Microsynodontis nasutus , Ng, Heok Hee, 2004

Ng, Heok Hee, 2004, The Microsynodontis (Teleostei: Siluriformes: Mochokidae) of the lower Guinea region, west central Africa, with the description of eight new species, Zootaxa 531, pp. 1-52: 32-35

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http://doi.org/ 10.5281/zenodo.157924

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Microsynodontis nasutus

sp. nov.

Microsynodontis nasutus  sp. nov. ( Fig. 14View FIGURE 14)

Type material. Holotype: CU 89394, male, 30.9 mm SL; Gabon: Woleu­Ntem province, Okano River on rapids 0.5 km S of village of Na, 0° 48 ' 35 "N 11 ° 38 ' 47 "E; C. D. Hopkins & M. E. Arnegard, 17 August 2001.

Paratypes. CU 86328 (7), 5 females: 26.6–36.5 mm SL; 2 males: 26.6–27.5 mm SL; data as for holotype.

Diagnosis. Microsynodontis nasutus  can be distinguished from all congeners in having a longer snout (50.0– 53.3 % HL vs. 35.7 –50.0).

Description. Biometric and meristic data as in Table 7. Body compressed. Predorsal profile gently convex; postdorsal body sloping gently ventrally. Preanal profile horizontal. Anus and urogenital openings located at vertical through middle of pelvic fin. Skin smooth. Lateral line complete and midlateral.

Head depressed and broad, broadly rounded when viewed laterally and with rounded snout margin when viewed from above. Gill openings narrow, extending from immediately ventral to posttemporal to immediately ventral to base of pectoral spine. Gill membranes united to, and attached across, isthmus. Bony elements of dorsal surface of head covered with thin skin. Nuchal shield large and terminating posteriorly with two rounded processes on each side. Supracleithral process thin, extending just short of vertical through posteriormost tip of nuchal shield.

Barbels in three pairs. Maxillary barbel long and slender, extending to just beyond base of last pectoral­fin ray. Inner mandibular­barbel origin close to midline, extending to base of pectoral spine and with 2 short, thin branches on anterior half and 3–5 long, thin branches on posterior half. Outer mandibular barbel originates posterolateral of inner mandibular barbel, extending to middle of pectoral­fin base and with 3–5 long, thin branches.

Eye ovoid, horizontal axis longest; located entirely in dorsal half of head. Orbit without free margin.

Mouth inferior and crescent­shaped; lips plicate. Oral teeth in rows on all tooth­bearing surfaces. Premaxillae narrow, with narrow ventral shelf and partially exposed when mouth closed. Primary teeth 11–12, conical and separated from secondary teeth by distinct gap. Secondary teeth 35–50, acutely pointed and recurved; disposed in 3–4 rows. Tertiary teeth 16–20, elongate, villiform and extending over full width of premaxillae. Dentary teeth 14–18, acutely pointed, strongly recurved and broader than secondary teeth; disposed in one or two transverse bands.

Dorsal fin located at anterior third of body, with II, 6,i* (6) or II, 7 (2) rays and convex margin. Dorsal­fin spine long, stout and slightly curved; smooth on both anterior and posterior margins. Adipose fin moderately long; margin slightly convex for entire length and posterior end deeply incised. Caudal fin rounded, with i,5,6,i (1); i,6,5,i (2) or i,6,6,i* (5) principal rays. Procurrent rays symmetrical and extend only slightly anterior to fin base. Anal­fin base located ventral to posterior half of adipose fin. Anal fin with iv, 6 * (2) or v, 6 (6) rays and convex margin. Pelvic­fin origin at vertical ventral to posterior end of dorsalfin base. Pelvic fin with i, 6 (8) rays and slightly convex margin; tip of appressed fin not reaching anal­fin origin. Pectoral fin with I, 6 (8) rays; spine slightly curved and stout (as in Fig. 4View FIGURE 4 f). Anterior spine margin with 16–22 small serrations along entire length of spine; serrations antrorse (distally directed) on distal two thirds and anteriorly directed on proximal third. Posterior spine margin with 7–9 strong serrations along entire length. Pectoralfin margin convex posteriorly. Vertebrae 11 + 25 = 36 (1) or 12 + 24 = 36 * (7).

Males with numerous tubercles on sides of head on region extending from snout to preopercle, and long genital papilla situated immediately posterior to anus. Females with fewer tubercles on sides of head, and with smaller, distally flattened genital papilla.

Coloration. In 70 % ethanol: dorsal and lateral surfaces and of head and body medium brown, fading to cream or light grayish brown on ventral third of body, belly (with large faint brown spots), and ventral surface of head ( Fig. 14View FIGURE 14). Snout with a series of cream spots delineating anterior and posterior nares, sometimes coalescing to form cream band running from anterior orbital margin to tip of snout. Cheek region with one or two cream spots immediately ventral to orbit. Cream band encircling nape at supraoccipital. Dorsal third of body with series of four cream vertical bar­shaped marks extending beyond lateral midline of body: first at middle of dorsal­fin base, second at adipose­fin origin, third at middle of adipose­fin base and last on caudal peduncle immediately posterior to adipose fin, sometimes encircling caudal peduncle as cream band. Ventral third of flanks with a longitudinal series of five to seven cream spots or vertical bar­shaped marks. Dorsal, pectoral, pelvic and anal fins hyaline and sometimes with one to two rows of faint spots forming longitudinal brown rows. Caudal fin with similar series of elongate marks forming two to three irregular columns.

Distribution. Known from the Okano River, a tributary of the Ogooué River, in northern Gabon ( Fig. 13View FIGURE 13).

Habitat. The type locality was a whitewater river, with the following fish found syntopically: Mormyridae  : Brienomyrus  spp.; Distichodontidae  : Distichodus hypostomatus  ; Cyprinidae  : Barbus martorelli  , Labeo  spp., Opsaridium ubangense  ; Amphiliidae  : Amphilius longirostris  , Amphilius nigricaudatus  , Doumea typica  , Phractura  sp.; Claroteidae  : Anaspidoglanis macrostoma  ; Mochokidae  : Atopochilus savorgnani  ; Cichlidae  : Hemichromis fasciatus  ; Mastacembelidae  : Caecomastacembelus niger  .

Etymology. From the Latin nasutus  , meaning large nosed; in reference to the long snout of this species. Used as a noun in apposition.

TABLE 7. Biometric data for M. nasutus (n = 8).

Outer mandibular barbel length