Chiloglanis orthodontus, Friel, John P. & Vigliotta, Thomas R., 2011
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publication ID |
https://doi.org/ 10.5281/zenodo.202193 |
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DOI |
https://doi.org/10.5281/zenodo.5632909 |
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persistent identifier |
https://treatment.plazi.org/id/9A2AC44D-FFA5-FFB8-FF21-FC62FC4BA666 |
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treatment provided by |
Plazi |
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scientific name |
Chiloglanis orthodontus |
| status |
sp. nov. |
Chiloglanis orthodontus View in CoL sp. nov.
( Figs. 1 View FIGURE 1 C & 5; Table 3 View TABLE 3 )
Holotype. CU 90567, 1 male ALC, 26.3 mm SL; Tanzania, Kigoma Region, side channel of Malagarasi River around island, 5.2005000°, S, 29.8987000° E; J.P. Friel & G. Kazumbe, 9 September 2004.
Paratypes. AMNH 251411, 15 ALC, 27.7–34.3 mm SL; Tanzania, Kigoma Region, Malagarasi River at rapids ~ 8 km down river of Igamba Falls, 5.1799300° S, 29.9803500° E; J.P. Friel, P.B. McIntyre & R.C. Schelly, 0 7 August 2009. — CU 90568, 1 female, 27.2 mm SL; Tanzania, Kigoma Region, Malagarasi River, at bridge between Kafura and Makere, 4.0257000°S, 30.5518000° E; J.P. Friel & S. Loader, 4 October 2004. — CU 94006, 9 male ALC, 18.4–28.7 mm SL, 4 female ALC, 21.1–22.4 mm SL; collection data as for holotype. — CU 95232, 15 ALC, 26.1-31.8 mm SL; same collection data as AMNH 251411. — MRAC 2010-006- P- 11-12, 2 ALC, 31.7– 32.6 mm SL; same collection data as AMNH 251411. — SAIAB 87165, 2 ALC, 29.9–32.6 mm SL; same collection data as AMNH 251411.
Non-type specimens. AMNH 251412, 1 ALC, 26.7 mm SL; Tanzania, Kigoma Region, Malagarasi River down river 4 km W from Uvinza at village of Nkwasa, 5.0979300° S, 30.3544900° E; J.P. Friel, P.B. McIntyre & R.C. Schelly, 11 August 2009. — AMNH 251413, 10 ALC, 24.2–33.1mm SL; Tanzania, Kigoma Region, Malagarasi River at rapids ~ 6.4 km upriver from Ilagala barge crossing, 5.2013400° S, 29.9001400° E; J.P. Friel, P.B. McIntyre & R.C. Schelly, 14 August 2009. — CU 90755, 4 male ALC, 26.0– 1.6 mm SL, 2 female ALC, 30.5– 3.2 mm SL, 1 undetermined gender C&S, 37.0 mm; Tanzania, Kigoma Region, Malagarasi River, 5.2010000° S, 29.9020000° E; J.P. Friel & G. Kazumbe, 9 September 2004. — CU 94104, 1 male ALC, SL unknown (damaged); same collection data as holotype. — CU 95233, 2 ALC, 22.2–33.7 mm SL; same collection data as AMNH 251412. — CU 95234, 11 ALC, 24.8–31.8 mm SL; same collection data as AMNH 251413.
Diagnosis. Chiloglanis orthodontus is a relatively small species (<30mm SL) 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 ( Figs. 1 View FIGURE 1 & 5 View FIGURE 5 ), and a very short dorsal spine (4.1–7.8% SL vs. always greater than 8.2%). This species is further distinguished from all Lake Tanganyika region species except C. productus , by a relatively long adipose fin (25.0–31.3% SL vs. <23.4% SL in all other Chiloglanis species except C. productus (22.5– 26.2% SL)).
Additional features useful for distinguishing this species from other species of Chiloglanis include a relatively small oral disc (width: 16.5–21.7% SL; length: 12.1–16.3% SL) with relatively elongate barbels (maxillary: 9.4– 14.8% SL; lateral mandibular: 3.8–10.7% SL; medial mandibular: 3.8–5.9% SL). 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 ( Fig. 1 View FIGURE 1 A&B), the dentary tooth cup of Vigliotta (2008). In C. orthodontus the dentary tooth cup is poorly developed ( Fig. 1 View FIGURE 1 C); 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 Daget & Stauch 1963 , known from the Volta and upper Bénoué River basins in western Africa, possesses a similar jaw morphology.
Description. Dorsal, lateral and ventral views in Figure 5 View FIGURE 5 illustrate body shape, form and position of fins and barbels. Morphometric and meristic data for holotype and 14 paratypes are summarized in Table 3 View TABLE 3 .
