Integrative Taxonomic Evidence Supports a New Genus of Schizopygopsinae and a Redefinition of the Genus Gymnodiptychus (Cypriniformes, Cyprinidae) ^†

Abstract

Gymnodiptychus Herzenstein, 1892, a genus of the subfamily Schizopygopsinae, currently comprises three valid species: Gymnodiptychus dybowskii, Gymnodiptychus pachycheilus, and Gymnodiptychus integrigymnatus. Previous molecular phylogenetic studies have suggested that the genus is not monophyletic, but the taxonomic status of Gymnodiptychus integrigymnatus has not been comprehensively reassessed. In this study, we conducted an integrative taxonomic investigation of Gymnodiptychus based on mitochondrial genome data, combined with morphological and osteological evidence. Phylogenetic analyses using the concatenated sequences of 13 mitochondrial protein-coding genes and two ribosomal RNA genes recovered Gymnodiptychus as non-monophyletic. Gymnodiptychus dybowskii and Gymnodiptychus pachycheilus formed a monophyletic clade sister to Diptychus, whereas Gymnodiptychus integrigymnatus formed an independent lineage sister to Schizopygopsis. Genetic distance analyses further revealed substantial divergence between Gymnodiptychus integrigymnatus and other members of Gymnodiptychus. Morphological and osteological comparisons demonstrated that Gymnodiptychus integrigymnatus differs markedly from the other two species, Gymnodiptychus dybowskii and Gymnodiptychus pachycheilus, in lacking pectoral girdle scales, possessing extremely reduced maxillary barbels, having a terminal mouth, and lacking the supraorbital bone. Based on this combined evidence, we establish the new genus Gaoligongia gen. nov. for Gymnodiptychus integrigymnatus Mo, 1989, which is herein reassigned as Gaoligongia integrigymnata (Mo, 1989), comb. nov. We also provide a revised diagnosis of Gymnodiptychus and a key to the genera of Schizopygopsinae.

1. Introduction

Mountain barbels or snow barbels are the common term used to refer to a group of cyprinid fishes endemic to the Asian highlands. Their shared diagnostic character is the presence of anal scales, i.e., a row of enlarged specialized scales arranged on each side of the anus and anal-fin base [1]. In early taxonomic systems, these fishes were collectively assigned to the subfamily Schizothoracinae McClelland, 1842 within the family Cyprinidae Rafinesque, 1815 based on shared morphological traits such as the anal scales [1,2]. Subsequent molecular phylogenetic studies, however, divided the genera formerly included in Schizothoracinae into two distinct subfamilies: Schizothorax Heckel, 1838 and its close relatives were retained within Schizothoracinae, whereas Schizopygopsis Steindachner, 1866 and its allied genera were transferred to Schizopygopsinae Mirza, 1991 [3,4].

At present, Schizopygopsinae comprises five valid genera: Diptychus Steindachner, 1866, Gymnodiptychus Herzenstein, 1892, Oxygymnocypris Tsao, 1964, Ptychobarbus Steindachner, 1866, and Schizopygopsis. Among them, Gymnodiptychus currently contains three valid species [5]: the type species Gymnodiptychus dybowskii (Kessler, 1874), distributed in Central Asia (Kazakhstan and Kyrgyzstan) and Xinjiang Uyghur Autonomous Region of China; Gymnodiptychus pachycheilus Herzenstein, 1892, distributed in the upper reaches of the Yangtze and Yellow rivers in China; and Gymnodiptychus integrigymnatus Mo, 1989, as an endemic species in Gaoligong Mountain, distributed in the Irrawaddy River basin (upper Longchuanjiang and Dayingjiang rivers), as well as the upper Nujiang River drainage in Yunnan Province, China (Figure 1).

The distribution of Gymnodiptychus species is disjunct: Gymnodiptychus dybowskii is distributed in Central Asia, Xinjiang, and the northwestern Qinghai–Tibet Plateau, Gymnodiptychus pachycheilus occurs in the upper reaches of the Yangtze and Yellow Rivers in the eastern part of the Qinghai–Tibet Plateau, whereas Gymnodiptychus integrigymnatus is restricted to the Gaoligong Mountains region on the southwestern margin of the Qinghai–Tibet Plateau. Such distributional differences may indicate potential taxonomic problems within the group. Early morphological studies based on 41 osteological and external morphological characters supported the monophyly of Gymnodiptychus and suggested a close relationship with Ptychobarbus [6]. With the increasing application of molecular phylogenetics, however, the monophyly of the genus has been repeatedly questioned. He et al. [7], based on phylogenetic analyses of the Cyt b gene, were the first to reveal the non-monophyly of Gymnodiptychus. In that study, Gymnodiptychus integrigymnatus was recovered as more closely related to Schizopygopsis, whereas Gymnodiptychus dybowskii and Gymnodiptychus pachycheilus formed a monophyletic group closely related to Diptychus. Subsequent studies by Yang et al. [8], based on Cyt b and D-loop sequences, and Yang et al. [3], based on three nuclear and three mitochondrial genes, recovered results consistent with those of He et al. [7]. Therefore, the monophyly of Gymnodiptychus and the taxonomic status of Gymnodiptychus integrigymnatus require re-evaluation.

