Stictochironomus longtanensis Lei & Zhang sp. nov.
Figs 1, 2, 3
Type material.
Holotype: • ♂ (BOLD ID: HHC 011-25; Field ID: Chironomidae Stictochironomus S 1), permanently deposited in XYFU (catalogue number: XYFU -HHC 011); China, Henan Province, Xinyang City, Shihe District, Longtan Village, 31.9343 ° N, 113.9264 ° E, 4. IV. 2025, leg. Q. Lei, sweep net. Paratypes: • 2 ♂♂ (BOLD IDs: HHC 012-25, HHC 016-25), • 2 ♀♀ (BOLD ID: HHC 013-25, HHC 014-25), same data as holotype, same depository (catalogue numbers: XYFU -HHC 012, XYFU -HHC 013, XYFU -HHC 014, XYFU -HHC 016)
GenBank accession numbers.
PV 929838 – PV 929841.
Etymology.
The specific epithet is derived from the name of type locality, Longtan village.
Diagnostic characteristics.
Adult males of this new species can be distinguished from other known Stictochironomus by the following combination of morphological characters: hypopygium ratio large (1.98–2.11; mean: 2.06) and hypopygium value large (3.77–4.01; mean: 3.91); abdomen and hypopygium brown; white ring present on each side of femur; wing with a dark spot near cross vein r-m; superior volsella with six basal setae. Adult females can be distinguished from other known Stictochironomus species by the following combination of characters: antennal ratio small (AR 0.37–0.39); wing with a dark spot near cross vein r-m; genitalia with two ovoid, transparent seminal capsules; and cercus large, elliptical, and densely setose.
Description.
Adult male (n = 3) (Table 2). Total length 6.77–7.46 mm, mean: 7.20 mm. Wing length 3.55–3.87 mm, mean: 3.77 mm. Total length / wing length 1.90–1.91 mm, mean: 1.91 mm. Wing length / length of profemur 2.22–2.45, mean: 2.36.
Colouration. Head yellow and thorax brown. Legs distinctly annulated, with one white ring on femur and two white rings on tibia. On fore and mid legs (P 1, P 2), tarsomere I pale yellow at base and brown at apex, and tarsomeres II – V uniformly brown.
Head. AR 2.56–2.60, mean: 2.58. Temporal setae 15–19, mean: 18, including 4–5 (mean: 5) inner verticals; 5–8 (mean: 7) outer verticals; 6 postorbitals. Clypeus with 21–26 (mean: 24) setae. Tentorium 219–226 μm (mean: 223 μm) long, 69–94 μm (mean: 82 μm) wide. Palpomere lengths (in μm): 52–58 (mean: 55); 97–105 (mean: 101); 183–195 (mean: 189); 223–233 (mean: 228); 261–322 (mean: 292).
Thorax. Acrostichals 14–18 (mean: 16); dorsocentrals 12–14 (mean: 13); scutellars 27–28 (mean: 28); and prealars 7–9 (mean: 8).
Wing (Fig. 1 A). VR 0.93–0.97 (mean: 0.95). R with 24–27 (mean: 26); R 1 with 17–19 (mean: 18); R 4 + 5 with 22–24 (mean: 23) setae. Squama with 13–14 (mean: 14) setae.
Legs (Fig. 2 A). Tibial spur of mid leg 30–37 μm (mean: 34 μm) long; two tibial combs of mid leg 37–46 μm (41 μm) and 35–63 (46 μm) long, respectively. Tibial spur of hind leg 36–43 (mean: 40 μm) long; two tibial combs of hind leg 34–52 μm (mean: 40 μm) and 35–62 μm (mean: 49 μm) long, respectively. Tibial widths: fore leg, 68–76 μm (mean: 71 μm); mid leg, 82–94 μm (mean: 88 μm); hind leg, 86–105 μm (mean: 93 μm).
Hypopygium (Fig. 1 B, C). Tergite IX with 7–9 (mean: 8) setae. Laterosternite IX with 8–11 (9) setae. Anal point slender, 108–135 μm (mean: 119 μm) long, with parallel lateral margins at the distal end and 8–13 (10) basal setae. Phallapodeme 91–94 (mean: 92 μm) long. Transverse stermapodeme 63–71 (mean: 66 μm) long. Superior volsella 106–114 μm (111 μm) long, with 6 basal setae and a long seta on distal 1 / 3. Inferior volsella 187–192 μm (mean: 189 μm) long with 11–15 (13) setae on distal end. Gonocoxite 335–418 μm (mean: 380 μm) long and 90–143 μm (112 μm) wide. Gonostylus stout, 169–198 μm (mean: 184 μm) long and 44–84 μm (62 μm) wide. HR 1.98–2.11 (mean: 2.06). HV 3.77–4.01 (mean: 3.91).
