Zoosyst. Evol. 100 (1) 2024, 309-324 | DOI 10.3897/zse.100.116535 Ate BERLIN Bashimyzon cheni, a new genus and species of sucker loach (Teleoste1, Gastromyzontidae) from South China Xiong Gong?, E Zhang? 1 Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, China 2 University of Chinese Academy of Sciences, Beijing, China https://zoobank. org/634807EE-E59F-4698-853D-B757COOAEB99 Corresponding author: E Zhang (zhange@ihb.ac.cn) Academic editor: Nicolas Hubert # Received 29 November 2023 # Accepted 27 February 2024 @ Published 20 March 2024 Abstract Bashimyzon, new genus, is here established for Erromyzon damingshanensis, and a new species of the genus is described from the You-Jiang of the Pearl River (=Zhu-Jiang in mandarin Chinese) basin in Guangxi Province, South China. This new genus has a small gill opening above the pectoral-fin base and short pectoral fins extending backwards short of pelvic-fin insertions, both characters combined to separate it from all currently-recognized gastromyzontid genera except Erromyzon and Protomyzon, but differs from the two genera in having a larger gap between the posterior edge of eye and the vertical through the pectoral-fin insertion and very small fleshy lobes posterior to the maxillary-barbel bases. It is further distinct from its most similar genus Erromyzon in having a relatively larger gill opening, fewer branched pectoral-fin rays folded against body, and more posteriorly placed pectoral fins with a shorter fin base. Bashimyzon cheni, new species, and B. damingshanensis, the single congeneric species, differ in number of lateral-line pored scales, body coloration, and cephalic contour, and also in substantial genetic divergence. Key Words Bashimyzon, new genus, new species, taxonomy, Zhu-Jiang basin Introduction Species of the family Gastromyzontidae (so-called sucker loaches) are small-sized bottom dwellers, mainly feeding on algae scraped off underwater rocks (Chen 1980a; Chen and Tang 2000; Chen and Zhang 2006). These species are adapted to dwell in rapid-running waters by evolv- ing many morphological traits, such as a depressed head, an inferior mouth, and laterally-expanded pectoral and pelvic fins (Chen 1978; Chen and Zheng 1989; Kottelat 2004). This family is by far among the lesser-known taxonomic freshwater fish groups, and new species are described each year (Kottelat 2012; Zhang and Cao 2021). Numerous unidentified species are waiting for formal descriptions. There are a total of 20 valid genera currently rec- ognized in the Gastromyzontidae (Fricke et al. 2023). Kottelat (2004) proposed Erromyzon to accommodate a Chinese species formerly misplaced in the genus Protomyzon Hora, 1932 (P. sinensis), and described a new species £. compactus from northeastern Vietnam. Subsequently, three new species were described from South China: EF. yangi by Neely et al. (2007), E. kalo- taenia by Yang et al. (2012) and E. damingshanensis by Xiu and Yang (2017). In Kottelat’s (2012) inventory of the loaches (Teleostei, Cypriniformes, Cobitoide1) of the world, 17 valid genera were included in the Gastromy- zontidae. Nevertheless, its generic classification remains far from satisfactory mainly due to a poor understanding of the phylogenetic relationships within the family. Fol- lowing the erection of Erromyzon, two new genera were erected: Yaoshania by Yang et al. (2012) and Engkaria by Tan (2021). Labigastromyzon have been elevated to ge- neric status (Chen et al. 2023). Erromyzon damingshan- ensis 1S reclassified in this study into a new genus of the Gastromyzontidae in China. Copyright Gong, X. & Zhang, E. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. 