In the present study, we addressed the uncertain monophyly of Gymnodiptychus using an integrative approach combining phylogenetic, morphological, and osteological analyses. Based on mitochondrial genome data, we reassessed the phylogenetic positions of the three currently recognized species of Gymnodiptychus and established a new genus, Gaoligongia gen. nov., to accommodate Gymnodiptychus integrigymnatus, for which a comprehensive redescription is provided. This study offers new insights into the phylogenetic relationships within Schizopygopsinae and provides a taxonomic foundation for understanding the evolutionary mechanisms of this specialized high-altitude adaptive group.

2. Materials and Methods

2.1. Specimen Collection and Examination

A total of 15 specimens of Gaoligongia integrigymnata were collected from tributaries of the upper Longchuanjiang River in Mingguang and Jietou Town, Tengchong City, Yunnan Province, China, and from the Nandi River, an upper tributary of the Dayingjiang River in Beihai Town, Tengchong City (Figure 1). Fish were euthanized with an overdose of clove oil anesthetic, after which the right pectoral fin was removed and preserved in 95% ethanol for molecular analyses. Specimens were subsequently fixed in 10% formalin and later transferred to 75% ethanol for long-term preservation in the Kunming Natural History Museum of Zoology, Kunming Institute of Zoology (KIZ), Chinese Academy of Sciences, Kunming, Yunnan, China. To facilitate comparative morphological examinations, newly collected specimens of Gaoligongia integrigymnata, together with additional museum specimens of the species deposited in KIZ, were examined. Representative specimens of the remaining genera of Schizopygopsinae housed in KIZ were also examined to assess intergeneric morphological variation and diagnostic characters. In addition, morphological characters of some taxa for which specimens were unavailable were obtained from the literature. Terminology for morphological descriptions of schizopygopsine fishes mainly follows Chen & Chen [6]. No statistical analyses of morphometric data were conducted in this study, as the taxonomic conclusions were based primarily on discrete morphological, osteological, and molecular phylogenetic characters used for generic diagnosis and comparison.

2.2. Micro-CT Scanning

Micro-CT scanning of cranial osteological structures was conducted at Shanghai University. Specimens examined included three individuals of Gaoligongia integrigymnata (KIZGLGS05279, KIZGLGS05281, KIZGLGS05282), one individual of Gymnodiptychus dybowskii (KIZ2023000028), and two individuals of Gymnodiptychus pachycheilus (KIZ1982003653, KIZ1982003654). Specimens were scanned using a North Star Imaging system (maximum voltage 225 kV) (North Star Imaging Inc., Rogers, MN, USA) under the following parameters: 110 kV voltage, 80 μA current, 1080 projections, and a resolution range of 17–27 μm per pixel. The scanned images and associated data were processed using VG Studio Max v2.1 software as previously reported [9,10]. Descriptions of cranial osteological characters followed Zhao et al. [11] and Chen & Chen [6].

2.3. Mitochondrial Genome Sequencing, Assembly, and Annotation

One specimen of Gaoligongia integrigymnata was selected for mitochondrial genome sequencing. Total genomic DNA was extracted using the FastPure Cell/Tissue DNA Isolation Mini Kit-BOX (Vazyme Biotech Co., Ltd., Nanjing, China) following the manufacturer’s protocol. The extracted DNA was sequenced by Personalbio Biotechnology Co., Ltd. (Shanghai, China) on the Illumina NovaSeq platform with 2 × 150 bp paired-end reads. The mitochondrial genome was assembled using MitoZ 3.6 [12] with default parameters and subsequently annotated using the online platform MitoAnnotator v2026.06 [13].

2.4. Phylogenetic Analyses and Genetic Distances

For the phylogenetic analysis, we first ensured comprehensive representation of genera and species within Schizopygopsinae and Schizothoracinae. To this end, we downloaded nearly all available mitochondrial genome sequences for these two subfamilies from GenBank. We then conducted representative sampling of the remaining cyprinid subfamilies, generally including two representative species from each subfamily. Finally, a total of 61 mitochondrial genomes of Cyprinidae downloaded from NCBI, together with the newly generated mitochondrial genome in this study, were included as ingroup taxa (

Table 1. Taxa included in the phylogenetic analyses, with GenBank accession numbers, localities and drainage systems. An asterisk indicates that the data were obtained from this study.

