Zoosyst. Evol. 101 (2) 2025, 465-471 | DOI 10.3897/zse.101.136965 yee BERLIN Description of a new loach species, Yunnanilus triangulus sp. nov. (Cypriniformes, Nemacheilidae), from Yunnan, China Mei Liu! *", Jian-Bing Lyu**, Li-Na Du! ?, Xiao-Yong Chen? 1 Key Laboratory of Ecology of Rare and Endangered Species and Environmental Protection, Guangxi Normal University, Ministry of Education, Guilin, Guangxi 541004, China 2 Guangxi Key Laboratory of Rare and Endangered Animal Ecology, College of Life Sciences, Guangxi Normal University, Guilin, Guangxi 541004, China 3 Kunming Natural History Museum of Zoology, Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming, Yunnan, 650223, China https://zoobank. org/0D26F007-FE9F-47B8-A 7F 2-6 DF23B3FA8 12 Corresponding authors: Li-Na Du (dulina@mailbox.gxnu.edu.cn); Xiao- Yong Chen (chenxy@mail.kiz.ac.cn) Academic editor: Nicolas Hubert @ Received 12 September 2024 Accepted 16 January 2025 Published 26 February 2025 Abstract A new species of the genus Yunnanilus, designated Yunnanilus triangulus sp. nov., is described from the Nanpan River in Yunnan Province, southwestern China. Nuptial males of this species are distinguished by the presence of tubercles on the caudal peduncle during the reproductive period, a feature not observed in other members of the genus. The new species is further characterized by the following unique combination of morphological characters: body scaled, smaller eyes than interorbital width, nine inner gill rakers on first gill arch, lateral head length 27.1%-30.9% SL, head width 14.3%-17.2% SL, eye diameter 19.6%-—23.8% of lateral head length, and caudal peduncle depth 94.0%—130.6% of its length. Morphological and molecular evidence support the validity of this species, despite its geographic proximity to Y. polylepis. These findings underscore the ecological specialization that exists within the genus Yunnanilus and highlight the urgent need for species-specific conservation strategies, given their restricted distributions and dependence on specific habitats. Key Words Caudal peduncle with tubercles, freshwater fish, morphological characters, sexual dimorphism Introduction Y. pleurotaenia species groups, based on the presence or absence of lateral and cephalic lateral line pores. Du et al. Nichols (1925) designated Nemacheilus pleurotaenia Re- gan, 1904, as the type species of the nemacheilid loach sub- genus Yunnanilus, with the following defining characters: short and compressed body, small scales, incomplete lateral line, slightly forked caudal fin, nostrils separated by greater distance than between posterior nostril and eye, and ante- rior nostril forming flap-like tube. Subsequently, Kottelat and Chu (1988) elevated Yunnanilus to the rank of genus, while Yang and Chen (1995) later categorized Yunnanilus species into two major assemblages, Y. nigromaculatus and * These authors contributed equally to this work. (2021) retained the ¥. pleurotaenia group within Yunnanilus but reassigned the Y. nigromaculatus group to the revalidat- ed genus Eonemachilus Berg, 1938. A more recent phylo- genetic analysis of Chinese nemacheilids with tube-shaped anterior nostrils by Du et al. (2023) confirmed the generic status of Yunnanilus and refined its diagnostic characters to mouth inferior; anterior and posterior nostrils separated, an- terior nostrils tube-like, without elongated barbel-like struc- ture; cheeks scaleless; lips with furrows; and lateral line and cephalic lateral line pores present (Du et al. 2021, 2023). Copyright Liu, M. et al. This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distri- bution, and reproduction in any medium, provided the original author and source are credited. 