Bashimyzon cheni , a new genus and species of sucker loach (Teleostei, Gastromyzontidae) from South China

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.


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 evolving 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 recognized 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 E. compactus from northeastern Vietnam.Subsequently, three new species were described from South China: E. yangi by Neely et al. (2007), E. kalotaenia by Yang et al. (2012) and E. damingshanensis by Xiu and Yang (2017).In Kottelat's (2012) inventory of the loaches (Teleostei, Cypriniformes, Cobitoidei) of the world, 17 valid genera were included in the Gastromyzontidae.Nevertheless, its generic classification remains far from satisfactory mainly due to a poor understanding of the phylogenetic relationships within the family.Following 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 generic status (Chen et al. 2023).Erromyzon damingshanensis is reclassified in this study into a new genus of the Gastromyzontidae in China.
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 superficially most similar to E. damingshanensis but not conspecific with it or all other congeneric species, therefore representing an unrecognized species.Further morphological 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 opening 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. is also justified by its substantial genetic divergence (p-distances:10-12%) with phylogenetically allied genera Erromyzon and Yaoshania.The present study aims to propose a new genus Bashimyzon, with E. damingshanensis 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.

Specimen sampling and preservation
All specimens were collected in our field surveys conducted during 2020-2023, in accordance with the Chinese Laboratory Animal Welfare and Ethics animal welfare laws (GB/T35892-2018).Specimens were caught using electrofishing and/or trap nets.After being anaesthetized, 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 (IHB), Chinese Academy of Sciences, Wuhan City, Hubei Province, P. R. China.

Morphological and geometric morphometric analysis
Measurements, as depicted in Fig. 1, were made point-topoint 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 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 counted 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 vertebrae.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 photographed 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 ordinate 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 analyses were run using MorphoJ 1.07a software (Klingenberg 2011).A generalized Procrustes analysis (GPA) was conducted 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% ethanol-stored fin or muscle tissue samples using TIANamp Genomic DNA Kit (Tiangen Biotech Co., Ltd, Beijing, China) following manufactures' instructions.The mitochondrial cytochrome c oxidase subunit I (COI) gene was chosen for phylogenetic analysis.Two new pairs of specific primers were designed for amplification (COI_F: ATCCTACCTGTGGCAATCAC / COI_R: AATAGG-GGRAATCAGTGGAC) and sequencing (COI_F1: GCATCWGTAGACCTRACYATYTT / COI_R1: GCATARTATGCYACGACGTGRG) of the COI region in Bashimyzon and its close relatives.This gene was amplified by the polymerase chain reaction (PCR) in 25 µl reactions containing 12.5 µl Master mix Taq (Genesand Biotech Co. Ltd., Beijing, China), 1µl of each primer, 1µl template DNA and 9.5µl double distilled water (dd H 2 O).
The PCR conditions were given as follows: initial denaturation 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 5min.Amplified products were stored at 4 °C.The sequencing was done through Aokedingsheng Biotechnology Company (Wuhan, China).All sequences amplified in this study were submitted to GenBank.
The haplotype sequence matrix was used for subsequent 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 st codon with SYM+I, 2 nd with F81+I, and 3 rd with GTR+G.
Two independent runs were carried out with four Monte Carlo Markov chains (three hot chains and one cold chain) for 20 million generations to calculate posterior probability.Trees were sampled for every 1000 generations.The initial 25% of sampled trees were discarded as burn-in.Convergence of the runs was assessed by the average standard deviation of split frequencies (< 0.01).Partitioned maximum likelihood (ML) analyses were conducted in RAxMLHPC v7.0 (Stamatakis 2006) with the same partitioning strategy as for  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 estimated 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.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, extending 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 genera in having a larger (vs.small) gap between the posterior 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 Bashimyzon is morphologically most similar to Erromyzon, 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 extremity 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 (岜是), 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 "岜是鳅属".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    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.

Bashimyzon cheni
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.
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).

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 Boulenger, 1899, Katibasia Kottelat, 2004, Liniparhomaloptera Fang, 1935, Parhomaloptera Vaillant, 1902, Plesiomyzon Zheng & Chen, 1980and Vanmanenia Hora, 1932.These eight genera possess a large gill opening extending downwards beyond the pectoral-fin insertion to the ventral surface of head.The second group, comprising Paraprotomyzon s. str.and Yaoshania, have an intermediate gill opening extending downwards to but not beyond the pectoral-fin insertion to the ventral surface of head.The third group consists of Beaufortia Hora, 1932, Engkaria Tan, 2021, Gastromyzon Günther, 1874, Hypergastromyzon Roberts, 1989, Labigastromyzon Tang & Chen, 1996, Neogastromyzon Popta, 1905, Pseudogastromyzon Nichols, 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. damingshanensis (Xiu & Yang, 2017) and B. cheni here described.The former was previously placed in Erromyzon, a genus   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 identified species of Paraprotomyzon s.l., 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 pectoral-fin insertion.However, all other currently identified species of Paraprotomyzon, namely P. bamaensis Tang, 1997, P. lungkowensis Xie, Yang & Gong, 1984, P. niulanjiangensis 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 differences 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 represent their own genus, and Paraprotomyzon is 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 extending downwards close to but not beyond the pectoral-fin insertion (see Vaillant 1893;Hora andJayaram 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 andP. borneensis Hora &Jayaram, 1952.Given the generic-level taxonomic importance of gill-opening size revealed by Yang et al. (2012) and also in this study, P. whiteheadi and P. griswoldi 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 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 restricted only to a single stream.Their restricted distribution makes these rheophilic fishes susceptible to anthropogenic 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 agriculture.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 population (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, conservation 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 is 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 E. sinensis.

Figure 2 .
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 4 .
Figure 4. Comparisons (linear regression) of some morphometric measurements between sampled species of Erromyzon [E.sinensis (blue dot), E. compactus (green diamond), E. yangi (grey star), and E. kalotaenia (yellow triangle)] and Bashimyzon [B.damingshanensis (ponk dot) and B. cheni (red square)].A. Between GL% of HD and HD; B. Between G-P% of HD and HD; C. Between PPL% of SL and SL; and D. Between PBL% of SL and SL.GL-gill opening length; G-P-distance from the lowest extremity of gill opening to the pectoral-fin insertion; HD-head depth; PPL-pre-pectoral length; PBL-pectoral-fin base length; SL-standard length.

Figure 8 .
Figure 8. Scatterplots for the first two principal components (PC1 and PC2) 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).

Table 1 .
Detailed information of specimens used for molecular phylogenetic analyses in this study.

Table 2 .
Comparison of diagnostic characters among Bashimyzon gen.nov.and other related genera.

Table 4 .
(Yang et al. 2012)(uncorrected p-distance) of COI gene computed by MEGA v7.0 amongst 7 species of Erromyzon, Bashimyzon and Yaoshania.Chinese species formerly misidentified in Protomyzon and a new species of northeastern Vietnam(Kottelat 2004).Also misplaced in Protomyzon was the type species of Yaoshania in Chinese literature.FromKottelat'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 Cobitoidea.Our study demonstrated that Y. pachychilus had a minimum genetic distance of 11% with E. kalotaenia and E. sinensis for the COI gene.And the maximum genetic 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.l.slightly greater than the minimum one between Yaoshania and Erromyzon (11%) (Table