Species	Accession No.	Locality	Drainage
Cyprinidae (Ingroups)
Acrossocheilinae
Acrossocheilus iridescens	AP011242	Van Quan, Lang Son, Vietnam	N/A
Folifer brevifilis	AP011354	Mae Hong Son, Thailand	N/A
Barbinae
Barbus barbus	AB238965	Lutzmansburg, Rabnitz, Austria	Danube River
Capoeta damascina	AP011183	N/A	N/A
Cyprininae
Carassioides acuminatus	AP011178	Vinh Phuc, Vietnam	Dai Lai Lake
Carassius auratus	KF147851	N/A	N/A
Labeoninae
Garra spilota	AP011327	N/A	N/A
Labeo senegalensis	AB238968	N/A	N/A
Probarbinae
Catlocarpio siamensis	AP011184	Kampong Chhnang, Cambodia	Mekong River
Probarbus jullieni	AP011187	Aquarium	Mekong River
Schizopygopsinae
Diptychus maculatus	KM659026	Xinjiang, China	Kunes River, Ili River
Gymnodiptychus dybowskii	KX688545	Xinjiang, China	Kaidu River, Kunes River
Gymnodiptychus dybowskii	MN422094	Xinjiang, China	Ili River
Gymnodiptychus pachycheilus	KT833111	N/A	N/A
Gymnodiptychus pachycheilus	KF976395	Luhuo, Sichuan, China	Xianshui River
Gaoligongia integrigymnata	PX503671	Tengchong, Yunnan, China	Longchuan River
Gaoligongia integrigymnata	PZ456618 *	Tengchong, Yunnan, China	Longchuan River
Oxygymnocypris stewartii	KT833083	N/A	N/A
Oxygymnocypris stewartii	KF528985	China	N/A
Ptychobarbus chungtienensis	KY012741	Shangri-La, Yunnan, China	Bita Lake
Ptychobarbus conirostris	KT833099	N/A	N/A
Ptychobarbus dipogon	KF597526	N/A	N/A
Ptychobarbus kaznakovi	KM268050	Baiyu, Sichuan, China	Ouqu River
Schizopygopsis anteroventris	KP641340	Zogong, Xizang, China	Yu Chu River
Schizopygopsis chengi	KM593242	Sichuan, China	Baoxing River
Schizopygopsis kessleri	MN857243	N/A	N/A
Schizopygopsis kialingensis	KT833101	N/A	N/A
Schizopygopsis pylzovi	KY511123	N/A	N/A
Schizopygopsis selincuoensis	MF787293	Xizang, China	Selincuo Lake
Schizopygopsis stoliczkai	KP641343	Pishan, Xinjiang, China	Karakash River, Tarim River
Schizothoracinae
Aspiorhynchus laticeps	KF564793	Xinjiang, China	Tarim River
Percocypris pingi	JX316026	Sichuan, China	Dadu River
Percocypris retrodorsalis	MW786772	China	N/A
Schizopyge curvifrons	PP778510	Kashmir, India	Dal Lake
Schizothorax argentatus	MZ958820	N/A	N/A
Schizothorax chongi	KJ718889	Sichuan, China	Yalong River
Schizothorax curvilabiatus	MF804977	N/A	N/A
Schizothorax dolichonema	KJ577589	N/A	N/A
Schizothorax esocinus	AP011412	Nepal	Ganges River
Schizothorax fedtschenkoi	PP375291	Uzbekistan	Amu Darya River
Schizothorax gobioides	PP375292	Uzbekistan	Amu Darya River
Schizothorax gongshanensis	KT946652	Gongshan, Yunnan, China	Nujiang River
Schizothorax gulinensis	OQ730545	Gulin, Sichuan, China	Baisha River, Chishui River
Schizothorax integrilabiatus	MG280782	N/A	N/A
Schizothorax kozlovi	KJ755668	N/A	N/A
Schizothorax lantsangensis	KT833095	N/A	N/A
Schizothorax macropogon	KT833087	N/A	N/A
Schizothorax nepalensis	AP011207	N/A	N/A
Schizothorax oconnori	KT833107	N/A	N/A
Schizothorax paoshanensis	KR780749	N/A	N/A
Schizothorax plagiostomus	KF928796	Baoshan, Yunnan, China	N/A
Schizothorax progastus	KF739399	Pauri Garhwal, Uttarakhand, India	Alaknand river
Schizothorax pseudoaksaiensis	KM079630	Xinjiang, China	Ili River
Schizothorax sinensis	MW191514	Bazhong, Sichuan, China	Jiaojiahe River
Schizothorax taliensis	MH094667	Dali, Yunnan, China	Erhai lake
Schizothorax waltoni	JX202592	Xizang, China	Yarlung Zangbo River
Smiliogastrinae
Puntius ticto	AB238969	Thailand	Mae Kok River
Rohtee ogilbii	AP011362	Aquarium	N/A
Spinibarbinae
Spinibarbus caldwelli	AP011376	Lang Son, Vietnam	N/A
Spinibarbus sinensis	KC579368	N/A	N/A
Torinae
Neolissochilus stracheyi	AP011252	Aquarium	N/A
Tor sinensis	KF305826	N/A	N/A
Psilorhynchidae (Outgroups)
Psilorhynchus balitora	AP011434	Aquarium	N/A
Psilorhynchus sucatio	AP011288	Aquarium	N/A

). In addition, two mitochondrial genomes of Psilorhynchidae downloaded from NCBI were selected as outgroups. Thirteen protein-coding genes (PCGs) and two ribosomal RNA genes were included in the analyses. Sequence alignment was conducted separately for each gene using MAFFT v7.505 [14,15] implemented in PhyloSuite v2 [16]. Terminal stop codons of all PCGs were manually removed prior to concatenation, and poorly aligned regions were trimmed using trimAl v1.2 [17]. The concatenated dataset was initially partitioned into 41 data blocks, corresponding to the three codon positions of each of the 13 PCGs (39 partitions) and the two ribosomal RNA genes (2 partitions). The optimal partitioning scheme and substitution models were selected using PartitionFinder v2.1.1 [18] under the corrected Akaike Information Criterion (AICc) using the greedy search. Maximum likelihood (ML) analyses were performed using IQ-TREE v2.2.0 [19], with nodal support assessed by 5000 ultrafast bootstrap replicates [20]. Bayesian inference (BI) analyses were conducted in MrBayes v3.2.7 using two independent runs with four Monte Carlo Markov chains for 10,000,000 generations [21]. Convergence was assessed in Tracer v1.7.1 [22], and all effective sample size (ESS) values exceeded 200. Phylogenetic trees were visualized and edited using iTOL v7.2 [23]. Pairwise genetic distances were calculated in MEGA X v10.2.2 based on the concatenated sequences of the 13 mitochondrial protein-coding genes using the Kimura two-parameter (K2P) model with 1000 bootstrap replicas [24,25]. The K2P model was selected because it accounts for different rates of transitions and transversions and has been widely used in taxonomic and systematic studies of fishes, facilitating comparisons with previously published studies.

