Xylochironomus Cranston newly recorded in the Oriental region (Diptera, Chironomidae), with description of three new species

127 Xylochironomus Cranston newly recorded in the Oriental region (Diptera, Chironomidae), with description of three new species Shutang Liu1, Hongqu Tang1 1 Research Centre of Hydrobiology, Jinan University, Guangzhou 510632, China Corresponding author: Hongqu Tang ([email protected]) Copyright: © Shutang Liu & Hongqu Tang. This is an open access article distributed under terms of the Creative Commons Attribution License (Attribution 4.0 International – CC BY 4.0). Research Article Abstract Three new species of Xylochironomus Cranston are described here based on adult males from the Oriental region, specifically from South China and East Malaysia. The generic diagnosis for the adult male is emended, and a key to the males of known species is provided. This is the first formal record of Xylochironomus from the Oriental region, and indeed the first occurrence outside the Australian region, providing another representative in the Gondwana biogeographic clade. Key words: Emendation, first record, key, new species, Oriental region, taxonomy Introduction Xylochironomus Cranston is a monotypic genus based on northern Australian material, with the type species Xylochironomus kakadu Cranston (Cranston 2006). As one of the typical wood-mining chironomids, the adult and larva which are subject to different evolutionary pressures, show two different morpho-responses and evolutionary pathways. The adult male resembles those Polypedilum (Pentapedilum), while the larva is clearly distinct, e.g., the orientation and shape of the ventromental lobe and mandible, which is associated with a mining immersed-wood life. Similar larvae were found subsequently in Thai streams (Sriariyanuwath et al. 2015), and they were noted in the South East Asia guide (Cranston and Tang 2024). However, no adult species has been reported to date in this region. During the diversity exploration in Southeast Asia and South China in recent years, several unusual species of subgenus “Pentapedilum” formed an independent clade when testing the molecular phylogeny using multi-gene makers, closely nested with the Australian Xylochironomus kakadu (voucher no.: AUNT04), and then the Endochironomus complex and Stenochironomus complex, rather than the presumed Polypedilum complex (personal unpublished data). Further examination of the morphological characters reveals that all belong to the genus Xylochironomus Cranston, and all are new to science. Here, we describe X. meng sp. nov., X. mulu sp. nov. and X. yue sp. nov., and provide some generic emendations. Academic editor: Viktor Baranov Received: 26 June 2025 Accepted: 6 October 2025 Published: 29 October 2025 ZooBank: https://zoobank. org/3476CC85-DFAF-47FE-818E05AA26B19E54 Citation: Liu S, Tang H (2025) Xylochironomus Cranston newly recorded in the Oriental region (Diptera, Chironomidae), with description of three new species. ZooKeys 1257: 127–135. https://doi. org/10.3897/zookeys.1257.163285 ZooKeys 1257: 127–135 (2025) DOI: 10.3897/zookeys.1257.163285 128 ZooKeys 1257: 127–135 (2025), DOI: 10.3897/zookeys.1257.163285 Shutang Liu & Hongqu Tang: Three new species of Xylochironomus Cranston in the Oriental region Material and methods Adults were collected using light traps or sweeping nets. All specimens were slide-mounted in Euparal. Photographs were taken of each specimen under an Olympus BX53 compound microscope using a mounted camera (ToupViewTM). Digital photographs of different focal planes were stacked using Helicon Focus version 7. Line drawings were aided by the use of a drawing tube attached to an Olympus BX53. Morphological terminology and abbreviations largely follow Sæther (1980). Measurements are given as