MERISTICS
Mandibular tooth rows 1* or 2 Mandibular tooth count (total) 11–20; 14* Mandibular tooth count (functional anterior row) 11–20; 14* Mandibular tooth count (posterior replacement row) -
Primary premaxillary teeth (total) 10–35; 24* Secondary premaxillary teeth (total) -
Tertiary premaxillary teeth (total) -
Pectoral-fin count I, 8*(15) Pelvic-fin count i, 6*(15) Dorsal-fin count II, 5*(15) Anal-fin count iii, 7*(10); iii, 6(5) Caudal-fin count i, 7, 8, i*(15) Pleural rib count (pairs) 6*(14); 7(1) Total vertebral count 32(3); 33(8); 34*(4)
Small species with maximum standard length <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 though origin of adipose fin. Skin fairly smooth. Lateral line complete and midlateral along side of body.
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.
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 medial mandibular barbels, somewhat more pronounced than medial mandibular barbels; primary barbel elongate and bordered medially by single short auxiliary barbel.
Premaxillae formed as block-like plates supporting 10–35‚“S”-shaped (in lateral view), 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 (in lateral view) 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 ( Fig. 1 View FIGURE 1 C).
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.
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 SL, 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 or 7. Pelvic-fin origin at vertical between bases of adipose and dorsal fin. Pelvic-fin margins convex, tip of appressed 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.
No apparent sexual dimorphism in shape or size of fins, body ornamentation, or tuberculation of skin.
Coloration. In 70% ethanol: General pigmentation of this species is shown in Figure 5 View FIGURE 5 . 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 colored 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 colored.
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.
Etymology. A combination of the Greek word orthos, meaning straight or erect, and the Greek word odontos, meaning tooth. This name refers to the mandibular dentition in this species, which is relatively straight and evenly spread across the dentary as compared to most other members of the genus. Used as a noun in apposition.
Distribution. Chiloglanis orthodontus sp. nov is known from several greatly separated sites in the lower Malagarasi River, and is likely endemic to the basin. It is most commonly encountered in small riffles, or in peripheral regions of rapids where the water velocity is much slower.
TABLE 3. Summary of morphometric measurements and meristic counts for Chiloglanis orthodontus sp. nov. (N = 15; holotype and 14 paratypes). Standard length expressed in mm. All other measurements expressed as % SL. Meristic data for holotype is identified by an asterisk, and the number of specimens with a particular value for fin rays, ribs and vertebrae is shown in parentheses.
| MORPHOMETRICS Standard length (mm) Head length | Holotype 26.3 28.5 | Range 18.4–28.7 25.3–33.6 | Mean±%SD 30.1±2.22 |
|---|---|---|---|
| Head depth (maximum) Body depth at anus | 14.1 14.8 | 14.0–19.9 13.7–17.4 | 15.8±1.74 14.9±0.89 |
| Occipital shield width (minimum) Prepectoral length Predorsal length Prepelvic length | 3.0 27.8 39.5 51.7 | 2.4–3.8 25.7–31.5 31.8–43.0 45.1–55.0 | 2.8±0.31 28.3±1.53 38.1±2.55 50.6±2.35 |
| Preanal length Eye diameter (horizontal) | 67.7 3.8 | 58.7–71.7 2.2–5.0 | 66.1±3.24 4.2±0.68 |
| Orbital interspace Snout length Premaxillary tooth-patch width Premaxillary tooth-patch length | 7.6 16.0 13.3 2.7 | 6.4–8.6 12.0–17.6 10.0–13.7 1.3–2.7 | 7.4±0.65 15.5±1.50 12.1±1.21 2.0±–0.39 |
| Mandibular tooth-row width Anterior nares interspace | 8.0 4.6 | 8.0–10.9 3.8–5.8 | 8.9±0.64 4.9±0.51 |
| Posterior nares interspace Maxillary barbel length Medial mandibular barbel length Lateral mandibular barbel length | 4.9 12.5 4.9 9.5 | 3.3–5.9 9.4–14.8 3.8–5.9 3.8–10.7 | 5.0±0.64 13.1±1.35 5.1±0.65 8.9±1.65 |
| Mouth width Oral disc width | 10.6 19.0 | 8.7–11.9 16.5–21.7 | 10.4±0.72 19.1±1.23 |
| Oral disc length Upper lip length Lower lip length Pectoral-spine length | 13.3 3.0 8.7 12.9 | 12.1–16.3 1.6–3.1 7.3–9.2 10.9–17.2 | 14.3±1.23 2.4±0.47 8.5±0.53 13.9±1.81 |
| Pectoral-fin length Width at pectoral-fin insertion | 17.9 25.9 | 14.1–20.1 23.9–27.8 | 17.2±1.61 25.8±0.99 |
| Length of postcleithral process | - | - | - continued next page |
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