2.5. Distribution Mapping

Distribution localities of Gaoligongia integrigymnata, Gymnodiptychus dybowskii, and Gymnodiptychus pachycheilus were compiled from specimens collected in this study and historical records, including examined specimens deposited in the Kunming Institute of Zoology (KIZ), published records (e.g., [1,2]), and occurrence records downloaded from the Global Biodiversity Information Facility (GBIF.org; https://doi.org/10.15468/dl.zehuab, accessed on 25 May 2026). Duplicate records and records lacking reliable locality information were excluded prior to analysis. Distribution maps were generated using ArcMap v10.8 (ESRI, Redlands, California, USA) and the basemap was from the Resource and Environmental Science Data Platform, https://www.resdc.cn/ (accessed on 26 May 2026).

3. Results

3.1. Systematic Account

Family Cyprinidae Rafinesque, 1815

Subfamily Schizopygopsinae Mirza, 1991

Genus Gaoligongia gen. nov.

Figure 2a,b, Figure 3a, Figure 4a,b and Figure 5a

Type species. Gymnodiptychus integrigymnatus Mo, 1989.

Diagnosis. Gaoligongia gen. nov. can be distinguished from other genera of Schizopygopsinae by the following combination of characters: (1) pectoral girdle scales absent (vs. pectoral girdle scales present in Diptychus, Ptychobarbus, Oxygymnocypris, Schizopygopsis and Gymnodiptychus); (2) one pair of extremely reduced barbels, with barbel length less than 25% of eye diameter (vs. barbels absent in Schizopygopsis and Oxygymnocypris; one pair of well-developed barbels equal to or longer than eye diameter in Diptychus, Ptychobarbus, and Gymnodiptychus); (3) mouth terminal (share with Oxygymnocypris vs. inferior in Diptychus, Ptychobarbus, and Gymnodiptychus; inferior or subterminal in Schizopygopsis); (4) anterior margin of lower jaw without a sharp keratinized cutting edge (vs. anterior margin of lower jaw with a sharp keratinized cutting edge in Diptychus; anterior margin of lower jaw with or without a sharp keratinized cutting edge in Schizopygopsis); and (5) supraorbital bone absent (vs. supraorbital bone present in Diptychus, Ptychobarbus, Oxygymnocypris, Schizopygopsis and Gymnodiptychus).

Description. Body elongate, with the anterior portion cylindrical and the posterior portion slightly compressed laterally; dorsal profile elevated and abdomen rounded. Snout rounded and blunt. Mouth terminal, with an arcuate gape. Anterior margin of lower jaw slightly keratinized but not forming a sharp edge. Lower lip weakly developed, divided into two narrow lateral fleshy lobe on both sides of the lower jaw, weakly connected anteriorly. Posterior groove of lower lip interrupted, restricted to the corners of the mouth. One pair of maxillary barbels present, extremely reduced with barbel length less than 25% of eye diameter. Lateral line complete, with only a few anterior lateral-line scales exposed externally, usually less than 20, whereas the remaining lateral-line scales are embedded beneath the skin. Pectoral girdle scales absent. Axillary scales present at the base of pelvic fin. Two rows of anal scales present. Remaining body entirely naked. Dorsal fin iii,8; last unbranched dorsal-fin ray soft and smooth; dorsal-fin origin anterior to pelvic-fin origin. Anal fin iii,5. Two rows of pharyngeal teethw ith pointed and slightly hooked tips and spoon-shaped grinding surfaces; dentition 3.4–4.3. Supraorbital bone absent. Air bladder two-chambered. Body sides densely covered with dark brown spots.

Distribution. This genus is distributed in the upper Longchuanjiang River and upper Dayingjiang River (Irrawaddy River basin) on the western slope of the Gaoligong Mountains, as well as in the Nujiang River drainage on the eastern slope of the Gaoligong Mountains in Yunnan Province, China (Figure 1).

Etymology. Gaoligongia is named after the Gaoligong Mountains, a major mountain range in the Hengduan Mountains region of southwestern China, which represents the known distribution area of this genus. The suffix -ia is a commonly used feminine Latin ending for generic names in zoological nomenclature. The name refers to the endemic occurrence of this lineage in the Gaoligong Mountains region. We propose the Chinese common name “高黎贡鱼属” (Gāo Lí Gòng Yú Shǔ) for this new genus and the Chinese name “全裸高黎贡鱼” (Quán Luǒ Gāo Lí Gòng Yú) for the type species Gaoligongia integrigymnata.