ranges, with the number of observed specimens in parentheses if different from the number (N) stated at the beginning of the description. All material is deposited in the Department of Ecology, Research Centre of Hydrobiology, Jinan University, Guangzhou, Guangdong. Genus Xylochironomus Cranston, 2006 Type species. Xylochironomus kakadu Cranston, 2006. Diagnosis. The specimens examined conform in most diagnostic features to the generic description of the adult male (Cranston 2006). Based on the material described below, the generic diagnosis for Xylochironomus should be emended as follows. Adult male. Frontal tubercles small, reduced. Acrostichals biserial, starting from the anterior scutum. Parapsidal suture thick (Fig. 2A). Scutal hump with a weak hump, very low. Wing cuneiform and setose, anal lobe clearly reduced, apex of wing somewhat rectangular, with an interrupted costal extension (Fig. 1A–C). Squama bare or with fewer than 3 setae. Mid and hind tibiae with 2 separated combs, only the outer comb with a long-curved spur, the length ratio of ta4/ta5 in the fore and hind leg usually no less than 2.0. Segment VIII tapered anteriorly (Fig. 1D) or indistinct in some teneral form. Insertion of lateral seta of superior volsella arising basal-dorsally or from basal margin; outer seta usually much longer than the length of the superior volsella. Inner margin setae of gonostylus short and sparse, unequal-distance or irregular. Anal tergite band separated, anal median seta tends to be uniserial if less than 6 setae, no tendency to be enclosed by a round and sclerotized anal tergite circle. Adult female, pupa and larva. See Cranston (2006). Xylochironomus meng sp. nov. https://zoobank.org/B89E5217-9295-4FB4-BA2B-C24CC521E20B Figs 1A, 1E, 2A, B Material examined. Holotype: M, China • Yunnan Province, Pu’er City, Ximeng Wa Autonomous County, Longtan Pool in Mengsuo Town, 22°38'N, 99°35'E, alt. 1,917 m, light traps, 27.viii.2014, HQ Tang. Paratype: • 1M, same as holotype except 26.iv.2022. Diagnosis. The new species is characterised by the gonostylus with an acute apex and high leg value (LR1 2.2–2.4). Etymology. For the type locality, “meng” is a term used to refer to certain places in Yunnan dialect, similar to a town or county. The name is a noun in apposition. 129 ZooKeys 1257: 127–135 (2025), DOI: 10.3897/zookeys.1257.163285 Shutang Liu & Hongqu Tang: Three new species of Xylochironomus Cranston in the Oriental region Figure 1. Color photos of wing apex (A–C, arrows indicate the costa disjunction), abdominal terminal (D, arrow indicates the constricted anterior TVIII) and male genitalia (E–G). A, E. X. meng sp. nov.; B, D, F. X. mulu sp. nov.; C, G. X. yue sp. nov. Scale bars: 200 µm (A–C); 100 µm (D–G). 130 ZooKeys 1257: 127–135 (2025), DOI: 10.3897/zookeys.1257.163285 Shutang Liu & Hongqu Tang: Three new species of Xylochironomus Cranston in the Oriental region Description. Male imago (N = 2). Total length 2.8–3.3 mm. Wing length 1.6–1.7 mm. Total length/Wing length 1.71–1.97. Head. Antennal terminal flagellomere 460–490 μm long, AR 0.72–0.80; apex with 2–3 long terminal setae, 85–110 μm long. Frontal tubercle ca. 2–3 μm long. Temporals with 4–6 verticals. Clypeus with 15–21 setae. Palpomeres 1–5 (in μm): 25–30; 50–55; 110–130; 110–125; 200–240 in length. Thorax. Acrostichals 10–12; dorsocentrals 8–10; prealars 3–4; scutellars 8–10. Wing. VR 1.16–1.21. R with 45–55 setae; R1 with more than 50 setae; R4+5 with more than 150 setae. Square 2–3 setae. Legs. Scale of fore tibia round, 25–35 μm long, spurs of mid tibia and hind tibia 35–55 μm and 50–65 μm long, respectively. Lengths and proportions of legs as Table 1. Hypopygium (Figs 1E, 2B). Tergite IX with 5–8 median setae, arranged in one or two rows. Anal point parallel, 45–48 μm long, not reaching