Female (n = 2) (Table 3). Total length 6.57–7.03 mm. Wing length 3.52–3.79 mm. Total length / wing length 1.85–1.87. Wing length / length of profemur 2.31–2.53.
Colouration. Head yellow; thorax brown; abdomen and hypopygium yellowish brown. Femur with one white ring; tibia with two white rings. Tarsomere I basally pale yellow, apically brown; tarsomeres II – V uniformly brown.
Head. AR 0.37–0.39. Temporal setae 16–20 including 4–6 inner verticals; 7–8 outer verticals; 5–6 postorbitals. Clypeus with 24–28 setae. Tentorium 206–207 μm long, 74–97 μm wide. Palpomere lengths (μm): 60-68; 97–107; 165–178; 222–227; 319–334.
Wing (Fig. 3 A). VR 0.90–0.96. R with 30–37, R 1 with 24–34, R 4 + 5 with 51–56 setae. Squama with 15–21 setae.
Thorax (Fig. 3 B). Acrostichals 18–21, dorsocentrals 19, Scutellars 26–32, and prealars 6–8.
Legs (Fig. 2 B). Tibial spur of mid leg 36–41 μm long; two tibial combs 22–27 μm and 27–28 μm long, respectively. Tibial spur of hind leg 37–39 μm long; tibial combs of hind leg 29–31 μm and 34–39 μm long, respectively. Tibial widths: fore leg, 87–94 μm, mid leg, 102–116 μm, and the hind leg, 120–123 μm.
Genitalia (Fig. 3 C). Endophallus 228–237 μm long; basal inner process of ninth sternite 107–112 μm long. Notum 178–183 μm long. Cercus large, elliptical, densely setose, 229–243 μm long, 145–164 μm wide. Two seminal capsule vesicles, ovoid, and transparent.
Remarks.
The new species resembles S. sticticus and S. akizukii from China by sharing several characteristics, including the presence of rings on both the femur and tibia, a slender, elongated anal point with parallel lateral margins, and a hook-shaped superior volsella bearing a long seta at its proximal end. Stictochironomus sticticus may lack wing spots in some populations, although the specimens examined by Qi et al. (2008) possess a distinct dark spot near cross vein r-m. The inferior volsella is finger-like. Distinguishing features include that larger body size (6.77–7.46 mm in males and 6.57–7.03 mm in females) and a larger AR (2.56–2.60 in males and 0.37–0.39 in females). Notably, the hypopygium ratio (1.98–2.11, 2.06) and hypopygium value (3.77–4.01, 3.91) in male adults are greater. The female genitalia are characterized by having two ovoid, transparent seminal capsules and a large, elliptical, densely setose cercus measuring 229–243 μm long and 145–164 μm wide.
Distribution.
Currently, the new species is known from Henan and Zhejiang, China.
Analysis of DNA barcodes.
DNA barcoding successfully linked the morphologically distinct adult males and females of Stictochironomus longtanensis sp. nov. (Fig. 4). Pairwise genetic distance analyses (Table 4) revealed low intraspecific divergence, with a 0.00 % genetic distance observed among three specimens (PV 929840, PV 929841, and PV 929838) and only a 1.39 % difference in the fourth specimen (PV 929839). The average intraspecific genetic distance for S. longtanensis in this study was 0.69 %, which falls within the typical range reported for conspecific individuals in the Chironomidae family.
The neighbour-joining (NJ) tree placed S. longtanensis in a clade with S. sticticus from Japan and S. sinsauensis from South Korea (Fig. 4). The average interspecific genetic distances between S. longtanensis and these congeners were 12.4 % and 11.9 %, respectively. Notably, these values substantially exceed the maximum intraspecific divergence threshold (4.5–7.7 %) established for the genus Stictochironomus (Song et al. 2024), indicating the presence of a clear barcode gap. The minimum genetic distance from S. longtanensis to any recognized congener (11.40 %) further supports its taxonomic distinctness (Suppl. material 1). Collectively, phylogenetic and genetic evidence strongly support the recognition of S. longtanensis as a new species.
An updated key to the known males of Stictochironomus from China
This key is primarily based on Song et al. (2024).
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