Species included. Gaoligongia integrigymnata (Mo, 1989), comb. nov. (type species).

Remarks. Gaoligongia integrigymnata was originally mentioned in 1981 by Cao et al. [26] as Gymnodiptychus integrigymnatus, with the species name attributed to Shunyou Huang. However, the name was not accompanied by a formal diagnosis and therefore constitutes a nomen nudum under Articles 13.1.1 and 13.1.2 of the International Code of Zoological Nomenclature (ICZN). Subsequently, Mo provided the first available description of the species in 1989 [27], although the authorship was still attributed therein to Huang in Cao et al. [26]. Huang later redescribed the species as Gymnodiptychus integrigymnatus in The Fishes of the Hengduan Mountains Region in 1998 [28]. Yang et al. [29] clarified the nomenclatural history of the taxon and demonstrated that the correct authorship should be Gymnodiptychus integrigymnatus Mo, 1989. They further recognized 13 syntypes deposited in KIZ based on the material examined by Mo [27]. The present study transfers this species to the new genus Gaoligongia gen. nov. based on both molecular phylogenetic and morphological evidence. This new genus is established in accordance with the provisions of Articles 13 and 16 of the International Code of Zoological Nomenclature (ICZN). The species-group name integrigymnatus is herein treated as an adjectival epithet; accordingly, its ending is modified to agree with the feminine gender of the generic name Gaoligongia, resulting in the new combination Gaoligongia integrigymnata (Mo, 1989), comb. nov.

The present study also records Gaoligongia integrigymnata from the Nandi River, an upper tributary of the Dayingjiang River in Tengchong City, Yunnan Province, for the first time, thereby extending the known distribution of the species (Figure 1).

The transfer of Gymnodiptychus integrigymnatus to the new genus Gaoligongia alters the original diagnostic concept of Gymnodiptychus. Consequently, a revised diagnosis and description of Gymnodiptychus are provided below based on the remaining two valid species, Gymnodiptychus dybowskii and Gymnodiptychus pachycheilus.

Genus Gymnodiptychus Herzenstein, 1892

Figure 2c,d, Figure 3b,c, Figure 4c,d and Figure 5b,c

Gymnodiptychus Herzenstein, 1892: 225. Type species: Diptychus dybowskii Kessler, 1874.

Diagnosis. Gymnodiptychus can be distinguished from Gaoligongia gen. nov. by having well-developed maxillary barbels, equal to or longer than eye diameter (vs. extremely reduced maxillary barbels, barbel length less than 25% of eye diameter), an inferior mouth (vs. terminal), supraorbital bones present (vs. absent), and pectoral girdle scales present (vs. absent).

Gymnodiptychus can be further distinguished from other genera of Schizopygopsinae by the following combination of characters: one pair of barbels present (vs. barbels absent in Schizopygopsis and Oxygymnocypris); body largely naked except for lateral-line scales, pectoral girdle scales, anal scales, and axillary pelvic scales (vs. body completely covered with scales on the dorsum and flanks in Diptychus and Ptychobarbus); and anterior margin of lower jaw without a sharp keratinized cutting edge (vs. anterior margin of lower jaw with a sharp keratinized cutting edge in Diptychus; anterior margin of lower jaw with or without a sharp keratinized cutting edge in Schizopygopsis).

Description. Body elongate, anterior portion cylindrical and posterior portion slightly compressed laterally. Mouth inferior, with a horseshoe-shaped gape. Anterior margin of lower jaw lacking a keratinized edge. Lower lip well developed, divided into two lateral fleshy lobes connected anteriorly, smooth and lacking papillae on the surface; posterior groove of lower lip continuous or interrupted. One pair of maxillary barbels present, longer than eye diameter. Lateral line complete, comprising more than 80 scales. Several irregular rows of scales present on the pectoral girdle; axillary scales present at pelvic-fin base; two rows of anal scales present; remaining body naked. Dorsal fin iii,8; last unbranched ray soft and smooth. Anal fin iii,5. Two rows of pharyngeal teeth with slightly hooked tips and spoon-shaped grinding surfaces; dentition 3.4–4.3. Supraorbital bone present. Air bladder two-chambered. Body with numerous spots.

Distribution. This genus is distributed in the upper reaches of the Yangtze and Yellow rivers and Xinjiang Uyghur Autonomous Region in China, as well as in Central Asia (Kazakhstan and Kyrgyzstan) (Figure 1).

Etymology. “Gymno-” comes from the Greek word “gymnós”, meaning naked or bare; “diptychus” refers to the genus Diptychus in which the type species was originally placed. The generic name refers to the reduction of body scales in species of this genus, with the body largely naked except for the lateral-line scales and several specialized scale patches. The generic name in Chinese is “裸重唇鱼属” (Luǒ Chóng Chún Yú Shǔ).

Species included. Gymnodiptychus dybowskii (Kessler, 1874); Gymnodiptychus pachycheilus Herzenstein, 1892.

3.2. Molecular Phylogenetic Analyses

In this study, the mitochondrial genome of Gaoligongia integrigymnata was newly sequenced and assembled as a complete circular molecule with a total length of 17,160 bp. The overall A+T content was 60.0%. The mitogenome contained the full complement of 37 mitochondrial genes, including 13 protein-coding genes (PCGs), 22 transfer RNA genes (tRNAs), and 2 ribosomal RNA genes (rRNAs), together with a control region, indicating a complete mitochondrial genome assembly. The assembled mitochondrial genome sequence and its annotation have been deposited in GenBank under accession number PZ456618.