310 Currently, E. damingshanensis is found in a stream tributary to the Qingshui-He draining the northeastern slope of the Damingshan Mountain (Xiu and Yang 2017). This stream empties into the Hongshui-He of the middle Xi-Jiang basin. Our recent survey of freshwater fishes, conducted in the Wuming-He (a stream flowing into the You-Jiang) with its source in the southwestern slope of the Damingshan Mountain, yielded many specimens su- perficially most similar to E. damingshanensis but not conspecific with it or all other congeneric species, there- fore representing an unrecognized species. Further mor- phological examination and comparisons demonstrated that these two species have remarkable differences in the length of the gap between the posterior edge of eye and the vertical through the pectoral-fin insertion, gill open- ing size, number of last branched pectoral-fin rays folded against the flank, and mouth-part structures with the rest of congeneric species, which are sufficient to place both in their own genus. The generic status of Bashimyzon gen. nov. 1s also justified by its substantial genetic divergence (p-distances:10—12%) with phylogenetically allied gen- era Erromyzon and Yaoshania. The present study aims to propose a new genus Bashimyzon, with E. damingshan- ensis Xiu & Yang, 2017 used as the type species, and then provide a formal description of the unidentified species, here named as Bashimyzon cheni gen. et sp. nov. Materials and methods Specimen sampling and preservation All specimens were collected in our field surveys con- ducted during 2020-2023, in accordance with the Chi- nese Laboratory Animal Welfare and Ethics animal wel- fare laws (GB/T35892-2018). Specimens were caught using electrofishing and/or trap nets. After being anaes- thetized, all caught individuals were killed by immersion in ethanol or formalin. Some of them were stored in 10% formalin preservative for morphological examination or permanent curation, and the others in 95% ethanol for DNA extraction. The specimens examined in this study are housed in the collection of Kunming Institute of Zoology (KIZ), Chinese Academy of Sciences, Kunming City, Yunnan Province, and the Institute of Hydrobiology (THB), Chinese Academy of Sciences, Wuhan City, Hu- bei Province, P. R. China. Morphological and geometric morphometric analysis Measurements, as depicted in Fig. 1, were made point-to- point with digital calipers connected to a data recording computer and recorded to the nearest 0.1mm. Pre-dorsal, pre-pectoral, pre-pelvic and pre-anal lengths were taken from the snout tip to the dorsal-, pectoral-, pelvic- and anal-fin origin or insertion, respectively. Meristic counts zse.pensoft.net Gong, X. & Zhang, E.: Bashimyzon cheni, a new genus and species were taken with a binocular Zeiss Stereo Discovery V6, following the methods utilized by Kottelat (1990); the last two branched rays of dorsal and anal fins were count- ed as one when borne by the same pterygiophore. All morphometric measurements and meristic counts were made on the left side of specimens whenever possible. Vertebral count was taken from X-ray photographs. The Weberian apparatus is considered as including four verte- brae. GraphPad Prism 8 (GraphPad Prism Inc.) was used for the basic statistical analysis on morphometric data. Abbreviations utilized here include: GL — gill opening length, G-P — distance from the lowest extremity of the gill opening to the pectoral-fin insertion, HD — head depth, PPL — pre-pectoral length, PBL — pectoral-fin base length, and SL — standard length. Geometric morphometric (GM) analyses were utilized, targeted at cephalic contour and mouthpart structures to further distinguish B. cheni and B. damingshanensis. A total of 20 specimens were examined in GM analyses for each of these two species. Individual specimen was pho- tographed for the head in ventral and lateral views using Capture 2.3 connected to the micro-imaging cameras. The software tpsUtil 1.83 (Rohlf 2015) was used to or- dinate the digitalized images in the same file under the TPS format. The tpsDig2 software (Rohlf 