| Diagnosis: |
Dorsal spines (total): 2-2; Dorsal soft rays (total): 5-6; Anal spines: 0-0; Anal soft rays: 9-11; Vertebrae: 33-33. Diagnosis: Chiloglanis igamba is a sexually dimorphic species in which the caudal fin of adult males is relatively truncate, but with the middlemost rays moderately elongated; females and juvenile males of this species in contrast exhibit a gently forked caudal fin; sexual dimorphism of the caudal fin is also apparent in several other species of Chiloglanis, including the following from various tributaries flowing into Lake Tanganyika: C. trilobatus, C. kalambo, C. productus and C. asymetricaudalis, but the particular shape of the caudal fin in C. igamba is unique among all congeners (Ref. 87986). The most similar sexually dimorphic caudal fins are found in males of C. trilobatus and C. kalambo, where the middle most rays form a third lobe; the trilobate caudal-fin shape in these species can be distinguished from the shape in C. igamba by the areas between upper, middle and lower lobes, which are notably recessed; in C. igamba these recessed areas are absent and clearly trilobate shape is not evident; Chiloglanis igamba is further distinguished from C. trilobatus and C. kalambo by a shorter adipose-fin length, 10.3-16.3% of standard length vs. 16.4-22.3% in C. trilobatus and 16.5-23.4% in C. kalambo; a shorter depth at dorsal fin insertion, 14.5-18.4% of standard length vs. 20.0-24.0% in C. trilobatus and 18.2-23.5% in C. kalambo; a shorter caudal peduncle depth, 8.7-12.6% of standard length vs. 11.9-14.5% in C. trilobatus and 11.3-15.4% in C. kalambo; a longer snout length, 20.3-26.2% of standard length vs. mean of 19.9% in C. trilobatus and mean of 18.4% in C. kalambo; a shorter maxillary barbel, 5.0-7.5% of standard length vs. a mean of 10.6% in C. trilobatus and mean of 9.3% in C. kalambo; a wider oral disc, 20.4-26.8% of standard length vs. mean of 19.0% in C. trilobatus and mean of 19.7% in C. kalambo; a wider set of premaxillary tooth plates, 15.6-19.8% of standard length vs. mean of 14.0% in C. trilobatus and mean of 13.7% in C. kalambo; 27-45 primary teeth on each premaxilla, vs. 18-31 in C. trilobatus and 7-21 in C. kalambo; 6 soft rays in the dorsal fin, rarely 5, vs. 5 rays in C. trilobatus and C. kalambo (Ref. 87986). Caudal-fin shape in males of C. igamba is also fairly similar to the shape found in males of C. productus; but in C. productus all caudal-fin rays, especially the middle rays, are elongated and the fin is diamond shaped; Chiloglanis igamba is also easily distinguished from C. productus by its pigmentation, which consists of cream-coloured splotches on a light brown background; in contrast, the pigmentation of C. productus is medium to dark brown with a pale midlateral stripe along the lateral line; Chiloglanis igamba is further distinguished from C. productus by a shorter pectoral spine, 9.9-15.1% of standard length vs. 15.2-18.5%; a shorter pectoral-fin longest ray, 15.2-18.8% of standard length vs. 19.1-23.9%; and a shorter adipose-fin base, 10.3-16.3% of standard length vs. 22.5-26.2% (Ref. 87986). Finally, in Chiloglanis asymetricaudalis the caudal fin of adult males is forked, but with an elongate upper lobe; in addition to caudal fin shape, C. igamba is easily distinguished from C. asymetricaudalis by a shorter pectoral spine, 9.9-15.1% of standard length vs. 16.4-19.7%; a shorter dorsal spine, 8.2-12.7% of standard length vs. 13.0-15.7%; a shorter anal fin, 11.7-15.9% of standard length vs. 22.6-28.0%; a shorter caudal peduncle, 15.0-17.7% of standard length vs. 18.4-20.9%; and a markedly different pigment pattern (Ref. 87986).