Based on the concatenated dataset of 13 mitochondrial protein-coding genes and two ribosomal RNA genes (14,000 bp in total), phylogenetic analyses were conducted using two sequences from Psilorhynchidae as outgroups and 62 sequences from Cyprinidae as ingroups, including 20 sequences representing 16 species of Schizopygopsinae (Table 1). The optimal partitioning scheme selected by PartitionFinder merged the 41 initial data blocks into 22 partitions (

Table A1. Partitioning scheme and best-fit substitution models selected by PartitionFinder for the mitochondrial dataset used in phylogenetic analyses. Codons 1–3 indicate the first, second, and third codon positions of protein-coding genes, respectively.

Partition	Included Data Blocks	Length (bp)	Best-Fit Model
P1	nad3 codon1, nad4 codon1, atp6 codon1	803	GTR+I+G
P2	nad4 codon2, atp6 codon2, nad4L codon2	785	GTR+I+G
P3	nad3 codon3, atp6 codon3	343	GTR+I+G
P4	nad5 codon1, atp8 codon1	661	GTR+I+G
P5	atp8 codon2, nad5 codon2	661	GTR+I+G
P6	cox2 codon3, atp8 codon3	284	GTR+I+G
P7	nad4L codon1, cox1 codon1	614	GTR+I+G
P8	cox1 codon2	516	GTR+I+G
P9	cox1 codon3	516	GTR+I+G
P10	cox2 codon1, cytb codon1, nad1 codon1	934	GTR+I+G
P11	cox2 codon2, cox3 codon2, cytb codon2	871	GTR+I+G
P12	cox3 codon1	261	SYM+I+G
P13	cox3 codon3	261	GTR+I+G
P14	nad5 codon3, nad4L codon3, cytb codon3	1085	GTR+I+G
P15	nad1 codon2, nad3 codon2	440	GTR+I+G
P16	nad2 codon3, nad1 codon3, nad4 codon3	1132	GTR+I+G
P17	nad2 codon1	348	GTR+I+G
P18	nad2 codon2	348	GTR+I+G
P19	nad6 codon1	173	GTR+I+G
P20	nad6 codon2	173	HKY+I+G
P21	nad6 codon3	173	GTR+I+G
P22	rrnL, rrnS	2618	GTR+I+G

). Among these, 20 partitions were assigned the GTR+I+G model, whereas one partition was assigned the SYM+I+G model and one partition the HKY+I+G model. Maximum likelihood (ML) and Bayesian inference (BI) trees were reconstructed separately (Figure 6). The topologies of the ML and BI trees were largely congruent. All species of Schizopygopsinae formed a well-supported monophyletic group, which was recovered as sister to Barbinae (maximum-likelihood bootstrap values, BP = 92, Bayesian posterior probabilities, PP = 1); this larger clade was in turn sister to Schizothoracinae (BP = 90, PP = 1). Within Schizopygopsinae, all genera were recovered as monophyletic. Within Gymnodiptychus, the type species Gymnodiptychus dybowskii and Gymnodiptychus pachycheilus formed a clade sister to Diptychus (BP = 100, PP = 1). Within the new genus Gaoligongia, Gaoligongia integrigymnata formed an independent lineage sister to Schizopygopsis (BP = 100, PP = 1).

We further calculated genetic distances based on the concatenated sequences of the 13 protein-coding genes for all schizopygopsine taxa included in the phylogenetic analyses (

Table 2. Average genetic distances among genera of Schizopygopsinae based on the K2P model. Values are presented as mean ± SD. Values in parentheses indicate average interspecific genetic distances within genera.

	1	2	3	4	5	6
1 Diptychus
2 Gymnodiptychus (0.116)	0.182 ± 0.004
3 Gaoligongia gen. nov.	0.203 ± 0.005	0.201 ± 0.004
4 Oxygymnocypris	0.185 ± 0.005	0.187 ± 0.004	0.144 ± 0.004
5 Ptychobarbus (0.057)	0.186 ± 0.004	0.183 ± 0.004	0.170 ± 0.004	0.141 ± 0.004
6 Schizopygopsis (0.053)	0.176 ± 0.004	0.179 ± 0.004	0.124 ± 0.003	0.108 ± 0.003	0.137 ± 0.003

). Within Schizopygopsinae, the average genetic distances among previously recognized genera range from 10.8% to 18.7%. In contrast, the genetic distances between Gaoligongia gen. nov. and the remaining genera range from 12.4% to 20.3%, encompassing and in some cases exceeding the range observed among currently recognized genera. The average genetic distance between Gaoligongia gen. nov. and Gymnodiptychus was 20.1%.

