Phenacogrammus concolor, new species

Figures 1, 6; table 5

HOLOTYPE: AMNH 274786, 43.9 mm SL, Democratic Republic of Congo, Mai-Ndombe Province, Ndzaa River (02° 58′ 25.0″8S 018° 7′ 55.26″E), R. Monsembula Iyaba et al., 25 July 2018.

PARATYPES: AMNH 276321, 4 specimens, 2 CT-scanned, 42.9– 34.5 mm SL, same data as holotype.

DIFFERENTIAL DIAGNOSIS: While no unambiguous morphological autapomorphies have been located to diagnose P. concolor the species is nonetheless distinguished from all congeners except P. deheyni and P. flexus in the possession of a prominent anterior expansion of the first pleural rib. The species is readily differentiated from both in the absence of a dominant pigmentation patterning over the flanks and caudal peduncle. Additionally, it differs from P. flexus in a shallower body depth (m. 24.9% vs. 27.0% SL), and in the possession of 7 (vs. 6) supraneurals.

DESCRIPTION: Based on the holotype and four paratypes. General appearance as in figure 6A, proportional measurements and meristic counts are given in table 5. A small-bodied species, maximum observed size 43.9 mm SL. Body elongate, laterally compressed with greatest body depth (m. 24.9% SL) well in front of dorsal-fin origin, in front of the level of pelvic-fin insertion. Dorsal body profile smoothly convex to dorsal fin, slightly less so to caudal-fin base. Ventral profile smoothly convex between isthmus and anal-fin base, caudal peduncle longer than deep. Head length short (m. 21.7% SL), eye large, bony orbit diameter m. 44.8% HL.

Mouth terminal, lower jaw prominent and slightly prognathous, lower lip thick. Premaxilla with two teeth in outer row, each bearing 3 cusps, positioned opposite interspaces between and alternating with 4 inner row teeth bearing 5–6 cusps. Four robust, broad-based, outer-row teeth on each dentary, first 3 bearing 5-6 cusps, and 4th greatly reduced in size bearing 3 cusps. Two small, conical, symphyseal teeth located immediately behind outer row series on dentary (fig. 6C). Dorsal-fin rays ii.7–8, fin positioned midway between snout and caudal-fin base, with origin at, or slightly in front of, pelvic-fin insertion, first two branched rays not elongated. Anal fin iii.15–16 rays, no hypertrophy or posterior curvature of anal fin in males. Caudal fin forked, with 9 upper and 9 lower principal rays, no median filamentous extension. Scales in longitudinal series 26–28 (mode 28) to caudal flexure, 3 or 4 transverse scales between longitudinal series and dorsal-fin origin, 3 transverse scales between longitudinal series and pelvic-fin insertion. Pored scales in truncate lateral line 5–7 (mode 6). Circumpeduncular scales 10. Vertebral count 31–33. Twelve–13 pleural ribs, first with prominent rounded expansion on anterior face in upper third (fig. 5B). Seven tubular supraneurals located between interspaces of neural spines of vertebral centra 4–11.

COLORATION: In preservation (fig. 6A), base body coloration grayish brown, darker dorsally and becoming pale yellow on chest and ventrum. An overlay of bluish iridescence covers most of body. Snout and dorsum of head dark brownish black, cheek silver with a few scattered melanophores. A large humeral blotch present at midbody, above pectoral fin. Other than humeral blotch no prominent pigmentation along flanks or caudal peduncle. Dorsal and adipose fin light gray, anal fin dusky distally, pectoral and pelvic fins hyaline with darkly pigmented leading edges. Median rays of caudal fin somewhat darker than above and below. Coloration and pigmentation shortly postmortem (fig. 1B) like that in preservation, but more intense.

DISTRIBUTION: Currently known only from the type locality, a shallow pool like expansion of the Ndzaa River (fig. 2, upper panel), about 25 km upstream of the outflow of the Ndzaa into the Mfimi (fig. 1).

ETYMOLOGY: Concolor, from the Latin, meaning of the same, or uniform, color. Named in reference to the absence of prominent pattern of black pigmentation along the flanks and caudal peduncle.