Description: Moderately sized Chiloglanis species, maximum standard length less than 70 mm; body roughly cylindrical, depressed anteriorly and compressed posteriorly; predorsal profile convex; postdorsal body sloping gently ventrally; preanal profile horizontal; anus and urogenital opening located at vertical through origin of adipose fin; skin with numerous small unculiferous tubercles, especially towards head and along dorsal midline; lateral line complete and midlateral along side of body (Ref. 87986). Head depressed and broad, snout margin rounded when viewed dorsally; gill opening restricted to lateral aspect of head from level of base of pectoral spine to level of middle of eye; gill membranes broadly united to, and attached across isthmus, supported by 5 or 6 branchiostegal rays; bony elements of skull roof lack any superficial ornamentation; skin covering skull roof with numerous small, round unculiferous tubercles; occipital-nuchal shield small, not visible through skin dorsally (Ref. 87986). Mouth inferior, lips form ventrally-directed oral disc; oral disc quite large, nearly as wide as head and covered by numerous papillae; posterior margin of oral disc with well-developed cleft present at midline; barbels in three pairs; maxillary barbel short, thick and unbranched, about as long as diameter of eye; emanating from posterolateral region of oral disc; mandibular barbels incorporated into lower lip and visible as trifurcate structures in cleared and stained specimens; medial mandibular barbels on each side of midline; primary and auxiliary barbels visible as three small bumps in lower lip margin; lateral mandibular barbels just lateral to medial mandibular barbels, somewhat more pronounced; primary and auxiliary barbels visible as three small bumps in lower lip margin; middle of tips presenting as short pointed barbel, one half length of maxillary barbel (Ref. 87986). Premaxillae formed as claw-shaped plates supporting 57-89, 'S'-shaped, pointed primary teeth distributed in oval patches on ventral surface; 20-40 smaller secondary teeth on posterior surface of premaxillae; 8-16 needle-like teeth inserting above and behind secondary teeth towards roof of mouth and gathered at midline; number of premaxillary teeth increases with overall body size; dentary with well-formed tooth cup along anterior margin supporting one or two rows of 7 or 8 robust, 'S'-shaped teeth with pointed tips; when present, posterior row represents replacement teeth; mandibular teeth bunched at midline (Ref. 87986). Eyes small and ovoid, horizontal axis slightly longer than vertical axis; less than one third of orbital interspace; orbit without free margin; anterior nares and posterior nares equidistant; anterior nares tubular with short, raised rim; posterior nares with elevated flaps along anterior margin (Ref. 87986). Dorsal fin located at anterior third of body; dorsal fin with spinelet, spine and 5-6 rays; fin membrane not adnate with body; dorsal-fin spine short and straight, between 2 or 3 times as long as diameter of eye; smooth along anterior and posterior margins; adipose fin short, base up to one sixth of standard length, originating near posterior third of body; margin convex and deeply incised posteriorly; caudal fin sexually dimorphic, shallowly forked in females and trilobate in males, middle rays elongated; caudal fin with i,7,8,i rays; procurrent caudal-fin rays symmetrical and extending only slightly anterior to fin base; anal-fin base located ventral to adipose-fin base; margin convex; anal-fin count iii,6-8; pelvic-fin origin at vertical between bases of adipose and dorsal fin; pelvic-fin margins convex, tip of adpressed fin just reaching anal-fin origin; pelvic-fin count i,6; pectoral fin with slightly curved, short, stout spine; anterior and posterior spine margins smooth; pectoral fin count I,8-9; cleithral processes short and obtusely pointed, largely buried in skin; very small axillary pore present, but may be difficult to see or obscured by cleithral process in some specimens (Ref. 87986).
Colouration: In ethanol, in dorsal view, specimens appear medium brown, with indistinct lighter bands or rows of spots posterior to head; most well-formed bands between dorsal and adipose fins and at terminus of adipose fin; head uniformly light to medium brown; in lateral view, specimens appear mostly medium brown with lighter abdomen and numerous lighter spots; above lateral line, small spots in 6 or 7 evenly spaced vertical rows, corresponding to free neuromasts; spots slightly enlarged between bases of dorsal and adipose fin bases and at terminus of adipose fin; lateral line with tiny lighter spots corresponding to pores; below lateral line, large light spots at anal fin origin and below terminus of adipose fin; ventral surface cream coloured with some spots of dark pigment from origin of pelvic fins to end of anal-fin base; oral disc, all barbels, anus and urogenital opening cream coloured; dorsal and pectoral spines and rays light brown; base of dorsal and pectoral-fin rays generally darker; fin membranes nearly translucent; pelvic and anal fins milky-white; base of anal-fin rays darker or cream coloured; adipose fin with medium brown base and translucent milky-white posterodorsal margin; base of caudal-fin rays dark; wide band of darker pigment along middle of rays separated from dark basal colour by cream-coloured patch; tips generally cream coloured (Ref. 87986). |