2015) was used to record landmarks and semi-landmarks. The different sets and descriptions of landmarks and semi-landmarks (curve points) on the digitized image were illustrated in Fig. 2. The tps curve files were converted to landmarks data in tpsUtil 1.83 (Rohlf 2015). Subsequent data analy- ses were run using MorphoJ 1.07a software (Klingenberg 2011). A generalized Procrustes analysis (GPA) was con- ducted to scale landmarks of each specimen to a common body size, rotate each specimen to a common alignment and generate a consensus shape. Principal component analysis (PCA) was performed after checking for outliers and constructing a covariate matrix to better assess and visualize shape variation across all individuals. DNA extraction, amplification and sequencing Total genomic DNA was extracted from 95% etha- nol-stored fin or muscle tissue samples using TIANamp Genomic DNA Kit (Tiangen Biotech Co., Ltd, Beijing, China) following manufactures’ instructions. The mi- tochondrial cytochrome c oxidase subunit I (COI) gene was chosen for phylogenetic analysis. Two new pairs of specific primers were designed for amplification (COL F: ATCCTACCTGTGGCAATCAC / COIR: AATAGG- GGRAATCAGTGGAC) and sequencing (COIL FI: GCATCWGTAGACCTRACYATYTT / COLI RI: GCATARTATGCYACGACGTGRG) of the COI region in Bashimyzon and its close relatives. This gene was am- plified by the polymerase chain reaction (PCR) in 25 ul reactions containing 12.5 ul Master mix Taq (Genesand Biotech Co. Ltd., Beijing, China), 1 ul of each primer, 1 ul template DNA and 9.5ul double distilled water (dd H,O). Zoosyst. Evol. 100 (1) 2024, 309-324 311 Figure 1. Measurements taken on species of Bashimyzon and its relatives. Lateral view of body (A), and lateral (B), dorsal (C) and ventral (D) view of head. 1, standard length; 2, body depth; 3, body width crossing pectoral-fin insertions; 4, pre-dorsal length; 5, pre-pectoral length; 6, pre-pelvic length; 7, pre-anal length; 8, distance from pectoral- to pelvic-fin insertion; 9, distance from pel- vic-fin insertion to anal-fin origin; 10, distance from anus to anal-fin origin; 11, pectoral-fin base length; 12, pelvic-fin base length; 13, dorsal-fin base length; 14, anal-fin base length; 15, caudal-peduncle length; 16, caudal-peduncle depth; 17, pectoral-fin length; 18, pelvic-fin length; 19, anal-fin length; 20, dorsal-fin length; 21, head length; 22, head depth; 23, head width; 24, width between upper extremities of gill openings; 25, snout length; 26, eye diameter; 27, interorbital width; 28, mouth width; 29, gill opening length; 30, distance from lowest extremity of gill opening to pectoral-fin insertion; 31, distance between posterior edge of eye and vertical through pectoral-fin insertion. The PCR conditions were given as follows: initial dena- turation at 95 °C for 3min followed by 35 cycles of 94 °C for 25s, 54 °C for 25s, and elongation at 72 °C for 45s; and final extension at 72 °C for Smin. Amplified products were stored at 4 °C. The sequencing was done through Aokedingsheng Biotechnology Company (Wuhan, Chi- na). All sequences amplified in this study were submitted to GenBank. Phylogenetic analyses The amplified 158 gene sequences from six species, namely EF. sinensis (26), E. compactus (two), E. yangi (32), E. kalotaenia (20), B. damingshanensis (43), and B. cheni (35), were utilized for molecular phylogenet- ic analysis along with other seven GenBank-retrieved sequences of the same gene from three outgroups: Sinogastromyzon tonkinensis (KY 352773), Vanmane- nia pingchowensis (KP005457) and Yaoshania pachy- chilus (AP012132, KT031050, KX588239, KY352775 and NC030634). Detailed information on specimens used for molecular analysis in this study are given in Table 1. Raw sequences were edited using Seqman in DNAstar (DNAStar Inc., Madison, WI, USA), aligned with Seaview v4.2.5 (Gouy et al. 2010), and checked by eye for some