COMPARATIVE MATERIALS EXAMINED: Alestopetersius hilgendorfii: AMNH 244114, 5 specimens, 1CT, 1C&S, Democratic Republic of Congo, Salonga National Park, Yenge River at Boyenga. – MRAC 829, lectotype, Kutu. – Alestopetersius brichardi: AMNH 240416, 5 specimens, 1C&S, Republic of Congo, Cuvette Ouest, Odzala National Forest, au campement des pêcheurs. – MRAC 121105, holotype, Yangambi, Lac Yandja. – Alestopetersius nigropterus: AMNH 274754, 1 specimen, Democratic Republic of Congo, Mai-Ndombe Province, Nioki Port Market, main channel Mfimi River.

Nannopetersius ansorgii: AMNH 263093, 5 specimens, 1CT, Republic of Congo, Kouilou Province, Lake Tchibanji. – NHMUK 1910.11.28:71, lectotype, Angola, Bengo River at Cabiri and Lake Kilungu. – Nannopetersius lamberti: AMNH 253898, 5 specimens, 2C&S, Republic of Congo, Passi-passi River.

Clupeocharax schoutedeni: AMNH 274775, 1 specimen, Democratic Republic of Congo, Mai-Ndombe Province, Lomomo River near confluence with Mfimi.

Phenacogrammus aurantiacus: AMNH 274780, 3 specimens, 2CT, Democratic Republic of Congo, Mai-Ndombe Province, Ndzaa River. – AMNH 2474779, 3 specimens, Democratic Republic of Congo, Mai-Ndombe Province, Mfimi River around Nioki Port. – AMNH 260346, 5 specimens, Central African Republic, Dzanga-Sangha Protected Area. – AMNH 262366, 1 specimen, Gabon, Ogowe-Ivindo, WCTS Forestry Concession, Site 2. – AMNH 274861, 4 specimens, Republic of Congo, Kouyou River at Owando, 1 hour upstream from the bridge.

Phenacogrammus deheyni: 244045, 2 specimens, 1CT, Democratic Republic of Congo, Salonga National Park, Salonga River at Bokuma. – AMNH 244047, 1 specimen, 1CT, Democratic Republic of Congo, Salonga National Park, Yenge River at Boyenga. – AMNH 252208, 2 specimens, 1CT, Democratic Republic of Congo, Salonga National Park, Bionga Bionga. – MRAC 57789, holotype, Mumbia, Territory of Lisala. – AMNH 252277, 3 specimens, Democratic Republic of Congo, Mpongo stream ca. 2 km from Luilaka River. – AMNH 252194, 1 specimen, Democratic Republic of Congo, Ta’Simon River at Boaugi.

Phenacogrammus interruptus: AMNH 274784, 2 specimens, 2CT, Democratic Republic of Congo, Mai-Ndombe Province, Lomomo River near Kilako. – AMNH 256217, 3 specimens, 1C&S, Democratic Republic of Congo, Kwilu River at Kwilu beach. – AMNH 268936, 1 specimen, Democratic Republic of Congo, Kinshasa Province, Pool Malebo at Kinkole. – MRAC 817, lectotype, Stanley Pool. – CU 89868, 1 specimen, Republic of Congo, Lekoli River, Odzala National Park. – AMNH 247289, 1 specimen, Democratic Republic of Congo, Kongo Central Province, rockes below CO8-028 near Bulu. – AMNH 233442, 1 specimen, Aquarium purchase, no locality data.

Phenacogrammus major: AMNH 236514, 1 specimen, 1CT, Cameroon, Pont So’o at confluence of the So’o and Fala Rivers.

Phenacogrammus polli: AMNH 240816, 3 specimens, 2CT, Democratic Republic of Congo, Salonga National Park, Luilaka River at Nkombe-Dunda. – AMNH 273785, 4 specimens, Democratic Republic of Congo, Salonga National Park, Luilaka River at Ifumu. – AMNH 240793, 5 specimens, 2C&S, Democratic Republic of Congo, Salonga National Park, Luilaka River at Boangi Village. – MRAC 125500, holotype, River Lomela at Lomela.

Phenacogrammus taeniatus: ZSM 36901, Cameroon, Southeast Province, Sangha River at Libongo.

Phenacogrammus urotaenia: AMNH 253971, 5 specimens, 1CT, Republic of Congo, Kouilou Province, Lebayi River. – AMNH 262979, 5 specimens, 1C&S, Gabon, Ogowe-Ivindo, small affluent of the Gniabale River. – AMNH 262365, 1 specimen, Gabon, Ogowe-Ivindo, WCTS Forestry Concession, Site 2.