Sympotthastia annularis Fu, 2025

Fang, Xiangliang, Shangguan, Jingru & Fu, Yue, 2025, Sympotthastia annularis sp. nov. from Oriental China (Diptera: Chironomidae: Diamesinae) with a worldwide key, Zootaxa 5717 (4), pp. 571-578 : 573-574

Sympotthastia annularis Fu , sp. nov.

Figure 1A–G , Figure 2A–F

Type material. Holotype male ( HNU: zdbs338): CHINA; Hubei Province, Huanggang City, Yingshan County, Dabie Mountain , Guatian waterfall; light trap; 31.1047°N 115.7913°E; 932 m a. s. l.; 5.IV.2023; collected by Zigang Xu. Paratype: 1 male ( HNU: zdbs33802), same as holotype .

Etymology. This new species is named after the Latin word “ annularis ”, meaning “ring-like” or “circular”, referring to the circular form created by the paired aedeagal lobe and superior volsella.

Diagnostic characters. This species can be distinguished from related species by a combination of the following characters: AR 3.71; anal point absent; aedeagal lobe and superior volsella fused into a ring-like structure (AL + SVo); median aedeagal lobe rounded; phallapodeme well developed with distinctly enlarged, shoe-shaped apex.

Description. Adult male ( N = 2)

Total length 5.13 –5.26 mm, Wing length 3.43–3.52 mm, TL/WL 1.49–1.50, WL/Pfe 2.19–2.25.

Coloration ( Fig. 1A ). Head, thorax, and tergites uniformly brown, except for some yellow areas in the middle part of the lateral sides of the thorax.

Head ( Fig. 1B ). Antenna with 13 flagellomeres; antennal ratio (AR) 3.71–3.74. The ultimate flagellomere tapers subapically, ends in a clavate (club-shaped) and medially concave apex, and possesses a single apical seta ( Fig. 1C ). Eyes bare, extending to the mid-dorsal region. Temporal setae total 10, comprising 3–4 outer verticals and 7–8 postorbitals; inner verticals absent. Tentorium 252–255 µm long, 61–63 µm wide. Stipes 249–253 µm long, 12–14 µm wide. Clypeus with 3–5 setae. Lengths of palpomeres 1–5 (in µm): 58–60, 87–88, 207–210, 334–336, 233–240. Length ratio of palpomere 5 to palpomere 3 (P₅/P₃) 1.13–1.14. Apex of palpomere 3 with a sclerotized projection ( Fig. 1D ).

Thorax ( Fig. 1E ). Antepronotal lobe with 10–12 basolateral setae; acrostichals absent, dorsocentrals 16–18; prealars 13–15; scutellars 69–70.

Wing ( Fig. 1F ). Anal lobes well developed. VR(Cu/M): 0.96; brachiolum with 8–10 setae; R with 9–10 setae; R 1 with 13–14 setae. Costal extension 69–70 µm.

Legs. The width of the fore tibia at its apex is 73–76 µm. The fore tibial spur 255–258 µm long; tarsomere I (ta₁) and tarsomere II (ta₂) each with 2 pseudospurs. The width of the mid tibia at its apex is 80–82 µm, spurs of mid tibia 68–70 µm and 76–78 µm long; tarsomere I (ta₁) with 7–8 pseudospurs, tarsomere II (ta₂) with 1 pseudospur. The width of the hind tibia at its apex is 72–75 µm, spurs 98–100 µm and 96–98 µm long; tarsomere I (ta₁) with 13–15 pseudospurs. Hind tibial comb composed of 18–20 spines, with the longest measuring 74–76 µm long and the shortest 39–41 µm long ( Fig. 1G ). The lengths and proportions of each leg are shown in Table 1.

Hypopygium ( Fig. 2A–F ). Tergite IX with 26–28 median setae and 8–10 setae on laterosternite IX. Anal point absent ( Fig. 2B ). Sternapodeme U-shaped, 215–220 µm wide. Lateral sternapodeme thin and straight, located lateroventrally to the sternapodeme, 348–352 µm long. Phallapodeme elongated, with enlarged shoe-shaped apex, 386–390 µm long. Aedeagal lobe and superior volsella fused together; the paired AL + SVo curve to form a ring-like structure with overlapping ends ( Fig. 2E–F ). Median aedeagal lobe oval and spiniferous, 38–40 µm wide. Inferior volsella poorly developed, appressed to the inner side of the gonocoxite, densely setose. Gonocoxite 686–689 µm long, with elongate setae. Gonostylus widest medially, with a narrower apex and a depression in the proximal third, 407–410 µm long; megaseta 54–56 µm long. HR 1.68–1.69. HV 1.26–1.28.

Ecology and habitat. Adult males of S. annularis sp. nov., were collected in April from a high-mountain waterfall environment at an altitude of 932 m. a. s. l., when the air temperature was below 10°C. This habitat is consistent with the known preferences of the larvae of the Sympotthastia , which inhabit cold running waters and springs ( Saether & Andersen 2013).

Remarks. This new species is morphologically similar to S. takatensis ( Tokunaga, 1936) in the general shape of the gonostylus (widest medially, narrowing towards apex) and the oval median aedeagal lobe. However, S. annularis sp. nov. can be clearly distinguished by the absence of an anal point (present in S. takatensis ), the slender, nonenlarged distal end of the fused AL + SVo structure (distal part of superior volsella golf-club shaped in S. takatensis ), and the distinctly enlarged, shoe-shaped apex of the phallapodeme (only slightly expanded in S. takatensis ).

Distribution. Hubei Province, Oriental China.

Figures

FIGURE 1. Sympotthastia annularis sp. nov., male imago (A–G). A. adult male habitus (Scale bars = 2 mm). B. head. C. apex of antenna. D. maxillary palp. E. thorax. F. wing. G. hind tibial comb (Scale bars = 0.5 mm).

FIGURE 2. Sympotthastia annularis sp. nov., male imago (A–E).A. image of hypopygium, ventral view (Scale bars = 0.2 mm). B. image of the dorsal part of the hypopygium showing absence of anal point (Scale bars = 0.5 mm). C. hypopygium, dorsal view. D. hypopygium, ventral view. E & F. sclerotized structures of the hypopygium (AL: aedeagal lobe; SVo: superior volsella; MAL: median aedeagal lobe; Pha: phallapodeme).