466 Currently, Yunnanilus comprises 20 valid species, all restricted to lakes, marshes, and slow-flowing waters within Yunnan and Sichuan Provinces of southwestern China (Qin et al. 2024). Among these, six species are dis- tributed in the Yangtze River system, including Y. discol- oris Zhou & He, 1989, Y. longibulla Yang, 1990, Y. pleu- rotaenia (Regan, 1904), and Y. spanisbripes An, Liu & Li, 2009 in the Jinsha River; Y. sichuanensis Ding, 1995 in the Yalong River; and Y. jiuchiensis Du, Hou, Chen & Yang, 2018 in the Tuo River; and 13 species are distribut- ed in the Pearl River basin, including Y. beipanjiangensis Li, Mao & Sun, 1994 in the Beipan River; Y. analis Yang, 1990; ¥. chui Yang, 1991; Y. elakatis Cao & Zhu, 1989; Y. forkicaudalis Li, 1999; Y. macrogaster Kottelat & Chu, 1988; Y¥. macrolepis Li, Tao & Mao, 2000; Y. macrosita- nus Li, 1999; Y¥. nanpanjiangensis Li, Tao & Lu, 1994; Y. paludosus Kottelat & Chu, 1988; ¥. parvus Kottelat & Chu, 1988: Y¥. polylepis Qin, Shao, Du & Wang, 2024; and Y. yangi He et al., 2024 in the Nanpan River, and one spe- cies, ¥. chuanheensis Jiang, Zhao, Du & Wang, 2021 in the Red River (Lixian River) (Du et al. 2021; Qin et al. 2024). In April 2018, eight specimens of Yunnanilus were col- lected from a tributary of the Nanpan River in Huaning County, Yuxi City, Yunnan Province, China. Morphological and molecular analyses confirmed that these specimens rep- resent a previously undescribed member of the genus, which is herein described and compared with all known congeners. Materials and methods All care and handling of experimental animals complied with the relevant laws of the Chinese Laboratory of Ani- mal Welfare and Ethics (GB/T 35892-2018). Upon their collection, all specimens were rapidly euthanized by an overdose of anesthetic clove oil. The right-side pelvic fins of five individuals were removed and preserved in 99% ethanol for molecular analyses, and eight individu- als were stored in 10% formalin for morphological com- parisons. The specimens were deposited in the Kunming Natural History Museum of Zoology, Kunming Institute of Zoology (KIZ), Chinese Academy of Sciences (CAS). All counts and measurements followed the methodolo- gy described by Kottelat (1990). Initial data processing and preliminary statistical analyses were performed using Excel software. Genomic DNA was extracted from ethanol-pre- served fin tissue, and partial sequences of the mitochondri- al cytochrome c oxidase subunit I (COI) and cytochrome b (Cyt 5) were sequenced by Tsingke Biotechnology Co., Ltd. (China). All sequences were assembled using SeqMan within the DNAStar package and aligned using MEGA vl1.0 (Tamura et al. 2021). Sequences were submitted to GenBank (Accession Nos. PQ300642—PQ300646 for COL PQ306053—PQ306057 for Cyt 5). The phylogenetic posi- tion of Yunnanilus triangulus sp. nov. was determined us- ing maximum-likelihood (ML) and Bayesian inference (BI) methods via the CIPRES Science Gateway (Miller et al. 2010). The ML tree was constructed using RAxML-HPC v8 zse.pensoft.net Liu, M. et al.: A new species of Yunnanilus (Stamatakis 2014) with a rapid bootstrapping configuration and 1000 bootstrap iterations. The BI tree was constructed using MrBayes in XSEDE v3.2.7a (Ronquist et al. 2012), with two simultaneous runs of four Markov chains starting from arandom tree. The chains were run for five million gen- erations and sampled every 100 generations. The first 25% of sampled trees were discarded as burn-in, and the remain- ing trees were used to generate a consensus tree and estimate Bayesian posterior probabilities (BPPs). The resulting phy- logenetic trees were viewed and edited using Figtree v1.4.4. Results Yunnanilus triangulus sp. nov. https://zoobank.org/228876CA-206D-4960-BC2E-4B 1692267979 Holotype. * KIZ2018002410 female, 51.8 mm standard length (SL), Dalongtan Spring, Wangma