Bashimyzon cheni, Gong & Zhang, 2024

Gong, Xiong & Zhang, E, 2024, Bashimyzon cheni, a new genus and species of sucker loach (Teleostei, Gastromyzontidae) from South China, Zoosystematics and Evolution 100 (1), pp. 309-324 : 309

Bashimyzon cheni sp. nov.

Figs 5 , 6 , 7

Type material.

Holotype. IHB 202109064273, 28.3 mm SL; Guangxi Province: Nanning City: Mashan County: Wuming-He, a stream tributary to You-Jiang of Zhu-Jiang basin, at Xinyang Village (23°35'05"N, 108°15'38"E, roughly 237m above sea level) of Gulin Town; collected by X. Gong, D. M. Guo and Y. Liu; 17 September 2021.

Paratypes. IHB 202109064274-78, 5 specimens, 28.3-39.9 mm SL; other data same as holotype. IHB 202303064712-36, 25 specimens, 35.0-42.7 mm SL; Guangxi Province: Nanning City: Wuming District: Wuming-He, a stream tributary to You-Jiang of Zhu-Jiang basin, at Jiaobei Village (23°31'27"N, 108°18'24"E, about 176 m above sea level) of Liangjiang Town; collected by X. Gong, D. M. Guo and P. Shan; 21 March 2023.

Diagnosis.

Bashimyzon cheni is clearly distinguished from the single congeneric species B. damingshanensis in having 8-9 teardrop-shaped black blotches wider than interspaces, with the majority portion of each blotch located above the lateral line on the flank (vs. 12 irregular black bars narrower than interspaces, and located along the lateral line on the flank; see Figs 5 , 6 ); fewer rows of blackish spots across dorsal-fin rays (3 vs. 4); fewer lateral-line pored scales (84-86 vs. 88-95); a gradual (vs. abrupt) upward dorsal profile of head in front of nostrils (Fig. 8A ); a deeply (vs. slightly) curved rostral groove, or the greater (vs. less) distance from the median point of the distal margin of the upper lip to the anterior-most tip of the snout than half of the mouth width (Fig. 8B ), a distinct (vs. indistinct) incision on both side of the fleshy pad of the lower lip (Figs 2B , 7 ).

Description.

General body shape and appearance illustrated in Figs 5 , 6 and lateral view of head in Fig. 7 . Morphometric measurements and meristic counts provided in Table 3 . Body moderately elongate, anteriorly nearly cylindrical, slightly deeper than wide or both equal, and posteriorly compressed laterally, with greatest depth at dorsal-fin origin, and greatest width at middle of pectoral-fin base. Caudal peduncle stout, deeper than long, with minimum caudal-peduncle depth closer to caudal-fin base. Dorsal profile of head gradually rising from anterior-most tip of snout to posterior end of supraoccipital and predorsal body slightly convex or straight; dorsal profile of dorsal-fin base and post-dorsal body slightly concave. Ventral profile of head straight, then slightly convex from pectoral-fin insertion to anal-fin origin, and evenly rising towards caudal-fin base.

Head longer than deep, and shallower than wide. Snout broadly rounded in dorsal view and obtuse in lateral view, nearly equal to postorbital head. Eyes small, situated dorsolaterally in half of head, with broad and slightly flat interorbital space. Anterior and posterior nostrils close together, and short tubular flap on anterior nostril. Mouth small, inferior and arched in ventral view. Rostral fold modified into three rounded, fleshy lobes; median one wider than or equal to two lateral ones, separated from upper lip by distinct shallow groove. Lips fleshy and smooth; upper lip broad and curved, reflected on base of upper jaw; lower lip restricted to corners of mouth. Upper and lower lips continuous around corner of mouth, with small notch on confluence between both anterior to corners of mouth. A small papilla present on this notch, but indistinct in some individuals. Postlabial groove widely interrupted, or short and restricted only to corners of mouth, so leaving an anteriorly bilobed median fleshy pad on chin. A distinct incision also on both side of the fleshy pad. Upper and lower jaws bearing thick, flexible horny sheaths on cutting edges. Lower jaw largely exposed. Two pairs of rostral barbels; outer pair larger than inner pair. Maxillary-barbel pair rooted at corners of mouth, longer than rostral-barbel pair. A very small fleshy lobe posterior to maxillary barbel present on lower lip. Gill opening relatively large above pectoral-fin base, with its lower extremity extending away from the pectoral-fin insertion.