ambiguous alignments. Nucleotide sequences were initially aligned utilizing Clustal X v2.0 (Larkin et al. 2007) with default parameters, and then re-checked visually. The sequence data were translated into amino acids in MEGA v7.0 (Kumar et al. 2016) to confirm the absence of premature stop codons. Then DnaSP v6 (Rozas et al. 2017) was used for genetic diversity analyses and filter the haplotype. zse.pensoft.net a2 Gong, X. & Zhang, E.: Bashimyzon cheni, a new genus and species Figure 2. Landmarks (pink dot) and semi-landmarks (red diamond) used in geometric morphometrics. Photographs of B. cheni, THB 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 max- illary-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. Table 1. Detailed information of specimens used for molecular phylogenetic analyses in this study. Species N Specimen voucher Sampling localities Haplotypes GenBank no. E. sinensis 21 IHB 202203177109, 20, 27- Liuding-He, GuiJiang, tributary of Zhu- Hap 1-6 OR744909-29 34, 36, 42-46, 51-53, 55-56 Jiang, Changle Village, Jinxiu County, China 5 IHB 202010049920-24 Lu-Jiang, Gui-Jiang, tributary of Zhu-Jiang, Hap5, 7-9 OR744930-34 Lujiang Village, Lingchuan County, China E. compactus 2 1|HB 01-QN-2023, 02-QN-2023 Ba Che River, Ba Che city, Ba Che District, | Hapl0-11 OR744935-36 Quang Ninh Province, Vietnam E. yangi 27 IHB 202203177157-59, Meicun-He, Liu-Jiang, tributary of Zhu- Hap12-15 OR744937-63 62-85 Jiang, Meicun Village, Jinxiu County, China 5 IHB 202104053762-66 Shuijing-He, Liu-Jiang, tributary of Zhu. Hapl3,15-16 OR/44964-68 Jiang, Heping Village, Jinxiu County, China E, kalotaenia 18 IHB 202203177107-08, Liuding-He, GuiJiang, tributary of Zhu- Hap1 7-18 OR744969-86 10-19, 21-26 Jiang, Changle Village, Jinxiu County, China 2 IHB 202203177160-61 Dishui-He, GuiJiang, tributary of Zhu-Jiang, Hap17 OR744987-88 Shibajia Village, Jinxiu County, China B. damingshanensis 3 IHB 202109136061-63 Qingshui-He, Hongshui-He, tributary of Zhu- Hap19 OR744989-91 Jiang, Shanglin County, China 40 IHB 202109136064-103 Qingshui-He, Hongshui-He, tributary of Hapl9-20 OR7/744992-5031 Zhu-Jiang, Naxue Village, Dafeng Town, Shanglin County, China B. cheni 20 IHB 202109136104-23 Wuming-He, You-Jiang, tributary of Zhu- Hap21-22 OR745032-51 Jiang basin, Xinyang Village, Gulin Town, Mashan County, China 15 IHB 202303064575-89 Wuming-He, You-Jiang, tributary of Zhu- Hap22 OR745052-66 Jiang basin, Jiaobei Village, Liangjiang Town, Wuming District,China The haplotype sequence matrix was used for subse- quent phylogenetic analyses. MrBayes 3.2.2 (Ronquist et al. 2012) was utilized for Bayesian inference (BI) analysis. PartitionFinder v2.1.1 (Lanfear et al. 2017) was used to select the best partitioning strategy and the optimal nucleotide substitution model for the dataset using the Bayesian information criterion (BIC). Three codon partitions and their corresponding substitution model for COI gene sequences were proposed: 1* co- don with SYM+I, 2™ with F81+I, and 3 with GTR+G. zse.pensoft.net Two independent runs were carried out with four Mon- te Carlo Markov chains (three hot chains and one cold chain) for 20 million generations to calculate posterior probability. Trees were sampled for every 1000 gener- ations. The initial 25% of sampled trees were discard- ed as burn-in. Convergence of the runs was assessed by the average standard deviation of split frequencies (< 0.01). Partitioned maximum likelihood (ML) anal- yses were conducted in RAxMLHPC v7.0 (Stamat- akis 2006) with the same partitioning strategy as for Zoosyst. Evol. 100 (1) 2024, 309-324 Bayesian inference. The more complex model (GTR + I + G) was used for all subsets, and 100 replicates ML inferences were performed with a complete random starting tree. Nodal support for the clades was estimat- ed with 1000 bootstrap pseudoreplicates (Stamatakis et al. 2008). Phylogenetic