Village, Huan- ing County, Yuxi City, Yunnan, P.R. China; Nanpan Riv- er, 24.1716°N, 102.9182°E, 1619 m as.l., X.Y. Chen, L.L. Xu, and H.D. Lyu, collected April 2018. Paratypes. ° Seven — specimens. Female: KIZ2018002404, 2406-2407, 2409, 2411, 38.9-54.6 mm SL; Male: KIZ2018002405, KIZ2018002408, 37.1- 39.1 mm SL; same as holotype. Etymology. The specific name triangulus is derived from the unique presence of a tubercle on the caudal pe- duncle in nuptial males, a character not previously re- corded in the genus Yunnanilus. We suggest the Chinese vernacular name “= ff zs Fa ff” and the English vernac- ular name “triangle Yunnan loach.” Gender: masculine. Diagnosis. The new species can be distinguished from all other members of the genus by the presence of a unique triangular tubercle on the male caudal peduncle. It shares a body covered by scales, except on head and thorax, with Y. chuanheensis, Y. jiuchiensis, Y. longibulla, Y. macrogaster, Y. macrolepis, Y. parvus, Y. pleurotaenia, Y. polylepis, and Y. spanisbripes. However, the new spe- cies can be readily differentiated from these congeners by the following combination of characters: eye diameter shorter than interorbital width (vs. longer in Y. jiuchiensis and Y. Jongibulla), outer gill raker absent (vs. present in Y. macrolepis and Y. spanisbripes), processus dentiformis absent (vs. present in Y macrogaster, Y. parvus, and Y. pleurotaenia), six branched pelvic-fin rays (vs. seven or eight in ¥. chuanheensis), eight branched dorsal-fin rays (vs. nine in ¥. polylepis), and specific metric characters. Description. All morphometric and meristic data are given in Table 1. Greatest body depth anterior to dorsal fin origin, posterior portion gradually compressed from dorsal fin to caudal fin base. Lateral head longer than deep, deep- er than wide. Snout slightly blunt, shorter than postorbital length of head. Eye diameter smaller than interorbital width; posterior nostril closer to anterior margin of eye than to tip of snout; anterior and posterior nostrils separated by distance greater than diameter of posterior nostril; base of anterior nostril tube-shaped, not elongated to barbel-like structure. Zoosyst. Evol. 101 (2) 2025, 465-471 Table 1. Morphometric and meristic data of Yunnanilus triangulus sp. nov. Paratypes (mean + SD) Females (N = 5) 49.6-67.3 (55.6 + 7.0) 38.9-54.6 (44.1 + 6.1) 21.6-23.1 (22.1 + 0.6) 15.0-17.2 (15.7 + 0.9) 2/.1-29.0 (28.3 + 0.8) 51.3-55.4 (53.8 + 1.8) 99.8-99.9.(58..1 +: 1.5) 80.4-82.0 (81.4 + 0.7) 77.0-78.4 (77.5 + 0.6) 9.4-12.1 (10.7 + 1.0) 11.5-12.8 (12.1 + 0.5) 53/2-99.3(5915 22.5 59.1-60.9 (57.4 + 2.2 21.3-27.4 (24.0 + 2.2 31.7-38.1 (35.1 + 2.4 Males (N = 2) 47.8-49.3 (48.6 + 1.1) 37.1-39.1 (38.1 + 1.4) 20.9-21.2 (21.1 + 0.2) 14.3-14.4 (14.3 + 0.0) 29.9-30.9 (30.4 + 0.7) 53.6-54.8 (54.2 + 0.8) bor9—57.4 (57.3--0:5) 80.2-81.7 (80.9 + 1.1) 77,1-77.2 (77.1 + 0.1) 10.9-11.8 (11.3 + 0.6) 11.4-12.1 (11.8 + 0.5) 46.2-48.0 (47.1 + 1.2 49.6-56.9 (53.2 + 5.2 22.7-23.0 (22.8 + 0.2 31.2-35.2 (33.2 + 2.8 105.9-130.6 (113.1 + 10.2) ( ) ( ) ( ) ( ) 19.6-23.8 (21.0 + 1.6) 21.3-21.4 (21.4 + 0.0) ( ) ( ) ( ) ( ) 102.5-104.9 (103.7 + 1.7) 56.9-76.5 (66.9 + 8.0) 89.0-92.0 (90.5 + 2.1) 53.2-66.1 (61.5 + 5.5) 74.1-76.6 (75.4 + 1.8) Characters Holotype Total length (mm) 51.8 Standard length (mm) 40.8 Percent of standard length (%) Deepest body depth 20.4 Head width 15.5 Lateral head length 274 Predorsal length 54.9 Prepelvic length 55.8 Preanal length 78.7 Preanus length 7025 Caudal-peduncle length 130 Caudal-peduncle depth 22 Percent of Lateral head length (%) Head width 56.1 Head depth 60.0 Eye diameter 22.8 Interorbital width 23:9 Snout length 31.5 Percent of Caudal-peduncle length (%) Caudal-peduncle depth 94.0 Percent of distance between pectoral-fin origin and pelvic-fin origin