Scales minute, cycloid. Lateral line complete, with 84-86 pored scales, slightly curved upwards about half of pectoral-fin length, then downwards to posterior end of anal-fin base, extending along middle of caudal-peduncle to caudal-fin base. No scales on head, abdomen adjacent to ventral midline extending for three-fourths of distance between pectoral- to pelvic-fin insertions, and post-pelvic ventral region in front of anus. Numerous small tubercles densely distributed in suborbital portions of head and sides of snout; not obvious in other areas of body. Vertebrae 4+29-30.

Dorsal fin with three unbranched and seven branched rays; distal margin truncate or straight; origin anterior to pelvic-fin insertion, and closer to caudal-fin base than to snout tip. Pectoral fins with three unbranched and seven branched rays, enlarged and expanded laterally, longer than head; inserted slightly in front of lowest extremity of gill opening; tip of adpressed fin extending away from pelvic-fin insertion; last three or four branched rays folded dorsally against flank, shorter than others. Gap between posterior margin of eye and vertical through pectoral-fin insertion nearly equal to eye diameter. Pelvic fins short and not fused, with one unbranched and seven or eight branched rays; inserted slightly closer to caudal-fin base than to snout tip; tip of adpressed fin reaching anus, but far away from anal-fin origin. Anal fin with two unbranched and five branched rays; distal margin truncate; origin closer to caudal-fin base than to pelvic-fin insertion; and tip of adpressed fin reaching caudal-fin base. Anus located midway from posterior end of pelvic-fin base to anal-fin origin or slightly behind. Caudal-fin emarginated, lower lobe slightly longer than upper lobe.

Coloration.

In freshly-captured specimens, background of body yellowish or whitish yellow, with 8-9 vertical brown blotches of variable size on flank, oblong prodorsally and teardrop-shaped below dorsal-fin base and postdorsally (Fig. 6B ). In formalin-stored individuals, body faded to lighter brown. Blotches on flank only 2/3 of body depth, wider than interspaces, and interrupted on dorsum. Dorsal surface of body covered with 7-8 dark elliptical patches along dorsal midline; predorsal patches usually linked to each other. Body pale yellowish-cream on ventral and ventrolateral surfaces, with some small blackish blotches located above pelvic-fin base. Pectoral-fin base lightly speckled with three to four irregular dark brown spots; pelvic fins and anal fin hyaline. Three rows of blackish spots on dorsal-fin rays, and two or three rows on caudal-fin rays; a relatively large black bar at caudal-fin base. Sides of head yellowish brown to black, with dark brown vermiculations visible.

Distribution and habitat.

Bashimyzon cheni is so far known from the Wuming-He, a stream tributary to the You-Jiang discharging into the Xi-Jiang of the Zhu-Jiang basin, in Guangxi Province, China (Fig. 9 ). It was caught in shallow fast-flowing waters, at depths of 0.2-0.8 m, with a mixed bottom substrate of boulders, cobbles, and sands (Fig. 10 ). Coexisting species included Opsariichthys bidens , Osteochilus salsburyi , Schistura fasciolata , Traccatichthys pulcher , Mystus guttatus , Glyptothorax fokiensis , and Mastacembelus armatus .

Etymology.

The specific epithet is named after Prof. Chen Yi-Yu, a Chinese Academician, in honor for his great contribution to Chinese freshwater fish research. In particular, he discovered and named the type species of Erromyzon and Yaoshania , which are two close relatives of the genus under description. The Chinese common specific name “陈氏岜是鳅” is here suggested.

Sequence variation and molecular phylogeny

A total of 158 COI gene sequences of 1167 bp (base pair) in length from all four species of Erromyzon , and two species of Bashimyzon were amplified in this study (Table 1 ). These sequences were used for molecular phylogenetic analysis together with three outgroups: Sinogastromyzon tonkinensis (one), Vanmanenia pingchowensis (one), and Yaoshania pachychilus (five). Twenty-seven haplotypes (22 and five, respectively for ingroups and outgroups) were detected from the sequences (Table 1 ). The haplotype sequences matrix consisted of 833 conserved sites, 334 variable sites, 259 parsimony informative sites and 75 singleton sites. The nucleotide frequencies were 25.2% (A), 29.4% (T), 25.8% (C), and 19.5% (G).

