Microsynodontis hirsutus, 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 : 20-23

Microsynodontis hirsutus sp. nov. ( Fig. 10 )

Type material. Holotype: CU 87040, male, 68.0 mm SL; Gabon: Woleu­Ntem province, Ngomo creek, where it crosses Oyem­Minvoul road, 1°41'30.0"N 11°39'18.9"E; J. P. Friel, S. Lavoué & J. P. Sullivan, 11 September 1999.

Paratypes. CU 80584 (3), 2 females: 25.7–26.5 mm SL; 1 male: 28.0 mm SL; data as for holotype.

Diagnosis. Microsynodontis hirsutus can be distinguished from all congeners in having long (vs. short) tubercles on the dorsal and lateral surfaces of the head ( Fig. 3 ) and a straight (vs. gently curved) dorsal spine ( Fig. 2 ). The tubercles are typically 0.3 mm long in the holotype of M. hirsutus , while in similar­sized specimens of other Microsynodontis , they are about 0.05 mm long; the smaller paratype male of M. hirsutus (28.0 mm SL) has tubercles 0.1 mm long, as compared to 0.05 mm in other male congeners of similar size. The tubercles are 0.05 mm in the larger paratype female, as compared to 0.02 mm in female congeners of the same size. It further differs from congeners except M. batesii and M. polli in having a longer adipose fin (34.6–37.9% SL vs. 21.3–35.5). It can be further distinguished from M. polli (n=9) in having a shorter caudal fin (20.0–24.3% SL vs. 29.6– 41.6).

Description. Biometric and meristic data as in Table 4 . 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, acutely 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 14–21, conical and separated from secondary teeth by distinct gap. Secondary teeth 40–85, acutely pointed and recurved; disposed in 3–4 rows. Tertiary teeth 19–28, elongate, villiform and extending over full width of premaxillae. Dentary teeth 17–25, 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 (4) rays and convex margin. Dorsal­fin spine long, stout and straight; smooth on both anterior and posterior margins. Adipose fin long, extending for most of postdorsal distance; margin slightly convex for entire length and posterior end deeply incised. Caudal fin rounded, with i,6,6,i (4) 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* (2) or iv,8 (2) rays and convex margin. Pelvic­fin origin at vertical ventral to posterior end of dorsal­fin base. Pelvic fin with i,6 (4) rays and slightly convex margin; tip of appressed fin not reaching anal­fin origin. Pectoral fin with I,6 (4) rays; spine slightly curved and stout (as in Fig. 4 f). Anterior spine margin with 12–35 small serrations along entire length of spine; serrations antrorse (distally directed) on distal two­thirds and anteriorly directed on proximal third. Posterior spine margin with 9–13 strong serrations along entire length. Pectoral­fin margin convex posteriorly. Vertebrae 12+24* (3) or 13+24 (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 (adults larger than ca. 30 mm SL): dorsal and lateral surfaces and of head and body brownish gray, fading to dirty cream on ventral third of body, belly (with faint traces of brownish gray spots), and ventral surface of head ( Fig. 10 ). Snout with a series of cream spots delineating anterior and posterior nares. 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 six to eight cream spots or vertical barshaped marks. Pectoral and pelvic fin rays with brownish gray spots arranged in two or three bands. Dorsal­, anal­ and caudal­fin rays brownish gray, with hyaline interradial membranes.

Coloration of juveniles (smaller than ca. 30 mm SL) similar, except for being more brown than gray dorsally, a cream belly with brown spotting on posterior half (vs. spotting almost indistinct in adults), and dorsal­, anal­ and caudal­fin rays with brown spots arranged into one or two bands (coalescing to give solidly­colored fin rays in adults).

Distribution. Known from the Nyé River (a tributary of the Ntem River) in northern Gabon ( Fig. 7 ).

Habitat. The type locality was a fast­flowing creek over a rock/pebble substrate. The water was cool (22°C), acidic ( pH 5.0) and tannin­stained. Syntopic fish included: Mormyridae : Brienomyrus sp.; Distichodontidae : Distichodus sp.; Cyprinidae : Barbus spp.; Amphiliidae : Amphilius longirostris ; Clariidae : Clarias jaensis ; Mochokidae : Chiloglanis cameronensis ; Mastacembelidae : Aethiomastacembelus sp.

Etymology. From the Latin hirsutus , meaning hairy; in reference to the long tubercles on the dorsal and lateral surfaces of the head, which gives the species a somewhat hairy appearance of the head. Used as an adjective.

Figures

FIGURE 2. Lateral view of dorsal spines of: a. M. hirsutus, holotype, CU 87040, 62.0 mm SL and b. all other Microsynodontis (represented by M. batesii, CAS 155691, 62.4 mm SL). Scale bar represents 1 mm.

FIGURE 3. Magnified view of the right ventrorbital region, showing tubercle morphology in mature males of: a. M. hirsutus, holotype, CU 87040, 62.0 mm SL; and b. all other Microsynodontis (represented by M. batesii, RMNH 34859, 74.8 mm SL). Both photographs were taken under identical magnification (50 X). Scale bar indicates 0.5 mm.

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

Tables

TABLE 4. Biometric data for M. hirsutus (n = 4).

	HOLOTYPE	RANGE	MEAN±SD
SL (mm)	68.0	25.7–68.0
In % SL
Predorsal length	32.9	32.9–38.5	36.6±2.57
Snout to anal	63.2	63.2–70.0	66.1±3.34
Snout to pelvic	45.9	44.5–49.3	46.5±2.02
Snout to pectoral	19.7	19.7–23.4	22.0±1.64
Dorsal­fin base length	13.1	11.7–13.6	13.0±0.90
Dorsal spine length	17.1	17.1–19.5	18.0±1.14
Anal­fin base length	15.0	12.5–15.0	14.0±1.21
Pelvic­fin length	12.9	12.9–15.4	14.5±1.08
Pectoral fin length	22.1	22.1–26.8	24.7±2.03
Pectoral spine length	19.3	19.1–23.2	20.9±2.00
Caudal total length	24.4	20.0–24.3	22.3±2.35
Adipose basal length	37.9	34.6–37.9	36.1±1.37
Adipose maximum height	6.0	3.9–6.0	5.1±0.94
Dorsal to adipose distance	10.9	10.9–14.3	12.1±1.60
Adipose to caudal peduncle	7.6	5.7–7.6	7.0±0.86
Caudal peduncle length	18.7	12.9–18.7	15.0±2.59
Caudal peduncle depth	7.2	7.1–7.8	7.3±0.32
Body depth at anus	14.3	11.7–15.0	13.9±1.51
Head length	24.1	24.1–26.8	25.6±1.16
Head width	20.3	20.3–25.4	22.6±2.42
Head depth	14.1	14.1–15.6	15.2±0.70
In % HL
Snout length	45.7	41.8–46.3	44.5±2.02
Interorbital distance	31.1	31.1–43.3	38.0±5.07
Orbit diameter	17.0	16.0–17.0	16.5±0.41
Maxillary barbel length	100.6	100.0–126.9	112.5±14.18
Inner mandibular barbel length	61.0	46.3–68.0	58.8±9.07
Outer mandibular barbel length	95.1	81.3–95.1	88.9±8.33