tree was edited in FigTree v1.4.2 (Rambaut 2009). Additionally, the uncorrected genetic distances (p-distances) between lineages were calculated with MEGA v7.0 (Kumar et al. 2016). Results Bashimyzon gen. nov. https://zoobank. org/1 AA6CE02-CC93-45 12-9EEC-F9298FF6A3C1 Figs 3D, 5—7 Type species. Erromyzon damingshanensis Xiu & Yang, 2017: 893 (type locality: Qingshui-He, tributary to Hong- shui-He of Zhu-Jiang basin, in Shanglin County, Guangxi Province) Diagnosis. Bashimyzon is distinct from all currently identified gastromyzontid genera except Erromyzon and Protomyzon in the presence of a gill opening restricted above pectoral-fin base (vs. gill opening elongate, extend- ing downwards to or beyond the pectoral-fin insertion to the ventral surface of head), and pectoral fins backwards extending away from (vs. close to or beyond) pelvic-fin insertions. This new genus is separated from the two gen- era in having a larger (vs. small) gap between the poste- rior edge of eye and the vertical through the pectoral-fin insertion, with the gap length being nearly equal to (vs. less than) eye diameter (Fig. 3; Table 2) and a very small fleshy lobe (vs. a relatively large fleshy lobe or enlarged papillae; see Kottelat 2004: Page 306, figs 4-6, and Yang et al. 2012: Page 176, fig. 3; Table 2) posterior to the max- illary-barbel base. Other characters useful for distinguishing Bashimyzon and Protomyzon include: upper and lower lips continuous around the corners of mouth (vs. discontinuous or inter- rupted by an arched blade-like structure; see Kottelat 2004: Page 306, figs 4-6), lower lip smooth (vs. papillated), and no externally distinct opercle (vs. present) (Table 2). J13 Bashimyzon is morphologically most similar to Erro- myzon, but further differs from it in having a relatively larger (vs. smaller) gill opening (length 46.5-60.7% of HD vs. 25.8-44.9, and the distance from its lower ex- tremity to the pectoral-fin insertion 3.6—16.1% of HD vs. 27.2-43.5; see Figs 3, 4A, B); fewer last branched pectoral-fin rays folded against the flank (3-4 vs. 7-8); and more posteriorly located pectoral fins (pre-pectoral length 17.0-22.3% of SL vs. 12.5—15.8; see Fig. 4C), with a shorter (vs. longer) base (length 8.8—10.8% of SL vs. 13.9-17.4; see Fig. 4D). Etymology. The generic name is derived from Bashi (4), the local name of the Damingshan Mountain in Zhuang nationality language, and myzon, a common suffix used in the Balitoridae. Gender masculine. The Chinese common generic name is here suggested as “7: fk JR”. Bashimyzon cheni sp. nov. https://zoobank. org/8E5656C2-1F1A-4085-962F-45D1594B1D58 Figs 5—7 Type material. Holotype. [HB 202109064273, 28.3 mm SL; Guangxi Province: Nanning City: Mashan County: Wuming-He, a stream tributary to You-Jiang of Zhu-Ji- ang 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. HB 202109064274—78, 5 specimens, 28.3-39.9 mm SL; other data same as holotype. THB 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-Ji- ang basin, at Jiaobei Village (23°31'27"N, 108°18'24"E, about 176 m above sea level) of Liangjiang Town; collect- ed 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 in- terspaces, 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 Table 2. Comparison of diagnostic characters among Bashimyzon gen. nov. and other related genera. Protomyzon auct. Gap between posterior edge of eye and small vertical through pectoralfin insertion Erromyzon s.str. small Bashimyzon gen. nov. large Arched blade-like structure between upper and lower lip Lower lip interrupted present; upper and lower lip absent; upper and lower lip absent; upper and lower lip Lowerlip = = ~—~—~—_ papillated (except for = s— 0.5), and maximum likelihood bootstrap values (> 50%) are shown, respectively. Dash represents a node with bootstrap support lower than 50%. The genetic distances (p-distances) within and be- tween genera