Pectoral-fin length 73.8 Percent of distance between pelvic-fin origin and anal-fin origin Pelvic-fin length 69.1 Dorsalfin rays 3-6 Pectoral-fin rays 1, 10 Pelvic-fin rays 126 Analfin rays 2g Branched caudalfin rays 16 Body densely scaled, except head and thorax; scales more numerous and larger in males from pectoral to pel- vic-fin insertion. Three pairs of barbels, two rostral pairs and one maxillary pair, length of inner rostral barbel one half of outer rostral barbel, reaching anterior nostril; out- er rostral barbel reaching posterior nostril, and maxillary barbel reaching posterior margin of eye. Processus denti- formis on upper jaw absent. Dorsal fin with three unbranched and eight branched rays, origin closer to caudal-fin base than to snout tip, predorsal length 51.3-55.4% SL. Pectoral fin with one unbranched and 10-11 branched rays. Pelvic fin with one unbranched and six branched rays, origin posteri- or to dorsal fin origin, tips of adpressed fin not reaching anus, longer in males than females (74.1%—76.6% of dis- tance between pelvic-fin insertion and anal-fin origin vs. 53.2%—69.1% in females). Anal fin with two unbranched and five branched rays, origin closer to anus and distant from caudal fin. Caudal fin with two unbranched and 15- 17 branched rays (mostly 16). Series of temporal tubercles present on caudal peduncle in nuptial males. Lateral line incomplete, terminating between tip of pectoral fin and dorsal fin origin. 9-11 inner gill rakers on first gill arch. Cephalic lateral system with 12—15+3 infraorbital canal pores, 7-9 supraorbital canal pores, 6—8 supratemporal canal pores, and 6—10 preoperculomandibular canal pores. 3.6 3,8 1, 10-11 1, 10-11 hs: Ls vs) Zee 15-17 16 Stomach U-shaped (Fig. 2B); intestine long and straight. Swim bladder divided into two chambers; ante- rior chamber covered by dumbbell-shaped bony capsule, and posterior chamber well developed, connected to an- terior chamber by a slender tube, approximately half pos- terior chamber in length (Fig. 2A). Coloration. In life, head and trunk with light golden background color. Ventral head and abdomen surface without color pattern. In females, trunk with 15—17 long and twisted dark brown saddles, connected together on dorsal. Some bars bifurcated (Fig. 1H). In males, body with black longitudinal stripe on both sides (Fig. 1D). Fin rays with dark pigments, fin membrane hyaline. In for- malin-fixed specimens, lateral stripes and blotches some- what faded, body generally light yellow. Sexual dimorphism. Series of temporal tubercles present on caudal peduncle in nuptial male individuals (Fig. 2C), absent in females. Pelvic fin longer in males than females. Males without color patterns except for longitudinal stripes on body sides, females with long and twisted bars on trunks. Tubercles triangular, semi-translu- cent, angle to the body approximately 30 degrees, yellow- ish when preserved in formalin. Distribution and habitat. Yunnanilus triangulus sp. nov. is currently only known from Dalongtan Spring, Wangma Village, Huaning County, Yuxi City, Yunnan, China; Nanpan zse.pensoft.net 468 Liu, M. et al.: A new species of Yunnanilus Figure 1. Morphometric characters of Yunnanilus triangulus sp. nov. A—D. Lateral, dorsal, and ventral views, as well as a living photo of male, paratype KIZ2018002405; E—H. Lateral, dorsal, ventral, and living photo of female, holotype KIZ2018002410. Scale bar: 1 cm. A B anterior chamber stomach intestine posterior chamber Figure 2. Air bladder (A), stomach and intestine (B) (KIZ2018002404), and male tubercles on caudal peduncle (C) (KIZ2018002405) in Yunnanilus triangulus sp. nov. River (24.1716°N, 102.9182°E, 1619 m a.s.l.). The habitat comprises a deep pool, approximately 3 m in depth and characterized by abundant macrophytes (Fig. 