Given that BI and ML analyses produced overall identical topologies, only the BI tree with Bayesian posterior probabilities (PP) and bootstrap support (BS) value were presented in Fig. 11 . From the tree topologies, samples of B. cheni were strongly supported (PP = 1.0 / BS = 100) to group into a lineage further forming a well-supported (PP = 1.0 / BS = 100) clade together with those of B. damingshanensis . Bashimyzon was weakly supported (PP = 0.57 / BS = 51) to stand as the sister group consisting of sampled species of Erromyzon ( E. sinensis , E. compactus , E. yangi and E. kalotaenia ). The two genera together were highly supported (PP = 1.0 / BS = 94) to be sister of Yaoshania .

The genetic distances (p-distances) within and between genera were provided in Table 4 . Intraspecific genetic distances were 0.03-0.26%, 0.0-0.01%, and 0.19% for sampled species of Erromyzon , Bashimyzon and Yaoshania , respectively. Interspecific genetic distances were 6-8% for Erromyzon , 3% for Bashimyzon and NA for Yaoshania (not available owing to the fact that it is a monotypic genus). The intergeneric genetic distances here calculated were 10-12% ( Bashimyzon / Erromyzon ), 10% ( Bashimyzon / Yaoshania ), and 11-12% ( Yaoshania / Erromyzon ), respectively.

Figures

Figure 2. Landmarks (pink dot) and semi-landmarks (red diamond) used in geometric morphometrics. Photographs of B. cheni, IHB 202303064716, 42.7 mm SL. A. Lateral view of head; 1 - 5 landmark points (anterior-most tip of snout, topmost, hindmost and lowermost point of gill opening, and pectoral-fin insertion), and 6 - 20 semi-landmark points to which the curve from the maxillary-barbel root to the posteromedial tip of the supraoccipital was resampled by length; B. Ventral view of head; 1 - 6 landmark points (roots of left and right maxillary barbels, left and right lateral end of upper lip, anterior-most tip of snout, and median point of distal margin of upper lip), and 7 - 19 semi-landmark points to which the curve between the left and right end of the rostral groove was resampled by length.

Figure 5. Dorsal (top), lateral (middle) and ventral (bottom) views of body in B. cheni, IHB 202109064273, holotype, 28.3 mm SL; China: Guangxi Province: Nanning City: Mashan County: Wuming-He, a stream tributary to You-Jiang of Zhu-Jiang basin, at Xinyang Village of Gulin Town.

Figure 6. Lateral view of freshly captured individual of A. B. damingshanensis, IHB 202109064259, topotype, 30.8 mm SL; China: Guangxi Province: Shanglin County: Qingshui-He at Naxue Village of Dafeng Town; and B. B. cheni, IHB 202109064273, holotype, 28.3 mm SL; China: Guangxi Province: Mashan County: Wuming-He at Xinyang Village of Gulin Town.

Figure 7. Ventral view of mouth in A. B. damingshanensis, IHB 202109064259, topotype, 30.8 mm SL; B. B. cheni, IHB 202109064273, holotype, 28.3 mm SL. fl - flesh lobe; lj - lower jaw; ll - lower lip; mb - maxillary barbel; rg - rostral groove; rf - rostral fold; rb - rostral barbels; sp - small papilla; uj - upper jaw; ul - upper lip.

Figure 8. Scatterplots for the first two principal components (PC 1 and PC 2) of B. cheni (red dot) and B. damingshanensis (blue dot) principal component analyses for contours of the lateral head (A) and mouth-part structures (B).

Figure 9. Map showing the two sampling sites of the type specimens of B. cheni. S 1, Xinyang Village, Gulin Town, Mashan County, and S 2, Jiaobei Village, Liangjiang Town, Wuming District, Nanning City, Guangxi Province, P. R. China.

Figure 10. Sampling locality of the holotype (IHB 202109064273) of B. cheni in the Wuming-He, tributary to the You-Jiang in Xinyang Village, Gulin Town, Mashan County, Nanning City, Guangxi Province, P. R. China; 17 September 2021, photographed by Yi Liu.

Figure 11. Bayesian Inference tree derived from the mitochondrial COI gene for seven analyzed species of three genera (Erromyzon, Bashimyzon, and Yaoshania). Bayesian posterior probabilities (> 0.5), and maximum likelihood bootstrap values (> 50 %) are shown, respectively. Dash represents a node with bootstrap support lower than 50 %.