Xenochironomus rutundus, Mukherjee & Ghosh & Ray & Naskar & Banerjee, 2025

Mukherjee, Bindarika, Ghosh, Debjani, Ray, Namrata, Naskar, Atanu & Banerjee, Dhriti, 2025, A new species of the genus Xenochironomus Kieffer, 1921 (Diptera: Chironomidae) from India, with a tentative morphological cladistics and world checklist, Zootaxa 5716 (4), pp. 558-570 : 561-564

Genus Xenochironomus Kieffer, 1921

Species Xenochironomus rutundus sp. nov.

GenBank Accession No. PP620153.1

Material examined. Holotype male, India, West Bengal, Barddhaman , [ 23.2441°N 87.8368°E], 1.iii.2024, coll. B. Mukherjee. Paratype 1 male, labelled ‘ Xenochironomus rutundus sp. nov., India, West Bengal, Birbhum , 23.45°N 87.50°E, 6.iii.2024, coll. S. Mondal.

Diagnosis. The adult male is distinguished from other species of the genus Xenochironomus by the presence of a spherical-shaped superior volsella and leaf-like lateral stalk on the superior volsella.

Description of male (n = 2): Total length 3–3.5, 3.25 mm. Wing length 1.85–2, 1.92 mm. Costal length 1.65– 1.95, 1.85 mm. Antennal length 1.12–1.15, 1.135 mm. Head width 650–700, 675 µm.

Colouration. Thorax yellowish brown, wings clear, legs light brown, abdomen light brown.

Head. Temporal setae 10 (IV 4, OV 2, Po 4). Clypeal setae 17–18. Frontal tubercles absent. Eyes bare, with dorsomedial extension of 240–250, 245 µm. Ultimate flagellomere 775–780, 777.50 µm long; AR 2.20–2.50, 2.35. Length of palpomeres (I–V) (µm): 45: 50: 150: 150–160: 220–230. CA 0.58–0.61, 0.59.

Thorax. Acs 10, Dcs 7–9, Pa 2, Su 1, and Scts 3–4.

Wing ( Fig. 1A ). VR 1.05–1.15, 1.10. R with 14 setae, R1 with 6 setae, R 4+5 bare. Brachiolum with 2 setae. Squama with 10–11 fringed setae. FCu slightly distal to RM. Anal lobe well developed.

Legs. Fore tibia with 3 setae at apex. Mid legs with 2 unequal tibial spurs; 50 µm and 25–30 µm long, comb with 37–40 teeth. Hind leg with 2 unequal tibial spurs; 40 µm and 25 µm long, comb with 50–44 teeth. Lengths (µm) and proportions of legs are shown in Table 1.

Hypopygium ( Fig. 1C ; Figs. 2A–B ). Anal tergite band separated. Tergite IX with 4 median anal tergite setae. Anal point very broad, ventrally inverted, and a median ridge with 6–7 setae alongside. Transverse sternapodeme 50–55, 52.50 µm long; longitudinal sternapodeme 87.50–90, 88.75 µm long. Superior volsella ( Fig. 1C ) pubescent, complete globular shaped throughout, microtrichiose and with many short setae, 57.50–60, 58.75 long and 50 µm wide; a lateral leaf-like microtrichiose and setose stalk present on superior volsella, 30 long and 10 µm wide medially. Inferior volsella 130 µm long, cylindrical shaped, and branched setae at apex ( Fig. 2B ). Gonocoxite 120– 125, 122.5 µm long. Gonostylus 170–175, 172.50 µm long, parallel-shaped with a pointed apex. HR 0.71–0.72; HV 2.50–2.80, 2.65 ( Figs. 1B , 2A and B ).

Female and immature. Unknown.

Etymology. The name ‘ rutundus’, a Latin word, refers to the spherical-shaped superior volsella.

Distribution. India, West Bengal (present record).

Remarks. The presence of the median anal tergite setae, the broad and ventrally inverted anal tip, and the superior volsella with small setae covering the entire surface places this species in the genus Xenochironomus . The superior volsella of the new species resembles that of Xenochironomus xenolabis (Kieffer, 1916) in that it has a comparable shape but differs in the presence of a lateral hinge on the superior volsella and the shape of the anal point. Both the new species and X. lacertus Dutta & Chaudhuri, 1995 , the other species known from India, have pubescent superior volsellae and setae on the anal point; however, the new species is distinct from the latter in the shape of the inferior volsella, gonostylus, and the presence of a laterally hinged superior volsella. The new species has unique diagnostic characters, which we contrasted with existing Oriental species in Table 2.

Figures

FIGURE 1. Xenochironomus rutundus sp. nov. adult male, holotype (A–C). A. wing. B. hypopygium. C. superior volsella. (Scale 0.01 mm).

FIGURE 2. Xenochironomus rutundus sp. nov. adult male, holotype (A–B). A. hypopygium (dorsal view). B. branched setae of the inferior volsella. (Scale 0.01 mm).