3). Sympatric fish species at the time of collection included Discogobio yunnanensis, Pseudorasbora parva, and Carassius auratus. Genetic comparisons. In total, 1746 base pairs (670 bp for COI and 1 076 bp for Cyt 5) from Yunnani- lus triangulus sp. nov. were amplified and analyzed in zse.pensoft.net this study. These sequences were used for molecular phylogenetic analysis together with 37 complete mi- tochondrial genomes, 25 Cyt 6b sequences, and 21 COI sequences from GenBank. Parabotia fasciata Dabry de Thiersant, 1872, and Leptobotia elongata (Bleek- er, 1870), two botiid species, served as the outgroups. Given that the BI and ML analyses produced near- ly identical topologies, only the BI tree with BPPs and 469 Zoosyst. Evol. 101 (2) 2025, 465-471 A 98°0'E 9POE 100°0E 101°OCE 102°0E 103°0E 104°0E 105°0E 106°0E B 98°0'E 9P0E 100°0E 101°0E 102°0E 103°0E 104°0E 105°0E 106°0E Figure 3. Type locality of Yunnanilus triangulus sp. nov. A. Distribution map; B. Habitat photo of type locality at time of collection. bootstrap support (BS) values is presented (Fig. 4). The phylogenetic tree strongly supported the placement of Yunnanilus triangulus sp. nov. within Yunnanilus. The new species also formed a monophyly with Y. analis, Y. chuanheensis, and Y. pleurotaenia (BPP = 1; BS = 99) and exhibited a sister relationship to Y. jiuchiensis and Y. polylepis. However, the molecular phylogenies did not support the monophyly of Yunnanilus itself. In particular, Yunnanilus yangi was weakly supported as a sister group to Eonemachilus (BPP = 59; BS = 71), forming a clade with other species of Yunnanilus (Fig. 4). The uncorrected p-distances of the Cyt b and COI genes between Yunnanilus triangulus sp. nov. and the other six species ranged from 1.19% to 7.5% (average 3.13%). The maximum and minimum uncorrected p-distances were found between Y. yangi and Y. polylepis and between Y. analis and Y. pleurotaenia, respectively (Table 2). Discussion Molecular analysis unequivocally placed Yunnanilus tri- angulus sp. nov. within the genus Yunnanilus. This place- ment was further corroborated by several morphological features characteristic of the genus, including mouth in- ferior, lateral and cephalic lateral line pores present, an- terior and posterior nostrils separated, an anterior nostril tube-shaped, and a tip not elongated into a barbel-like structure (Du et al. 2023; Qin et al. 2024). The description of this new species increases the total number of Yunnanilus species native to the Yangtze, Pearl, and Red River basins to 21. Notably, Yunnanilus triangu- lus sp. nov. can be distinguished based on a combination of morphological characteristics related to the presence of scales, relative sizes of the eye diameter and interorbital width, absence of a processus dentiformis, lack of an out- er gill raker on the first gill arch, and the specific number of branched caudal fin rays. The genus Yunnanilus can be broadly divided into two morphological groups based on the presence or absence of body scales. The ‘scaleless’ group contains Y. analis, Y. beipanjiangensis, Y. chui, Y. dis- coloris, Y. forkicaudalis, Y. paludosus, and Y. yangi, while the ‘scaled’ group includes the new species together with Y. chuanheensis, Y. elakatis, Y. jiuchiensis, Y. longibulla, Y. macrogaster, Y. macrolepis, Y. macrositanus, Y. nanpanjian- gensis, Y. parvus, Y. pleurotaenia, Y. polylepis, Y. sichuan- ensis, and Y. spanisbripes. However, Yunnanilus triangulus Sp. nov. can be distinguished from Y. elakatis, Y. macros- itanus, Y. nanpanjiangensis, and Y. sichuanensis by whole body covered by scales, except head and thorax (vs. scales present only on caudal peduncle), from Y. /ongibulla and Y. Jiuchiensis by eye diameter shorter than interorbital width (vs. longer), from Y. parvus, Y. macrogaster, Y. pleurotae- nia, Y. macrolepis, Y. spanisbripes, and Y. longibulla by Table 2. Uncorrected p-distances (%) between nine species in the genus Eonemachilus and Yunnanilus based on mitochondrial COI and Cyt b genes. 