were provided in Table 4. Intraspecific ge- netic 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 1s a monotypic genus). The intergeneric genetic distances here calculated were 10—12% (Bashimyzon / Erromyzon), 10% (Bashimyzon / Yaoshania), and 11-12% (Yaoshania / Erromyzon), respectively. Discussion It has been widely recognized that gill-opening size and pectoral-fin extension are of taxonomic importance at the generic level for the Gastromyzontidae (Pellegrin and Fang 1935; Chen 1980b; Kottelat 2004). On the basis of the two characters, the family is subdivided into four groups. The first group is composed of Annamia Hora, 1932, Formosania Oshima, 1919, Glaniopsis Bouleng- er, 1899, Katibasia Kottelat, 2004, Liniparhomaloptera Fang, 1935, Parhomaloptera Vaillant, 1902, Plesiomy- zon Zheng & Chen, 1980 and Vanmanenia Hora, 1932. These eight genera possess a large gill opening extending downwards beyond the pectoral-fin insertion to the ven- tral surface of head. The second group, comprising Para- protomyzon s. str. and Yaoshania, have an intermediate gill opening extending downwards to but not beyond the zse.pensoft.net Table 4. Genetic distances (uncorrected p-distance) of COI gene computed by MEGA v7.0 amongst 7 species of Erromy- zon, Bashimyzon and Yaoshania. Species Within 1 2 3 4 5 6 Group 1. E. sinensis 0.0021 2. E. compactus 0.0026 0.07 3. E. yangi 0.0008 0.07 0.06 4. E. kalotaenia 0.0003 0.07 0.08 0.07 5. B. damingshanensis 0.0000 0.11 0.12 O.11 0.11 6. B. cheni 0.0001 0.10 0.12 0.10 0.10 0.03 7. ¥. pachychilus 0.00192 .O:11- 0.12.02" 0.11 0.102 0,10 pectoral-fin insertion to the ventral surface of head. The third group consists of Beaufortia Hora, 1932, Engkaria Tan, 2021, Gastromyzon Gunther, 1874, Hypergastromy- zon Roberts, 1989, Labigastromyzon Tang & Chen, 1996, Neogastromyzon Popta, 1905, Pseudogastromyzon Nich- ols, 1925, and Sewellia Hora, 1932, all of them having a gill opening restricted only to a very small slit above the pectoral-fin base, and pectoral fins extending backwards beyond or close to pelvic-fin insertions. The fourth group has a relatively small gill opening above the pectoral-fin base and pectoral fins extending backwards away from pelvic-fin insertions, two characters shared with other two genera (Erromyzon and Protomyzon auct.) and also with Bashimyzon herein described. Only two species are referred to Bashimyzon: B. daming- shanensis (Xiu & Yang, 2017) and B. cheni here described. The former was previously placed in Erromyzon, a genus Zoosyst. Evol. 100 (1) 2024, 309-324 erected to include a Chinese species formerly misidenti- fied in Protomyzon and a new species of northeastern Viet- nam (Kottelat 2004). Also misplaced in Protomyzon was the type species of Yaoshania in Chinese literature. From Kottelat’s (2004) point of view, the species was unlikely to be the member of either Protomyzon or Erromyzon. It was later utilized as the type species to erect Yaoshania (Yang et al. 2012). Its generic status was confirmed in Shi et al.’s (2018) molecular phylogenetic analysis based on complete mitochondrial genomes for the superfamily Co- bitoidea. Our study demonstrated that ¥ pachychilus had a minimum genetic distance of 11% with E. kalotaenia and E. sinensis for the COI gene. And the maximum ge- netic distances of two species of Bashimyzon were 12% with E. compactus. The congeneric recognition of these species would make the maximum interspecific genetic distance (12%) of Erromyzon s.|. slightly greater than the minimum one between Yaoshania and Erromyzon (11%) (Table 4). Apparently, the generic status of Bashimyzon is justified, particularly given its monophyletic nature (see Fig. 11) and the current recognition of Erromyzon and Yaoshania, two closely allied monophyletic groups, as two distinct genera (Shi et al. 2018). The erection of Bashimyzon as a new genus highlights the need to scrutinize the classification of currently iden- tified species of Paraprotomyzon s.