the apex of inferior volsella. Gonocoxite 150–165 μm long, superior volsella 40–50 μm long, with two basal inner setae and one additional (‘outer’) seta, arising from the basal margin of superior volsella, 75–80 μm long, extending near the apex of inferior volsella. Gonostylus 120–125 μm long, with acute apex. HR 1.28–1.38. Remarks. The new species somewhat resembles the Okinawa species Polypedilum (Pentapedilum) acristylum Yamamoto, Hirowatari & Yamamoto, 2012 (Yamamoto et al. 2012). Both have an acute apex to the gonostylus, and the location of the outer seta of the superior volsella is more basal. However, in P. acristylum, the outer seta of the superior volsella is relatively short, not extending beyond the apex of the superior volsella, the squama has 9 setae, and the ratio of ta4/ta5 in the middle leg is 1.5, and thus P. acristylum is not a member of Xylochironomus, but an atypical species of Polypedilum (Pentapedilum). Xylochironomus mulu sp. nov. https://zoobank.org/52682106-1548-4F4D-A02E-286B2DBA8071 Figs 1B, 1F, 2C Material examined. Holotype: M, Malaysia • Sarawak, Gunung Mulu National Park, Melinau stream, Paku tributary, alt. 75 m, 04°1'N, 114°49'E, light traps, 12.vi.2023, leg. H.Q. Tang. Paratype: • 1M as holotype. Diagnosis. The new species is characterised by the presence of a small frontal tubercle and the contour of the superior volsella. Etymology. From the type locality, Gunung Mulu National Park. The name is a noun in apposition. Table 1. Lengths (in µm) and proportions of leg segments of Xylochironomus meng sp. nov., male (N = 2). fe ti ta1 ta2 ta3 ta4 ta5 LR P1 850–1000 430–550 1120–1225 775–800 500–510 425–440 170–180 2.23–2.40 P2 820–985 680–825 430–500 250–290 170–210 110–140 60–70 0.59–0.63 P3 870–1000 720–828 570–700 320–375 290–350 190–225 80–100 0.79–0.85 131 ZooKeys 1257: 127–135 (2025), DOI: 10.3897/zookeys.1257.163285 Shutang Liu & Hongqu Tang: Three new species of Xylochironomus Cranston in the Oriental region Description. Male imago (N = 2). Total length 2.8–3.2 mm. Wing length 1.4–1.5 mm. Total length/Wing length 1.93–2.19. Figure 2. Color photos of Xylochironomus thorax (A) and line drawings of genitalia (B–D). A, B. X. meng sp. nov., arrow indicates the thick parapsidal suture; C. X. mulu sp. nov.; D. X. yue sp. nov. Scale bars: 100 µm (A); 50 µm (B–D). 132 ZooKeys 1257: 127–135 (2025), DOI: 10.3897/zookeys.1257.163285 Shutang Liu & Hongqu Tang: Three new species of Xylochironomus Cranston in the Oriental region Head. Frontal tubercle small, 5–6 μm wide and 6–10 μm long. Antenna terminal flagellomere 420–450 μm long, apex with 2–3 long apical setae, 80–100 μm long. AR 0.79–0.84. Temporals with 8–12 inner verticals. Clypeus with 18–21 setae. Lengths of palpomeres 1–5 (in μm): 30–33; 45–50; 100–110; 120–125; 190–210. Thorax. Acrostichals 16–20; dorsocentrals 8–9; prealars 3; scutellars 5–7 biserial setae, anterior row with 2–4 small setae medially. Wing. VR 1.18–1.20. R, R1 and R4+5 with more than 35 setae. Squama with 0–2 setae. Legs. Scale of fore tibia tongue-shaped, 25–30 μm long; spurs of mid tibia and hind tibia 60–70 and 55–70 μm long, respectively. Lengths and proportions of legs as Table 2. Hypopygium (Figs 1F, 2C). Tergite IX with 4–6 median setae in one row. Anal point 50–55 μm long, extending to the subapex of inferior volsella. Gonocoxite 150–155 μm long, superior volsella with two basal inner setae arising from the distinct tubercles, and one outer seta, arising from the basidorsal surface of superior volsella, 70–80 μm long, extending the apex of inferior volsella. Gonostylus 115–120 μm long. HR 1.25–1.30. Remarks. The new species is characterized by the relative location between inner and outer seta of the superior volsella, and the outer seta extending beyond the terminals of the inferior