1 2 3 1 2 E. longidorsalis 8.14 3. Yunnanilus yangi 9.64 12.08 4 Y. polylepis OeL7 10.64 9.44 5 Y. triangulus 8.53 9.79 7.54 6 Y. jiuchiensis 6.76 7.88 7.29 7 Y. chuanheensis 9.99 11.33 6.66 8 Y. pleurotaenia 8.55 10.20 7.42 9 Y. analis 6.89 7.82 7.46 Eonemachilus niger 4 5 6 7 8 4.34 3.88 1.89 5.89 2.43 247 4.18 1.19 1.86 2.03 4.35 1.37 2.26 Uaeyd 0.05 zse.pensoft.net 470 4/100 Parabotia fasciata KM393223 Leptobotia elongata JQ230103 4/100! 41/100 1/99) 1/100 1/100) 1/99 4/99 1/100 1/100 1/66 1/100 1/100 1/95) 1/100) 4/100} 0.05 0.99/98} Liu, M. et al.: A new species of Yunnanilus Petruichthys brevis NC031637 4/100, Homatula potanini KP749475 Homatula berezowskii MH125163 4/100 Traccatichthys pulcher ON116516 4/100) Traccatichthys pulcher KF765806 Traccatichthys zispi ON116518 Lefua costata NC029385 Lefua echigonia AB054126 Triplophysa sellaefer KY851112 Karstsinnectes parva ON116520 1/100 Oreonectes polystignus ON116514 1/100 Oreonectes platycephalus NC031579 1/100) Oreonectes luochengensis ON116495 Oreonectes guananensis ON116507 1/100, Micronemacheilus pulcherrimus 0Q024374 Micronemachellus cruciatus NC033960 1/1007 Guinemachilus pseudopulcherrimus 0Q024375 4/00) Guinemachilus pseudopulcherrimus 0Q024377 4/400; |Guinemachilus longibarbatus ON116508 1/100) Guinemachilus longibarbatus ON148334 4/99) Guinemachilus bailianensis NC061031 Guinemachilus bailianensis ON116504 Troglonectes retrodorsalis ON116511 Troglonectes longibarbatus MT361977 Troglonectes furcocaudalis NC032384 Paranemachilus jinxiensis NC039380 Paranemachilus genilepis MT845213 4/100) Paranemachilus pingguoensis MW043720 Paranemachilus zhengbaoshani ON116530 1/78 Paranemachilus chongzuo MW532082 Eonemachilus niger NC063106 Eonemachilus longidorsalis OM732331 4moor Yunnanilus yangi OP676117 Yunnanilus yangi OP676115 87/99" Yunnanilus yangi OP676114 Yunnanilus polylepis DLN20230184 Yunnanilus polylepis DLN20230183 Yunnanilus polylepis DLN20230182 Yunnanilus polylepis DLN20230181 4/100) 4/100 Yunnanilus polylepis DLN20230180 Yunnanilus jiuchiensis MW532080 Yunnanilus triangulus CB87 Yunnanilus triangulus CB86 Yunnanilus triangulus CB85 Yunnanilus triangulus CB84 Yunnanilus triangulus CB83 1/99 Yunnanilus chuanheensis MW574952 Yunnanilus pleurotaenia OQ024381 Yunnanilus pleurotaenia DLN20230201 Yunnanilus pleurotaenia DLN20230207 Yunnanilus pleurotaenia DLN20230203 1/96] | Yunnanilus pleurotaenia DLN20230199 Yunnanilus pleurotaenia DLN20230197 Yunnanilus pleurotaenia DLN20230196 199} Yunnanilus pleurotaenia DLN20230194 Yunnanilus pleurotaenia DLN20230193 Yunnanilus pleurotaenia DLN20230192 Yunnanilus pleurotaenia DLN20230206 Yunnanilus pleurotaenia DLN20230198 Yunnanilus pleurotaenia DLN20230195 Yunnanilus analis MW729320 Yunnanilus pleurotaenia DLN20230205 Yunnanilus pleurotaenia DLN20230191 Yunnanilus pleurotaenia DLN20230202 Yunnanilus pleurotaenia DLN20230200 1/100} Figure 4. Bayesian phylogram of Yunnanilus based on a concatenated dataset of mitochondrial cytochrome c oxidase subunit I (COI) and cytochrome b (Cyt 5) sequences. Numbers on branches represent BPPs from BI and bootstrap supports from ML. processus dentiformis absent (vs. present), from Y. macro- lepis and Y. spanisbripes by outer gill raker on first gill arch absent (vs. present), and from Y polylepis by body depth 20.0%—23.0% SL (vs. 15.0%-20.0%) and caudal peduncle depth 94.0%-131.0% of its length (vs. 73.0%-89.0%). Sexual dimorphism 1s a common characteristic in mem- bers of the family Nemacheilidae. For example, males of the genus Oreonectes develop genital papillae posterior to the anus (Du et al. 