Hylopanchax paucisquamatus, Sonnenberg, Rainer, Friel, John P. & Van Der Zee, Jouke R., 2014

Sonnenberg, Rainer, Friel, John P. & Van Der Zee, Jouke R., 2014, Description of Hylopanchax paucisquamatus (Cyprinodontiformes: Poeciliidae), a new lampeye species from the Odzala-Kokoua National Park, Republic of Congo, Zootaxa 3846 (4), pp. 577-583 : 580-581

Hylopanchax paucisquamatus , new species

( Figs. 2–4 , Table 1 )

Hylopanchax sp. Odzala in: Van der Zee, Sonnenberg & Schliewen, 2013.

Holotype. CUMV 97967, male, 24.0 mm SL, Republic of Congo, Cuvette-Ouest Province, Mbomo District, small forest stream along trail to Lokoué saline, Odzala-Kokoua National Park, Likouala River drainage (0.9169444° N, 15.1561108° E), coll. J. P. Friel, S. Lavoué & J. P. Sullivan, 29 August 2002.

Paratypes. CUMV 87662, 1 male, 26.1 mm SL, 2 females, 22.0– 22.6 mm SL (the right eye of the larger female is lost), same collection data as the holotype.

Diagnosis. Hylopanchax paucisquamatus shows the diagnostic characters of the genus, which are: anterior flank scales larger than scales on caudal peduncle, crescent-shaped dark markings on anterior side of scales, black male urogenital papilla, large round urogenital papilla in females, narrow dark band along base of anal-fin (faint in the studied specimens), low number of scales in the mid-longitudinal series compared to related poeciliid genera, branchiostegal appendages in adult males, and supra-orbital neuromast grooves straight and parallel (Van der Zee et al. 2013; Van der Zee et al. submitted).

It is distinguished from all other known Hylopanchax species by a unique combination of morphological characters. By body shape, it belongs to the group of more deep-bodied species in the genus ( H. leki , H. ndeko , H. sp. Bena Tshadi). From the small, very slender H. moke it is distinguished by a deeper body (26.1–27.2 % SL vs. 16.3–20.2 % SL), larger size (22.0– 26.1 mm SL vs. max 21.2 mm SL), a longer head (26.7–29.6 % SL vs. 17.9–23.7 % SL), a deeper caudal peduncle (11.8–12.2 % SL vs. 7.7–11.3 % SL), a longer dorsal-fin base (11.7–13.1 % SL vs. 5.9–9.9 % SL), a lower number of mid-longitudinal scales (19–21 vs. 23–26), a higher number of dorsal-fin rays (9–11 vs. 6 or 7) and insertion of dorsal-fin above anal-fin ray 8 or 9 (vs. 11–14).

From the slender H. stictopleuron and H. silvestris it is distinguished by a deeper body (26.1–27.2 % SL vs. 20.8–21.0 % SL [ H. stictopleuron ] or 22.2–26.3 % SL [ H. silvestris ]), a slightly higher number of dorsal-fin rays (8 or 9 vs. 6–8), a more anterior origin of dorsal-fin in relation to anal-fin (D/A 8 or 9 vs. 12 or 13), and a lower number of mid-longitudinal scales (19–21 vs. 24 or 25).

Hylopanchax paucisquamatus is distinguished from the two described deep-bodied species H. leki and H. ndeko by a longer predorsal distance (68.8–70.7 % SL vs. 61.0–67.8 % SL), a narrower caudal peduncle and higher caudal peduncle ratio (11.8–12.2 % SL and 1.8–1.9 vs. 12.2–15.5 % SL and 1.2–1.7), a shorter dorsal-fin base (11.7–13.1 % SL vs. 15.6–22.2 % SL), a lower number of transverse scales (15 or 16 vs. 18–22), a slightly lower number of dorsal-fin rays (9–11 vs. 11–14), a lower to slightly lower number of mid-longitudinal scales (19–21 vs. 24–26 [ H. ndeko ] or 21–23 [ H. leki ]). It can also be distinguished from H. leki by a less deep body (26.1–27.2 % SL vs. 29.2–35.5 % SL) and from H. ndeko by a longer caudal peduncle (21.8–23.0 % SL vs. 16.5–20.8 % SL).

Description. See Figures 2 and 3 for general appearance and Table 1 for morphometric and meristic data of the types. A relatively deep-bodied Hylopanchax species, laterally strongly compressed; dorsal profile convex, greatest body depth approximately at pelvic-fin base; ventral profile convex from snout to end of anal-fin, concave on ventral caudal peduncle; snout rounded, mouth directed upwards, lower jaw longer than upper jaw; outer row of larger and slightly curved conical teeth on both jaws, inner row with smaller and more irregularly arranged teeth, symphysis forming ridge on lower and upper jaw, branchiostegal appendages present in adult males. Frontal or nasal neuromast system absent, one pre-orbital neuromast in short, shallow open groove; post-orbital and supra-orbital neuromast system provided with large neuromasts and large lobes, covering a great part of the groove; pre-opercular neuromast system with 5 pores.

Total number vertebrae 29 or 30; hypurals fused into one large plate, 8 or 9 caudal-fin rays attached to hypural plate, posterior neural and hemal spines flattened. Scales cycloid, body completely scaled except ventral head surface, 1 or 2 rows of scales underneath eye, frontal head squamation of G-type, no scales on dorsal- and anal-fin base, scales on mid-longitudinal series (LS) 19–21, 3 or 4 scales posterior to hypural plate on caudal-fin base. Number of dorsal-fin rays 9 or 10, anal-fin rays 17 or 18, caudal-fin rays 25 or 26, pectoral-fin rays 12 or 13. First dorsal-fin ray above anal-fin ray 8 or 9.

Colouration. Preserved specimens brownish, darker on head, lighter ventrally. Body covered with small melanophores, denser on dorsal and lateral scales, less dense on ventral. Fins translucent, paired fins brownish, dorsal with dark spots. Faint narrow dark band present at base of anal-fin, crescent-shaped markings on flank scales, darker and broader on anterior large scales, urogenital papilla dark in males and ringed with dark pigmentation in females. Colouration of this species in life currently not known.

Distribution. Hylopanchax paucisquamatus is at the present time only known from its type locality in Odzala- Kokoua National Park in the Republic of Congo, the westernmost known locality of deep-bodied species of the genus and also the only locality north of the Congo River. The remaining three species ( H. leki , H. ndeko , and H. sp. Bena Tshadi) are currently only known from the southern and central Congo basin in tributaries of the Kasaï River basin.

Other fish species collected at the type locality included: Marcusenius moorii , Mormyrops zanclirostris , Paramormyrops kingsleyae, Stomatorhinus sp., Barbus sp., Clarias sp., Epiplatys chevalieri , and Microctenopoma nanum .

Etymology. The name is in reference to the low number of lateral line scales, from paucus = few and squamatus = scaled.

Figures

FIGURE 2. Hylopanchax paucisquamatus, new species, holotype, male, CUMV 97967, 24.0 mm SL. Scale bar represents 10 mm.

FIGURE 3. Hylopanchax paucisquamatus, new species, paratype, female, CUMV 87662, 22.0 mm SL. Scale bar represents 10 mm.

FIGURE 4. Hylopanchax paucisquamatus, new species, holotype, male, CUMV 97967, 24.0 mm SL, X-ray.