|., which was initially erected by Pellegrin and Fang (1935) to accommodate a new species P. multifasciatus. The original description of this species stated that it possesses a large gill opening extending downwards close to, but not beyond, the pec- toral-fin insertion. However, all other currently identified species of Paraprotomyzon, namely P. bamaensis Tang, 1997, P. lungkowensis Xie, Yang & Gong, 1984, P. ni- ulanjiangensis Lu, Lu & Mao, 2005, and P. yunnanensis Li, Mao, Lu, Sun & Lu, 1998, have a gill opening only restricted to a small slit above the pectoral-fin base (see Xie et al. 1984; Lu et al. 2005). Moreover, marked dif- ferences in mouth-part structures are also found between P. multifasciatus and these congeneric species (Tang and Chen 2000). It is more likely that these four species rep- resent their own genus, and Paraprotomyzon 1s actually a monotypic genus. The constituent species of Protomyzon also needs strict scrutiny. The type species of this genus (P. whiteheadi Vaillant, 1893) shares with P. griswoldi (Hora & Jayaram, 1952) the presence of a relatively large gill opening extend- ing downwards close to but not beyond the pectoral-fin in- sertion (see Vaillant 1893; Hora and Jayaram 1950, 1952). However, a gill opening restricted to a small slit above the pectoral-fin base is exhibited by the other two congeners: P. aphelocheilus Inger & Chin, 1962 and P. borneensis Hora & Jayaram, 1952. Given the generic-level taxonom- ic importance of gill-opening size revealed by Yang et al. (2012) and also in this study, P. whiteheadi and P. griswol- di likely belong to a distinct genus, and the taxonomy of Protomyzon needs further study in the future. The genetic distance between B. damingshanensis and B. cheni (3%) is greater than 2%, a threshold used 321 for vertebrates’ species delimitation (Avise and Walker 1999; Hebert et al. 2003), thus supporting the recognition of B. cheni as a valid species. The discovery of this new species has also conservation implications. As pointed by Tan (2006), the torrent loaches of Borneo usually have a restricted distribution; a single species is often restrict- ed only to a single stream. Their restricted distribution makes these rheophilic fishes susceptible to anthropogen- ic interferences. This is the case for B. cheni. In terms of our observation in the fieldworks, the new species has a large number of individuals currently confined only to a stream tributary to the Wuming-He in Guangxi Province of southern China. The stream drains through two scenic spots—Damingshan Mountain and Jinlun Cave. The rapid development of local tourism industry is predicted to have adverse impacts on species diversity of freshwater fishes and aquatic ecosystem. Due to the construction of many weirs across the Wuming-He for agricultural irrigation, habitats of this new species are fragmented. Its survival is thus put under threat from touristic industry and agricul- ture. In addition, the new species exhibited an extremely low genetic diversity. Only two haplotypes were detected from a total of 35 COI gene sequences of 1167 bp in length; the haplotype diversity (Hd) was 0.0571 and nucleotide diversity (Pi) was 0.00010 within the Wuming-He popula- tion (unpublished data). The presence of this new species, with fragmented populations and low genetic diversity, in a single stream can reduce its evolutionary potential and increase the risk of extinction in the wild. Therefore, con- servation efforts should be taken to preserve B. cheni. So far, B. cheni occurs in a stream with its source in the southwestern slope of the Damingshan Mountain, and so does B. damingshanensis in its northeastern slope. The allopatric distribution of this sister pair suggests that the uplift of the Damingshan Mountain has been acting as the