3.3. Key to the Genera of the Subfamily Schizopygopsinae

1a. Dorsum and flanks completely covered with scales ...................................................2

1b. Dorsum and flanks largely naked, scales absent over most of body .........................3

2a. Lower jaw with a sharp keratinized cutting edge .........................................Diptychus

2b. Lower jaw without a sharp keratinized cutting edge .............................Ptychobarbus

3a. Barbels absent ..................................................................................................................4

3b. One pair of barbels present ............................................................................................5

4a. Pelvic-fin origin at or posterior to vertical through dorsal-fin origin, snout not elongate.....................................................................................................................Schizopygopsis

4b. Pelvic-fin origin anterior to vertical through dorsal-fin origin, snout pointed and elongate..................................................................................................................Oxygymnocypris

5a. Pectoral girdle scales present, mouth inferior, supraorbital bone present....................................................................................................................Gymnodiptychus

5b. Pectoral girdle scales absent, mouth terminal, supraorbital bone absent..............................................................................................................Gaoligongia gen. nov.

4. Discussion

In previous studies, Gaoligongia integrigymnata was assigned to Gymnodiptychus primarily because it shares two diagnostic features with that genus: the body is largely naked except for the anal scales and axillary pelvic scales, with only a few scales occasionally present near the pectoral girdle region, and a single pair of maxillary barbels is present (see the keys in [1,27,28,30]). However, the squamation and the length of the barbels also represent the most conspicuous differences between Gaoligongia gen. nov. and Gymnodiptychus. Species of Gymnodiptychus possess several irregular rows of pectoral girdle scales, whereas pectoral girdle scales are completely absent in Gaoligongia gen. nov (Figure 4). In addition, the maxillary barbels of Gaoligongia gen. nov. are extremely reduced and much shorter than the eye diameter, whereas those of Gymnodiptychus are well developed, robust, and distinctly longer than the eye diameter (Figure 3). Apart from these differences, Gaoligongia gen. nov. can be readily distinguished from Gymnodiptychus by its terminal mouth (vs. inferior mouth) (Figure 2) and weakly developed lower-lip lobes (vs. well-developed lower-lip lobes) (Figure 3). Considerable differences in body size are also evident between the two genera. Based on the specimens examined in the present study (see Comparative materials), together with historical records [1,8,27,28,30], adults of Gaoligongia gen. nov. appear to attain a maximum standard length of approximately 129.0 mm and are usually less than 100 mm SL. In contrast, Gymnodiptychus pachycheilus may reach up to 580.0 mm SL, whereas Gymnodiptychus dybowskii can attain 295.0 mm SL [1,2,30]. Based on available field observations and collection records, species of Gaoligongia typically inhabit small headwater streams in mountainous areas, whereas species of Gymnodiptychus are generally associated with larger rivers and lakes. The relatively restricted habitat space and potentially lower food resource availability in headwater environments may have contributed to the smaller body size of Gaoligongia, although this hypothesis requires further ecological investigation. Osteologically, Gaoligongia gen. nov. can be directly distinguished from Gymnodiptychus by the absence of the supraorbital bone (vs. supraorbital bone present) (Figure 5). Collectively, these morphological and osteological differences, together with the phylogenetic evidence presented herein, strongly support the recognition of Gaoligongia as a distinct genus.

The intergeneric relationships within Schizopygopsinae recovered in the present study (Figure 6), as well as the relationships among Schizopygopsinae and other cyprinid subfamilies, are largely congruent with those reported in previous studies (e.g., [3,7,8,31]). This consistency is likely attributable to the widespread use of mitochondrial gene sequences in these analyses. Nevertheless, phylogenetic inference based solely on mitochondrial genomes has inherent limitations, including the potential effects of introgression, incomplete lineage sorting, and mito-nuclear discordance. These issues may be particularly relevant in Schizopygopsinae and related schizothoracine fishes, many of which have undergone polyploidization during their evolutionary history. Future studies incorporating nuclear markers and genome-scale datasets will therefore be essential for further testing the phylogenetic placement of Gaoligongia gen. nov.

Cao et al. [26] divided Schizothoracinae sensu lato (including both Schizothoracinae and Schizopygopsinae as recognized in the present study) into three specialization grades. The Primitive Grade (PG) is characterized by scales covering the entire body or being only partially reduced, three rows of pharyngeal teeth, and two pairs of barbels (occasionally one pair in some genera), and includes Schizothorax, Aspiorhynchus Kessler, 1879, and Schizopyge Heckel, 1847. The Specialized Grade (SG) is characterized by partial or complete scale reduction, two rows of pharyngeal teeth, and one pair of barbels, and includes Diptychus, Ptychobarbus, and Gymnodiptychus. The Highly Specialized Grade (HSG) is characterized by complete scale reduction, two rows of pharyngeal teeth (or one row in some genera), and absence of barbels, and includes Schizopygopsis and Oxygymnocypris. When interpreted in light of the phylogenetic results presented here, the PG taxa form a monophyletic lineage corresponding to Schizothoracinae (Figure 6). Within this lineage, Aspiorhynchus and Schizopyge are nested within Schizothorax. In addition, Percocypris Chu, 1935, a genus only recently assigned to Schizothoracinae [3], possesses scales covering the entire body, three rows of pharyngeal teeth, and two pairs of barbels, and therefore conforms well to the morphological characteristics of the PG. Consequently, Schizothoracinae as currently recognized appears to consist entirely of PG taxa.