volsella. The shape of the gonostylus seems to vary depending on orientation. Xylochironomus yue sp. nov. https://zoobank.org/FC5A8FAA-572B-40D0-B29A-3AB068971961 Figs 1C, 1G, 2D Material examined. Holotype: M, China • Guangdong Province, Guangzhou City, Conghua District, Lyutian Town, Fentian, 23°50'N, 113°56'E, alt. 260 m, light traps, 02.iv.2018, leg. HQ Tang. Paratype: • 1M, as holotype. Diagnosis. The new species can be separated from congeners by the large wing length (c. 2.0 mm), wing squama with 1–3 setae, and the outer seta of the superior volsellae distinctly extending beyond the apex of the superior volsellae. Etymology. For the type locality, “yue” is an abbreviation of Guangdong Province. The name is a noun in apposition. Description. Male imago (N = 4). Total length 3.0–3.2 mm. Wing length 1.8–1.9 mm. Total length/Wing length 1.68–1.75. Table 2. Lengths (in µm) and proportions of leg segments of Xylochironomus mulu sp. nov., male (N = 2). fe ti ta1 ta2 ta3 ta4 ta5 LR P1 1000–1050 510–540 n/a n/a n/a n/a n/a n/a P2 900–1050 750–825 625–670 325–360 300–330 200–220 100–110 0.81–0.83 P3 870–880 720–800 440–490 250–270 180–190 110–140 60–70 0.61–0.62 133 ZooKeys 1257: 127–135 (2025), DOI: 10.3897/zookeys.1257.163285 Shutang Liu & Hongqu Tang: Three new species of Xylochironomus Cranston in the Oriental region Head. Frontal tubercle present, ca. 5 μm long. Antenna terminal flagellomere 510 μm (N = 1) long. AR 0.80 (N = 1). Temporals with 10–12 inner verticals. Clypeus with 18–21 setae. Lengths of palpomeres 1–5 (in μm): 30–35; 40–45; 120–125; 125–130; 235–240. Thorax (N = 1). Acrostichals 14; dorsocentrals 8; prealars 3; scutellars 9, uniserial. Wing. VR 1.18–1.20. R, R1 and R4+5 with more than 40 setae. Squama with 1–3 setae. Legs. Scale of fore tibia 30 μm long; spurs of mid tibia and hind tibia 35– 45 μm and 50–60 μm long, respectively. Lengths and proportions of legs as Table 3. Hypopygium (Figs 1G, 2D). Tergite IX with 6–10 median setae, arranged in one row, and 4–6 margin setae on each side. Posterior margin of TIX somewhat smooth. Anal point parallel, 60 μm long, extending not beyond the inferior volsella. Gonocoxite 150–155 μm long, superior volsella 55–60 μm long, with three basal inner setae and one outer seta 80–85 μm long, extending to the apex of inferior volsella slightly. Gonostylus 120–130 μm long, with attenuated apex. HR 1.20–1.25. Remarks. This new species resembles Xylochironomus kakadu Cranston in the shape of the posterior margin of TIX and superior volsella, while the outer seta of the superior volsella is different, clearly extending beyond the terminal of the superior volsella in this new species, but relatively shorter in the latter, less than the whole length of the superior volsella. Key to all known species of adult males of Xylochironomus Cranston, 2006 1 Wing membrane strongly hirsute, with some stable macrotrichiae (Fig. 1C); length of superior volsella subequal or slightly shorter than the anal point ...............................................................X. yue sp. nov. (China, Guangdong) – Wing membrane microtrichiose, only some setal pits remain (Fig. 1A, B); length of superior volsella clearly shorter than the anal point ...................2 2 Posterior margin of TIX somewhat smooth or truncated. Wing squama bare. Foreleg ratio more than 2.5 .......... X. kakadu Cranston (N. Australia) – Posterior margin of TIX triangular. Wing squama usually with 1–3 setae. Foreleg ratio less than 2.5 ............................................................................3 3 Outer seta of superior volsella arising from the inner basal margin (Fig. 2B); gonostylus with an acute apex .......X. meng sp. nov. (China, Yunnan) – Outer seta arising from basal section of superior volsella (Fig. 2C); gonostylus with an