driving force of speciation between both. In such a small scale, mountain build-up plays a crucial role in speciation of these two species. Given that the species of Erromyzon also have a montane distribution, it 1s speculated that the Species diversity of the genus in China is underestimated. More in-depth taxonomic research is urgently required for widespread species such as EF. sinensis. Comparative material Erromyzon sinensis: VHB 75-1V-2572—2574, 75-IV- 2579, 75-IV-2581, 5 specimens, syntypes, 33.9-53.3 mm SL, Xiuren Town, Lipu County, Guilin City, Guangxi Province, China; [HB 75-V-2804, 1 specimen, syn- type, 30.3 mm SL, Lipu County, Guilin City, Guangxi Province, China; IHB 202203064279-88, 10 specimens, 32.63—38.40 mm SL, Liuding-He, Gui-Jiang, tributary of Zhu-Jiang, Changle Village, Jinxiu County, Laibin City, Guangxi Province, China; [HB 202010051119—23, 5 specimens, 39.74-47.85 mm SL, Lu-Jiang, Gui-Ji- ang, tributary of Zhu-Jiang, Lujiang Village, Lingchuan County, Guilin City, Guangxi Province, China. zse.pensoft.net 322 Erromyzon compactus. ZRC 49636, holotype, 30.8 mm SL, Ba Che River, a river that flows independently into the sea, Ba Che City, Ba Che District, Quang Ninh Prov- ince, Vietnam (photograph examined); [HB 01-QN-2023, 02-QN-2023, 2 specimens, 48.95-59.52 mm SL, other data same as the holotype. Erromyzon yangi. KIZ 200304423, holotype, 42.8 mm SL, Meicun-He, Liu-Jiang, tributary of Zhu-Jiang, Meicun Village, Jinxiu County, Laib- in City, Guangxi Province, China; KIZ 200304422, 2003004424, 2 specimens, paratypes, 36.7—37.1 mm SL, other data same as holotype; IHB 2017056658-61, 2017056678—83, 10 specimens, 26.83-47.47 mm SL, other data same as holotype; IHB 202104052295-99, 202203064413-—18, 11 specimens, 41.02—52.45 mm SL, Shuiying-He, Liu-Jiang, tributary of Zhu-Jiang, Heping Village, Jinxiu Town, Jinxiu County, Laibin City, Guangx! Province, China. Erromyzon kalotaenia: KIZ 200304310, holotype, 41.3 mm SL, Liuding-He, Gui-Jiang, tributary of Zhu-Ji- ang, Changle Village, Jinxiu County, Laibin City, Guangxi Province, China; KIZ 200304313-14, 200304317, 3 specimens, paratypes, 46.9-47.9 mm SL, other data same as holotype; KIZ 200304049-52, 200304071, 5 specimens, paratypes, 32.4-45.8 mm SL, Dishui-He, Gui-Jiang, tributary of Zhu-Jiang, Shibajia Village, Jinx- iu County, Laibin City, Guangxi Province, China; [HB 202203064289-4303, 15 specimens, 27.78—-40.13 mm SL, other data same as holotype. Bashimyzon damingshanensis: K1Z 2014091301, holo- type, 48.2 mm SL, Qingshui-He, Hongshui-He, tributary of Zhu-Jiang, Naxue Village, Dafeng Town, Shanglin County, Nanning City, Guangxi Province, China; KIZ2014091302, 2014091304—08, 5 specimens, paratypes, 43.8-47.3 mm SL, same data as the holotype (photograph examined); [HB 202109064253—4272, 20 specimens, 30.57-49.65 mm SL, other data same as the holotype. Ethics approval and consent to participate All procedures described in this paper were in accordance with Chinese laws and were licensed by the Ministry of Ecol- ogy and Environment of the People’s Republic of China. Availability of data and material The datasets used and/or analyzed during the current study are available from the corresponding author on rea- sonable request. Competing interests The authors declare that they have no competing interests. zse.pensoft.net Gong, X. & Zhang, E.: Bashimyzon cheni, a new genus and species Funding This work was supported by the special foundation for Natural Science and Technology Basic Research Program of China (2019FY101900) and a grant from the Nation- al Natural Science Foundation of China (NSFC No. 31872200). Authors’ contributions Xiong Gong conceived the study and conducted the data analysis. Xiong Gong led the writing and E Zhang re- vised the manuscript. All authors contributed to the writ- ing of the paper. 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