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Dorsal spines (total): 2-2; Dorsal soft rays (total): 5-5; Anal spines: 0-0; Anal soft rays: 9-10; Vertebrae: 32-34. Diagnosis: Chiloglanis orthodontus is a relatively small species, less than 30 mm standard length, that can be distinguished from all other Malagarasi congeners by possessing dentary teeth spread out across the mouth opening as opposed to being concentrated at the midline, and a very short dorsal spine, 4.1–7.8% of standard length vs. always greater than 8.2% (Ref. 87986). This species is further distinguished from all Lake Tanganyika region species except C. productus, by a relatively long adipose fin, 25.0–31.3% of standard length vs. less than 23.4% in all other Chiloglanis species except C. productus, which has 22.5– 26.2% (Ref. 87986). Additional features useful for distinguishing this species from other species of Chiloglanis include a relatively small oral disc, width 16.5-21.7% of standard length and length 12.1-16.3% of standard length, with relatively elongate barbels, maxillary barbel 9.4-14.8% of standard length, lateral mandibular barbel 3.8-10.7% of standard length, medial mandibular barbel 3.8-5.9% of standard length (Ref. 87986). These features and the widely spaced teeth of the lower jaw are associated with another distinctive character in this species: the shape of the lower jaw; in most species of Chiloglanis the lower jaw is similar to that found in species of Synodontis, where elongate 'S'-shaped teeth insert in a cavity on the anterior side of the dentary; in C. orthodontus the dentary tooth cup is poorly developed; the dentary teeth project from the anterodorsal surface of the dentary and are only very gently 'S'-shaped; thus far among Chiloglanis species, only Chiloglanis voltae, known from the Volta and upper Bénoué River basins in western Africa, possesses a similar jaw morphology (Ref. 87986).
Description: Small species with maximum standard length less than 30 mm; body roughly cylindrical, depressed anteriorly and compressed posteriorly; predorsal profile gently convex; postdorsal body sloping gently ventrally; preanal profile horizontal; anus and urogenital opening located at vertical through origin of adipose fin; skin fairly smooth; 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 ventral margin of eye; gill membranes broadly united to, and attached across isthmus, supported by 7 branchiostegal rays; bony elements of skull roof lack any superficial ornamentation; skin covering skull roof relatively smooth; occipital-nuchal shield small, not visible through skin dorsally (Ref. 87986). Mouth inferior, lips form ventrally-directed oral disc; oral disc small, wider than long and covered by numerous indistinct papillae; posterior margin of oral disc with well-developed cleft present at midline; barbels in three pairs and well developed; maxillary barbel slender and unbranched, originating just anterior to widest point of oral disc and extending to just beyond united gill membranes; short basal membrane present on maxillary barbel; 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 barbel elongate and bordered by short auxiliary barbel on each side; lateral mandibular barbels just lateral to median mandibular barbels, somewhat more pronounced than medial mandibular barbels; primary barbel elongate and bordered medially by single short auxiliary barbel (Ref. 87986). Premaxillae formed as block-like plates supporting 10-35, 'S'-shaped, pointed primary teeth on ventral surface; secondary teeth on posterior surface of premaxillae, very small and difficult to accurately count; tertiary teeth not obviously differentiated from secondary teeth; increased numbers of premaxillary teeth in larger specimens; dentary with poorly formed anterodorsally directed tooth cup supporting 11-20, gently 'S'-shaped teeth with pointed tips; cleared and stained specimens reveal a poorly defined posterior row of small replacement teeth that are difficult to count accurately in intact specimens; mandibular teeth, in general, are arranged relatively loosely along dentary, rather than distinctly concentrated at midline (Ref. 87986). Eyes small and ovoid, horizontal axis slightly longer than vertical axis; approximately one half 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 rays; fin membrane not adnate with body; dorsal-fin spine very short and straight, scarcely longer than diameter of eye; smooth along anterior and posterior margins; adipose fin very long, base up to one third of standard length, originating at second half of body; margin gently convex and deeply incised posteriorly; caudal fin gently forked; count i,7,8,i; procurrent caudal-fin rays symmetrical and extending only slightly anterior to fin base; anal-fin base located ventral to adipose-fin base, but much shorter; margin convex; anal-fin count iii,6-7; pelvic-fin origin at vertical between bases of adipose and dorsal fin; pelvic-fin margins convex, tip of adpressed fin just short of anal-fin origin; pelvic-fin count i,6; pectoral fin with straight, stout spine; anterior and posterior spine margins smooth; pectoral fin count I,8; cleithral process altogether absent; no obvious axillary pore present (Ref. 87986).
Colouration: In ethanol, in dorsal view, specimens appear medium brown, with two lighter bands or rows of spots on posterior half of body; first band lies at origin of adipose fin and second band lies at terminus of adipose fin; head light to medium brown, darkest between eyes; in lateral view, specimens appear mostly medium brown with lighter abdomen and set of lighter spots; lighter spot at origin of adipose fin, above lateral line only and separated from dorsal spot by thin line of pigment; lighter spot at terminus of adipose fin continuous with dorsal spot, extending more or less to ventral midline, but with notable pigmentation along lateral line; additional lighter spot present below lateral line at origin of anal 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 translucent milky-white; base of dorsal and pectoral-fin rays generally darker; fin membranes translucent; pelvic and anal fins milky-white; base of anal-fin rays darker; adipose fin with very dark base and translucent milky-white posterodorsal margin; base of caudal-fin rays very dark; wavy band of dark pigment towards tips of rays; barbell-shaped milky-white spot inbetween (Ref. 87986). |