placed anal fin, its origin well in advance of tip of adpressed pelvic fin vs. origin approximately at tip of adpressed pelvic fin; and more vertebrae, 39–41 vs. 36–39 (Ref. 88958).

Description: A slender species, with body very 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; 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 (Ref. 88958). Lateral line complete, running along midlateral surface of body (Ref. 88958). Caudal peduncle elongate, slender and compressed, but nearly as wide as high at terminus of anal-fin base; its length approximately equal to head length; least depth of caudal peduncle located approximately at posterior of peduncle (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 (Ref. 88958). Barbels tuberculate and distally tapered; maxillary barbel falling short of vertical through anterior margin of the 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 (Ref. 88958). Dorsal fin falcate, first branched ray longest, with i,6,i or i,7 rays; adipose fin located at vertical through anal-fin origin; pectoral fin large and falcate, with i,11, i,11,i or i,12 rays; pelvic fin with i,5 rays; anal fin small, with iv,5,i, iv,6, iv,6,i, iii,6,i or iii,7 rays; caudal fin deeply forked, asymmetrical, with ventral lobe longer and broader than dorsal lobe (Ref. 88958).

Colouration: Body coloration generally dark, with variable distinct lighter regions on overall dark brown body; body darker dorsally with brown coloration extending ventral of lateral line on abdomen and caudal peduncle; boundary between dark brown pigmentation of dorsal and dorsolateral regions and lighter coloration of ventrolateral and ventral regions relatively straight and horizontal from pectoral-fin base to caudal peduncle (Ref. 88958). Six pale patches distributed in irregular horizontal pattern along dorsolateral part of body (Ref. 88958).