Microsynodontis emarginatus, 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 : 15-19

Microsynodontis emarginatus sp. nov. ( Fig. 8 )

Type material. Holotype: CU 89393, male, 33.4 mm SL; Gabon: Haut­Ogooué Province, Motobo I village, Kiéne creek, 1°32'14.1"S 13°32'43.5"E; J. P. Sullivan et al., 12 August 1999.

Paratypes. CU 80567 (29), 8 females: 26.1–30.8 mm SL; 20 males: 23.4–33.6 mm SL; 1 unsexed: 19.5 mm SL; data as for holotype.

Diagnosis. Microsynodontis emarginatus can be distinguished from all congeners in having an emarginate (vs. rounded or truncate) caudal fin ( Fig. 9 ). It also exhibits no noticeable sexual dimorphism in the size and density of the tubercles on the dorsal and lateral surfaces of the head, unlike all other lower Guinea species of Microsynodontis .

Description. Biometric and meristic data as in Table 3 . 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 9–11, conical and separated from secondary teeth by distinct gap. Secondary teeth 35–50, acutely pointed and recurved; disposed in 3–4 rows. Tertiary teeth 15–24, elongate, villiform and extending over full width of premaxillae. Dentary teeth 15–21, 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,7 (30) 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 emarginate ( Fig. 10 a), with i,6,5,i (3) or i,6,6,i* (27) 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); iv,7* (22) or iv,8 (7) rays and convex margin. Pelvic­fin origin at vertical ventral to posterior end of dorsal­fin base. Pelvic fin with i,6 (30) rays and slightly convex margin; tip of appressed fin not reaching anal­fin origin. Pectoral fin with I,6 (30) rays; spine slightly curved and stout ( Fig. 4 c). Anterior spine margin with 15–22 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 13+22=35 (1); 12+24=36 (3); 13+23=36* (18); 13+24=37 (6); 14+22=36 (1) or 14+23=37 (1).

No marked sexual dimorphism in the size and density of tubercles on head. Males with long genital papilla situated immediately posterior to anus. Females 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. 8 ). 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 upper Ogooué River in southeastern Gabon ( Fig. 7 ).

Habitat. The type locality is a very slow­flowing creek. Water temperature was 25.4°C and the pH was 5.0. Syntopic fish included: Mormyridae : Brienomyrus spp., Marcusenius moorii , Mormyrops zanclirostris , Stomatorhinus walkeri ; Characidae : Brycinus sp.; Distichodontidae : Distichodus sp., Nannocharax sp.; Hepsetidae : Hepsetus odoe ; Cyprinidae : Barbus spp.; Amphiliidae : Amphilius nigricaudatus , Phractura sp., Clariidae : Clarias spp.; Claroteidae : Parauchenoglanis balayi ; Mochokidae : Synodontis sp.; Cyprinodontidae : Plataplochilus terveri ; Channidae : Parachanna insignis ; Cichlidae : Hemichromis sp.; Anabantidae : Ctenopoma kingsleyae ; Mastacembelidae : Caecomastacembelus sp.

Etymology. From the Latin emarginatus , meaning notched at the apex; in reference to distinctive shape of the caudal fin. 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 7. Map showing distributions of M. armatus (), M. emarginatus () and M. hirsutus ().

FIGURE 8. Microsynodontis emarginatus, holotype, CU 89393, 33.4 mm SL; Gabon: Ogooué River drainage.

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 10. Microsynodontis hirsutus, holotype, CU 87040, 68.0 mm SL; Gabon: Ntem River drainage.

Tables

TABLE 3. Biometric data for M. emarginatus (n = 30).

	HOLOTYPE	RANGE	MEAN±SD
SL (mm)	33.4	19.5–33.6
In % SL
Predorsal length	35.3	35.3–39.9	36.6±1.49
Snout to anal	68.8	66.5–71.9	68.7±1.74
Snout to pelvic	51.6	48.2–52.6	50.7±1.59
Snout to pectoral	20.3	19.9–24.7	22.4±1.63
Dorsal­fin base length	14.7	13.6–16.5	14.8±0.87
Dorsal spine length	17.2	16.8–19.9	18.0±1.25
Anal­fin base length	12.5	10.5–14.6	12.8±1.44
Pelvic­fin length	13.8	13.8–15.9	14.8±0.67
Pectoral fin length	24.1	21.6–25.1	23.3±1.22
Pectoral spine length	22.5	19.2–22.8	20.9±1.45
Caudal total length	22.5	21.4–25.8	23.7±1.64
Adipose basal length	28.1	27.9–30.2	28.7±0.79
Adipose maximum height	4.1	4.4–5.5	5.1±0.94
Dorsal to adipose distance	18.4	11.8–18.4	15.2±1.97
Adipose to caudal peduncle	8.4	8.4–12.5	10.3±1.35
Caudal peduncle length	16.3	16.1–19.3	17.7±1.31
Caudal peduncle depth	8.8	8.4–9.8	8.8±0.44
Body depth at anus	14.7	14.0–16.9	15.2±0.94
Head length	27.2	25.0–28.2	27.2±1.02
Head width	21.9	21.9–25.2	24.0±1.06
Head depth	16.9	16.2–19.2	17.5±0.93
In % HL
Snout length	42.5	41.4–47.9	44.8±2.59
Interorbital distance	36.8	34.0–41.2	37.0±2.24
Orbit diameter	21.8	17.8–21.2	19.2±1.04
Maxillary barbel length	98.9	91.8–109.5	102.8±6.92
Inner mandibular barbel length	55.2	44.1–59.5	55.4±5.01
Outer mandibular barbel length	74.7	68.8–85.3	75.5±5.21