In contrast, both SG and HSG taxa are placed within Schizopygopsinae (Figure 6). Phylogenetically, the SG taxa are divided into two distinct lineages. One lineage comprises Diptychus and Gymnodiptychus, whereas the other is represented by Ptychobarbus, which forms the basal branch of a larger clade containing Gaoligongia gen. nov., Oxygymnocypris, and Schizopygopsis. Within Schizopygopsinae, there is an overall trend from SG forms at the base toward increasingly specialized HSG forms in more derived positions. Notably, Gaoligongia gen. nov. exhibits a unique combination of characters. It retains several features typical of SG taxa, including the presence of a pair of maxillary barbels, although these are extremely reduced, and two rows of pharyngeal teeth with a dentition formula of 3.4–4.3. At the same time, it exhibits characters approaching those of HSG taxa, including a more extensive reduction of body scales and the complete loss of pectoral girdle scales. Consequently, Gaoligongia gen. nov. appears to represent an intermediate morphological condition between the Specialized Grade and the Highly Specialized Grade, providing important insights into the evolutionary transition between these two stages.

The evolutionary history and specialization processes of Schizopygopsinae, together with those of the closely related Barbinae and Schizothoracinae, remain highly significant topics for future research. Although substantial progress has been made in recent years (e.g., [32,33,34]), many aspects of the diversification, adaptation, and evolutionary history of these remarkable highland fishes remain poorly understood and warrant further investigation. The restriction of Gaoligongia to the Gaoligong Mountains region, together with its distinct phylogenetic position within Schizopygopsinae, suggests a potentially unique evolutionary history. As a biodiversity hotspot and a major watershed separating the Irrawaddy and Nujiang river systems, the Gaoligong Mountains may have promoted both the diversification and long-term persistence of endemic freshwater fish lineages. However, the historical processes responsible for the origin and isolation of Gaoligongia remain unclear. Future studies incorporating divergence-time estimation and historical biogeographic analyses will be necessary to evaluate the potential influence of regional geological events, including the uplift and drainage reorganization associated with the Qinghai–Tibet Plateau.

5. Comparative Materials

Gaoligongia integrigymnata: China: Irrawaddy River basin: KIZ1976001224–1228, KIZ1978001383–1390, syntype, 13 ex., 73.2–106.6 mm SL, Mingguang Town, Tengchong, Yunnan, 1976 and 1978; KIZ200309627, KIZ200309629–634, KIZ200309639–640, 9 ex., 67.7–99.1 mm SL, Zizhi, Tengchong, Yunnan, 28 September 2003; KIZ2020001544–1552, 9 ex., 31.9–76.8 mm SL, upper Jietou River, Datang Village, Jietou Town, Tengchong, Baoshan, Yunnan, 28 July 2020; KIZ2020000656–0660, 5 ex., 29.7–56.7 mm SL, Kongshu River, Mingguang Town, Tengchong, Baoshan, Yunnan, 26 July 2020; KIZ05282, 1 ex., 119.1 mm SL, Qushi, Tengchong, Baoshan, Yunnan, April 2006; KIZGLGS05279–282, 4 ex., 101.9–122.1 mm SL, Qushi, Tengchong, Baoshan, Yunnan, April 2006; KIZ2025005178, 1 ex., 103.8 mm SL, Nandi River, Beihai Town, Tengchong, Baoshan, Yunnan, 6 January 2026; Nujiang River basin: KIZ200310741–771, 30 ex., 40.6–99.4 mm SL, Manggang River, Baihualing, Baoshan, Yunnan, 7 October 2003; KIZGLGS07378, 1 ex., 119.0 mm SL, Zaotang River, Baihualing, Baoshan, Yunnan, April 2006; KIZGLGS05229–231, 3 ex., 98.9–124.7 mm SL, Manggang River, Baihualing, Baoshan, Yunnan, 25 April 2004; KIZGLGS07358–363, 6 ex., 79.2–110.7 mm SL, Manggang River, Baihualing, Baoshan, Yunnan, April 2006.

Gymnodiptychus dybowskii: China: KIZ2023000028, 1 ex., 162.4 mm SL, Yili, Xinjiang, 2006.

Gymnodiptychus pachycheilus: China: KIZ1982003653–3654, 2 ex., 176.4–196.3 mm SL, Juewu Monastery, Shiqu County, Sichuan, 8 September 1982; KIZ2010000268, 1 ex., 79.3 mm SL, locality unknown, 28 January 2010; KIZ1982002115–2133, 19 ex., 73.7–214.9 mm SL, Hongyuan County, Sichuan, 1982.

Ptychobarbus conirostris: China: KIZ1974000329, 1 ex., 160.7 mm SL, Shiquan River, Xizang, July 1974.

Schizopygopsis firmispinata: China: KIZ2009003608–3609, 2 ex., 74.2–167.4 mm SL, Jinsha River, Tuoding, Shangri-La, Yunnan, 19 September 2009.

Schizopygopsis malacanthus: China: KIZ2009003257–3271, 15 ex., 121.8–183.0 mm SL, Mudaocheng River, Daocheng County, Sichuan, 15 September 2009.

Diptychus maculatus: China: KIZ2023000024, KIZ2023000018, KIZ2023000022, 3 ex., 182.8–232.8 mm SL, locality and date unknown.

Oxygymnocypris stewartii: China: KIZ2023000027, 1 ex., 305.4 mm SL, Lhasa, Xizang, 2015.