Microsynodontis laevigatus, 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 : 24-27

Microsynodontis laevigatus sp. nov. ( Fig. 11 )

Type material: Holotype: CU 89407, male, 30.8 mm SL; Gabon: Ogooué­Ivindo province, Ivindo River drainage, small creek flowing into Ivindo River, Makokou, 0°35'8"N 12°51'22"E; J. P. Friel, S. Lavoué & J. P. Sullivan, 6 September 2002.

Paratypes: CU 88265 (13), 5 females: 21.5–24.5 mm SL; 8 males: 20.5–28.1 mm SL; data as for holotype.

Diagnosis. Microsynodontis laevigatus can be distinguished from all congeners (except for M. lamberti ) in having a smooth (vs. serrated) anterior edge of the pectoral spine ( Fig. 4 ), and a truncate (vs. emarginate or rounded) caudal fin ( Fig. 9 ). It differs from M. lamberti (n=4) in having a longer adipose fin (33.3–35.5% SL vs. 25.4–31.4).

Description. Biometric and meristic data as in Table 5 . Body compressed. Predorsal profile steep; 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 3–4 long, thin branches on posterior half. Outer mandibular barbel originates posterolateral of inner mandibular barbel, extending to middle of pectoral­fin base and with 3–4 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 10–14, conical and separated from secondary teeth by distinct gap. Secondary teeth 30–40, acutely pointed and recurved; disposed in 3–4 rows. Tertiary teeth 18–21, elongate, villiform and extending over full width of premaxillae. Dentary teeth 12–20, 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,4,i (1); II,5,i (9) or II,6* (4) rays and convex margin. Dorsal­fin spine short, 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 truncate, with i,6,5,i (14) 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 (1) or iv,7* (13) rays and convex margin. Pelvic­fin origin at vertical ventral to posterior end of dorsal­fin base. Pelvic fin with i,6 (14) rays and slightly convex margin; tip of appressed fin not reaching anal­fin origin. Pectoral fin with I,5,i (14) rays; spine slightly curved and stout ( Fig. 4 d). Anterior spine margin smooth along entire length of spine. Posterior spine margin with 7–8 strong serrations along entire length. Pectoral­fin margin convex posteriorly. Vertebrae 11+22 (2); 11+23 (1); 12+22 (6); 12+23 (3) or 13+22* (2).

HOLOTYPE RANGE MEAN ±SD

SL (mm) 30.8 20.5–30.8

In % SL

Maxillary barbel length 139.8 98.7–139.8 121.0±14.2

Inner mandibular barbel length 54.2 54.2–78.2 66.1±9.16 Outer mandibular barbel length 97.6 75.6–120.5 120.5±13.43 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 on belly and ventral surfaces ( Fig. 11 ). Medium­sized brown spots evenly scattered over ventral surfaces. 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 numerous small cream spots ventral and posterior to orbit. Cream band encircling nape at supraoccipital. Dorsal third of body with series of four cream irregular blotches extending short of 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 coalescing with similar marks ventrally and encircling caudal peduncle as irregular cream band. Ventral third of flanks with a series of irregular cream blotches sometimes coalescent with dorsal markings to form reticulate pattern. Dorsal, pectoral, pelvic and anal fins hyaline and sometimes with one to two rows of faint spots forming longitudinal brown rows. Caudal fin hyaline, with elongate brown spots forming two to three irregular columns.

Distribution. Known only from the Ivindo River in northern Gabon ( Fig. 5 ).

Habitat. The type locality is a small, shallow blackwater creek draining into the Ivindo River. The water was extremely low and the substrate was sand with leaf litter, with the area having undergone severe human disturbance. The only other fish species found syntopically was Barbus sp. ( Cyprinidae ).

Etymology. From the Latin laevigatus , meaning smooth. In reference to the smooth anterior edge of the pectoral spine. Used as an adjective.

Figures

FIGURE 4. Dorsal view of pectoral spines of: a. M. armatus, holotype, CU 89392, 27.4 mm SL; b. M. christyi, MRAC 61801, 37.5 mm SL; c. M. emarginatus, paratype, CU 80567, 32.0 mm SL; d. M. laevigatus, paratype, CU 88265, 28.1 mm SL; e. M. notatus, holotype, MRAC 80 ­ 51 ­ P­ 839, 41.0 mm SL; f. all other Microsynodontis (represented by M. batesii, MRAC 93 ­ 085 ­ P­ 0280, 42.6 mm SL). Scale bar represents 1 mm.

FIGURE 5. Map showing the distribution of M. batesii (), M. laevigatus () and M. notatus ().

FIGURE 9. Lateral view of caudal fins showing: a. emarginate fin (condition in Microsynodontis emarginatus, CU 89393, holotype, 33.4 mm SL); b. rounded fin (other Microsynodontis species, represented by M. batesii, CU 80748, 33.2 mm SL); c. truncate fin (condition in M. laevigatus and M. lamberti, represented by M. laevigatus, CU 88265, paratype, 22.8 mm SL).

FIGURE 11. Microsynodontis laevigatus, holotype, CU 89407, 30.8 mm SL; Gabon: Ivindo River drainage.

Tables

TABLE 5. Biometric data for M. laevigatus (n = 14).

Predorsal length	36.7	34.8–39.1	37.1±1.51
Snout to anal	65.3	64.1–71.0	66.8±2.37
Snout to pelvic	45.5	45.5–53.1	49.1±2.31
Snout to pectoral	25.6	22.8–25.6	23.8±0.91
Dorsal­fin base length	13	12.1–16.1	13.6±1.32
Dorsal spine length	14.9	13.5–17.1	15.3±1.18
Anal­fin base length	14	12.7–17.1	14.8±1.53
Pelvic­fin length	14.9	14.9–17.6	16.4±1.08
Pectoral fin length	23.7	20.1–25.3	23.2±1.68
Pectoral spine length	17.9	16.7–21.8	19.6±2.05
Caudal total length	24.4	24.3–28.5	25.9±1.48
Adipose basal length	35.1	33.3–35.5	34.6±0.93
Adipose maximum height	6.2	4.0–6.2	5.3±0.69
Dorsal to adipose distance	10.4	10.2–12.5	11.3±0.93
Adipose to caudal peduncle	9.7	8.6–10.1	9.6±0.51
Caudal peduncle length	16.6	15.7–19.5	17.2±1.47
Caudal peduncle depth	11	9.3–11.4	10.7±0.74
Body depth at anus	20.1	18.9–22.1	20.3±1.01
Head length	26.9	26.9–30.7	28.5±1.29
Head width	24	24.0–26.9	25.4±1.05
Head depth	20.1	19.2–21.7	20.1±0.93
In % HL
Snout length	43.4	39.0–45.7	43.0±2.40
Interorbital distance	39.8	35.1–39.8	37.3±1.71
Orbit diameter	18.1	15.6–21.8	18.2±2.45