attenuated apex ...........X. mulu sp. nov. (Malaysia, Sarawak) Table 3. Lengths (in µm) and proportions of leg segments of Xylochironomus yue sp. nov., male (N = 2). fe ti ta1 ta2 ta3 ta4 ta5 LR P1 1020–1030 540–560 1300 800 540 450 180 2.32 P2 1000–1060 800–880 510–540 280–290 200–210 120–130 60–70 0.61–0.64 P3 1025–1050 850–900 720–730 390–400 340–350 220–230 95–100 0.80–0.86 134 ZooKeys 1257: 127–135 (2025), DOI: 10.3897/zookeys.1257.163285 Shutang Liu & Hongqu Tang: Three new species of Xylochironomus Cranston in the Oriental region Discussion Generally, Xylochironomus Cranston can be separated from other similar genera by the reduced frontal tubercle and weak scutal hump, a few squama setae in the wing with somewhat rectangular apex and the peculiar location of the outer seta of the superior volsellae. Although the characters used in the generic diagnosis and key are summarized from limited slides, they are sufficient to separate the present species; however, there is no guarantee of reliability when further species are reported in the future. The most distinct generic characters come from those pupa and larva, such as the broken hook row on pupal tergite II, and the inclined larval ventromental plate. Hence, the associated material is most important when no molecular data is available. The new findings of male Xylochironomus from Eastern Malaysia and South China, together with the larval report from Thailand (Sriariyanuwath et al. 2015), is an example of another Gondwanan clade in the Oriental region, which has already been reported in Conochironomus Freeman, 1961 (Cranston 2016), Skusella Freeman, 1961 (Cranston and Tang 2018), Paraskusella Cranston, 2018 and Kribiodosis Kieffer, 1921 (Cranston 2018; Han et al. 2021; Tang and Cranston 2025). This distribution pattern is discussed as the tropical Gondwana track by Cranston (2005). More representatives, including their immature stages and molecular phylogenetic studies, will be necessary to further explore this pattern. Acknowledgements We are grateful to Dr Wu Han and Ms Tsz-Ying Chan (both from The University of Hong Kong) for their help with fieldwork in Sarawak. The specimens collected from Gunung Mulu National Park are under the research permit (SFC.810-4/6/1 (2023) –106) issued by Sarawak Forestry Corporation. The work was partially supported by the Special Fund for Basic Investigation Research of the Ministry of Science and Technology, China (2022FY100504). Additional information Conflict of interest The authors have declared that no competing interests exist. Ethical statement No ethical statement was reported. Use of AI No use of AI was reported. Funding No funding was reported. Author contributions Hongqu Tang: Conceptualization; data curation; supervision; writing –reviewand editing. Shutang Liu: Data curation; Line-drawings; investigation. 135 ZooKeys 1257: 127–135 (2025), DOI: 10.3897/zookeys.1257.163285 Shutang Liu & Hongqu Tang: Three new species of Xylochironomus Cranston in the Oriental region Author ORCIDs Shutang Liu https://orcid.org/0009-0008-7283-4932 Hongqu Tang https://orcid.org/0000-0002-4957-4617 Data availability All of the data that support the findings of this study are available in the main text. References Cranston PS (2005) Biogeographic patterns in the evolution of Diptera. In: Wiegmann BM, Yeates DK (Eds) The Evolutionary Biology of Flies. Columbia University Press, New York, 274–311. Cranston PS (2006) A new genus and species of Chironominae (Diptera: Chironomidae) with wood-mining larvae. Australian Journal of Entomology 45(3): 227–234. https:// doi.org/10.1111/j.1440-6055.2006.00539.x Cranston PS (2016) Conochironomus (Diptera: Chironomidae) in Asia: new and redescribed species and vouchering issues. 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