2008); those of the genera 7riploph- ysa and Barbatula exhibit thickened and widened outer branched pectoral-fin rays, accompanied by a slender pad of tubercles located anteroventral to the orbit (Zhu 1989). In Yunnanilus, sexual dimorphism is often expressed through color pattern variations. Although Qin et al. (2024) documented the presence of small tubercles on the body in nuptial males of Y. polylepis, with the presence of triangular tubercles on the caudal peduncle in nuptial males not previously reported. Zhang and Shen (1999) suggested that nuptial tubercles typically occur in areas of the body in contact during courtship or male-male com- petition, potentially serving to facilitate close physical in- teraction. Hence, we hypothesize that the caudal peduncle tubercles observed in Yunnanilus triangulus sp. nov. play a role in stimulating ovulation in females. However, fur- ther studies are necessary to validate this proposition. Species of Yunnanilus are typically confined to small water bodies rich in submerged macrophytes, environ- ments highly vulnerable to anthropogenic impacts and pollution. In September 2024, a survey of the type locality zse.pensoft.net of Yunnanilus triangulus sp. nov. revealed that the species had disappeared in the pond, likely due to the rapid de- cline of submerged macrophytes and the introduction of large numbers of carp into the habitat. The sensitivity of Yunnanilus to water pollution, invasive species, and pre- dation has led to consistent population declines across its range. These findings underscore the urgent need for targeted conservation strategies to safeguard Yunnani- /us species and other freshwater fish in this ecologically significant karst region. It 1s hoped that this report will stimulate further research and conservation initiatives to address the growing threats faced by freshwater ecosys- tems in southwestern China. Nomenclatural acts registration The electronic version of this article in portable doc- ument format represents a published work according to the International Commission on Zoological No- menclature (ICZN); hence the new name contained in the electronic version is effectively published under the Code from the electronic edition alone (see Arti- cles 8.5—8.6 of the Code). This published work and the nomenclatural acts it contains have been registered in ZooBank LSIDs (Life Science Identifiers) and can be resolved and the associated information can be viewed through any standard web browser by appending the LSID to the prefix http://zoobank.org/. Zoosyst. Evol. 101 (2) 2025, 465-471 Authors’ Contributions M.L. and L.-N.D. measured the specimens, analyzed the data, conceived and designed the study, and prepared the manuscript, J.-B.L. analyzed the molecular data and con- structed the phylogenetic tree. X.-Y.C. provided concep- tualization and funding acquisition for the field survey and resources. All authors read and approved the final version of the manuscript. Acknowledgments This study was funded by the Project of the Innovation Team of Survey and Assessment of the Pearl River Fish- ery Resources (2023TD-10), Guangxi Natural Science Foundation Project (2022GXNSFAA035563), Key Lab- oratory of Ecology of Rare and Endangered Species and Environmental Protection (Guangxi Normal University), Ministry of Education, China (ERESEP2022Z05), and the Position of Bioclassonomist of Chinese Academy of Sciences (CAS-TAX-24-054). We are grateful to L.L. Xu and H.D. Lyu for collecting specimens. We thank C. Watts for English corrections and suggestions. We thank C.Y. Lei for providing topotype specimens of Yunnanilus yan- gi. We especially thank help and supports from Bureau of Parks and Woods of Yuxi City throughout the field survey. 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