Microsynodontis armatus, 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 : 10-15

Microsynodontis armatus sp. nov. ( Fig. 6 )

Type material: Holotype: CU 89392, male, 27.4 mm SL; Gabon: Ogooué­Ivindo province, Ivindo River drainage, Balé Creek, 0°31'9"N 12°47'58"E; C. D. Hopkins et al., 24 August 2001.

Paratypes: CU 86327 (2), 1 female: 26.6 mm SL; 1 unsexed: 19.7 mm SL; data as for holotype.

Diagnosis. Microsynodontis armatus can be distinguished from all congeners in having retrorse (proximally directed) serrations (vs. smooth or with either anteriorly directed or antrorse (distally directed) serrations) along the proximal third of the anterior edge of the pectoral spine ( Fig. 4 a).

HOLOTYPE RANGE MEAN ±SD

SL (mm) 27.4 19.7–27.4

In % SL

Maxillary barbel length 94.4 94.4–113.2 103.8±13.29 Inner mandibular barbel length 45.8 45.6–45.8 45.7±0.14 Outer mandibular barbel length 56.9 56.9–92.6 74.8±25.24

Description. Biometric and meristic data as in Table 2 . 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 3–4 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 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,5,i (2) or II,6* (1) 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 rounded, with i,6,5,i (3) 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,7 (3) rays and convex margin. Pelvic­fin origin at vertical ventral to posterior end of dorsal­fin base. Pelvic fin with i,6 (3) rays and slightly convex margin; tip of appressed fin not reaching anal­fin origin. Pectoral fin with I,6 (3) rays; spine slightly curved and stout ( Fig. 4 a). Anterior spine margin with 21–27 small serrations along entire length of spine; serrations antrorse (distally directed) on distal two­thirds and retrorse (proximally directed) on proximal third. Posterior spine margin with 6–12 strong serrations along entire length. Pectoral­fin margin convex posteriorly. Vertebrae 12+22=34 (1); 13+21=34 (1) or 12+23=35 (1).

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. 6 ). 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 with similar series of elongate marks forming two to three irregular columns.

Distribution. Known only from the Ivindo River in northern Gabon ( Fig. 7 ).

Habitat. The type locality is a blackwater forest stream with sand and leaf litter bottom. Water temperature was 22.0°C and the pH was 5.0. Syntopic fish included: Mormyridae : Brienomyrus spp., Isichthys henryi , Marcusenius moorii , Mormyrops zanclirostris , Petrocephalus christyi , Characidae : Brycinus kingsleyae ; Distichodontidae : Distichodus notospilus , Nannocharax fasciatus ; Cyprinidae : Barbus spp., Opsaridium ubangense , Raiamas buchholzi , Clariidae : Clarias sp.; Claroteidae : Parauchenoglanis balayi ; Schilbeidae : Schilbe laticeps ; Mochokidae : Synodontis batesii ; Cichlidae : Hemichromis fasciatus , Parananochromis sp., Tilapia sp.

Etymology. From the Latin armatus , meaning armed. In allusion to the antrorse (distally directed) and retrorse (proximally directed) serrations on the anterior edge of the pectoral spine unique to this species. Used as a noun in apposition.

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 6. Microsynodontis armatus, holotype, CU 89392, 27.4 mm SL; Gabon: Ivindo River drainage.

FIGURE 7. Map showing distributions of M. armatus (), M. emarginatus () and M. hirsutus ().

Tables

TABLE 2. Biometric data for M. armatus (n = 3).

Predorsal length	36.9	36.9–39.6	38.3±1.35
Snout to anal	67.5	67.5–71.1	68.6±2.02
Snout to pelvic	49.6	49.2–50.0	49.6±0.40
Snout to pectoral	20.1	19.9–20.8	20.3±0.47
Dorsal­fin base length	14.6	10.2–14.6	12.2±2.24
Dorsal spine length	16.4	16.4–20.3	18.5±1.97
Anal­fin base length	14.6	11.2–16.5	14.1±2.69
Pelvic­fin length	13.1	13.1–16.9	15.6±2.17
Pectoral fin length	23.7	23.7–30.5	26.6±3.51
Pectoral spine length	21.9	21.9–24.9	23.1±1.57
Caudal total length	28.1	20.8–28.1	24.4±3.65
Adipose basal length	32.1	25.9–32.9	28.4±3.29
Adipose maximum height	2.6	2.6–3.5	3.0±0.45
Dorsal to adipose distance	19.3	17.3–19.3	18.6±1.15
Adipose to caudal peduncle	8.0	7.9–8.1	8.0±0.10
Caudal peduncle length	20.1	11.2–20.1	15.4±4.47
Caudal peduncle depth	9.1	8.3–9.1	8.7±0.40
Body depth at anus	13.9	13.7–15.0	14.2±0.70
Head length	26.3	25.6–26.3	25.9±0.35
Head width	22.3	22.3–25.4	24.0±1.58
Head depth	15.7	15.7–17.7	16.7±1.00
In % HL
Snout length	43.1	43.1–48.5	44.9±3.12
Interorbital distance	37.5	37.5–45.1	41.2±3.80
Orbit diameter	13.9	13.9–16.7	15.6±1.49