Chaetocladius (Chaetocladius) tonitrus, Namayandeh & Hudson & Bogan & Hudson, 2024

Namayandeh, Armin, Hudson, Patrick L., Bogan, Daniel L. & Hudson, John P., 2024, Chironomidae (Diptera: Insecta) of Alaska, USA, with descriptions of new species and a checklist, Zootaxa 5511 (1), pp. 1-95 : 27-28

Chaetocladius (Chaetocladius) tonitrus sp. nov. ( Fig. 3C, F, I, L, O )

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Type materials. Holotype male; USA, Alaska, Juneau, Thunder Mountain ; 6.vi.2012; 58.3846, -134.5220; leg. J. Hudson; dep. UAM.

Etymology. The new species is named after its type locality, Thunder Mountain. The word “ tonitrus ” is Latin, meaning thunder.

Diagnosis. The adult male of C. tonitrus can be distinguished from other species of Chaetocladius by the combination of the following characteristics: Large species; temporal setae around 10; last antennal flagellomere with 8 sensilla chaetica; AR 1.7; third palpomere with 9 sensilla clavata in 3 rows; dorsocentrals 8; squama of the wing with 12 setae, costa of the wing barely extended beyond R 4+5, and wing microtrichia visible at 40 ×; anal point prominent, triangular, and wide; tergite IX setae on tapered tubercles; virga consist of two long and narrow spines; sternapodeme arched; inferior volsella bilobed, the anterior lobe with a small bulging nose, posterior lobe more circular, inferior volsella close to anterior 1/3 rd of gonocoxite; gonostylus narrow and slightly bent apically, crista dorsalis slightly bulging at the basal half.

Male (n = 1)

Total length 4.8 mm; wing 2.4 mm long and 0.9 mm wide.

Coloration of mounted specimen. Head, thorax, abdomen, and legs brown. Halteres and wings greyish.

Head. Eyes bare, with short wedge-shaped dorsomedial extension. Tentorium 195 μm long, narrow and pointed apically, tentorial pit close to apex ( Fig. 3C ). Coronal setae 4. Temporal setae around 10 including 2 outer and 9 uniserial orbitals. Antenna with 13 flagellomeres, plume well-developed, last segment with around 8 sensilla chaetica, each of segments 2 and 3 with 2 sensilla chaetica, AR 1.7. Clypeus rectangular, bearing 4 setae, clypeus 82 μm long and 159 μm wide (maximum), clypeus setae 175 μm long. Palpal segments lengths (in μm): 92, 68, 198, 173, 268; third palpomere with 9 sensilla clavata in 3 rows.

Thorax. Acrostichals 14, dorsocentrals 8 in single row, prealars 4, antepronotal lobes with 6 setae laterally. Humeral pit developed, small with several pits.

Wing ( Fig. 3F ). Anal lobe squared. Squama with 12 setae. Brachiolum with 1 seta, R with 19 setae, R 1 with 3 setae, R 4+5 with 9 setae, other veins bare. Costa extension 42 μm long. Microtrichia visible at 40 ×.

Legs. Fore tibial spur 91 μm long, mid tibial spurs 37, 33 μm long, hind tibial spurs 79, 32 μm long, hind leg comb with around 24 spines. Hind tibia spur as in Fig. 3I . Pseudospurs present on mid and hind tarsal segments, two on tarsal segments 1–2 and one on 3. Pulvilli developed but small. Mid and hind trochanter with keel. Lengths and proportions of legs as in Table 4.

Hypopygium ( Fig. 3L ). Tergite IX with around 14 simple setae close to the anal point, setae on tapered tubercles. Anal point prominent, triangular, and wide ( Fig. 3L & O ). Virga consists of two long and narrow spines ( Fig. 3L ), 95 μm long. Sternapodeme arched, 126 μm long. Phallapodeme 97 μm long, with narrow and wavy sclerotization extending to the aedeagal region ( Fig. 3L ). Inferior volsella bilobed, the anterior lobe with a small bulging nose, posterior lobe more circular, anterior lobe covered in simple setae, inferior volsella close to anterior 1/3rd of gonocoxite. Gonocoxite 244 μm long. Gonostylus narrow and slightly bent apically, crista dorsalis slightly bulging at the basal half, gonostylus 109 μm long, megaseta 11 μm long. HR 2.2, HV 4.4.

Remarks

The genus Chaetocladius Kieffer, 1911 is divided into two subgenera Amblycladius Kieffer, 1923 and Chaetocladius Kieffer, 1911 , and several species groups within the subgenus Chaetocladius , sustained only by the characteristics of immatures. However, adult characteristics may not hold for these groupings ( Andersen et al. 2013b; Cranston & Martin 1989; Stur & Spies 2011; Wang et al. 2012). Combination of single gonostylus without basal or outer swellings, developed crista dorsalis and megaseta, well-developed inferior volsella and virga place C. kimfrangosi , C. mendenhallensis , and C. tonitrus in subgenus Chaetocladius .

All three species have a long, bifid virga, with C. kimfrangosi and C. mendenhallensis having hyaline lamellas adjacent to their virga. All three species have well-developed and long anal points with C. mendenhallensis , and C. tonitrus anal points being wide as well. C. tonitrus has additional distinguishing tubercles adjacent to its anal point on the posterior of tergite IX. C. mendenhallensis , and C. tonitrus additionally, have a distinguishing narrow and wavy sclerotization of phallapodeme that extends to the aedeagal region.

The gonostylus of C. kimfrangosi resembles that of Chaetocladius (Chaetocladius) tenuistylus Brundin, 1947 and the anal point resembles that of Chaetocladius (Chaetocladius) egorych Makarchenko & Makarchenko, 2017 . However, C. kimfrangosi differs from both species based on the shape and size of virga and inferior volsella. The gonostylus of C. mendenhallensis resembles that of Chaetocladius (Chaetocladius) holmgreni (Jacobson, 1898) , Chaetocladiues (Chaaetocladius) lencioniae Moubayed-Breil, 2018, Chaetocladius (Chaaetocladius) otujiprimus Sasa & Okazawa, 1994 , and Chaetocladius (Chaetocladius) spiridonovi Krasheninnikov, 2022 . However, C. mendenhallensis differs from these species based on the shape and size of the sternapodeme, virga, anal point, and inferior volsella. C. tonitrus has some similarities to Chaetocladius (Chaetocladius) antipovae Makarchenko & Makarchenko, 2011 , particularly the shape of the virga and anal points. However, the two species differ in shape and size of inferior volsella and gonostylus, and the presence of tubercle on the posterior of tergite IX.

Figures

FIGURE 3. Chaetocladius (s.s.) frangosi sp. nov. (A, D, G, J, M); Chaetocladius (Chaetocladius) mendenhallensis sp. nov. (B, E, H, K, N); Chaetocladius (Chaetocladius) tonitrus sp. nov. (C, F, I, L, O), adult males. A–C. tentorium, D–F. wing, G–I. hind tibia spur, J–L. hypopygium. Scale bars are 50 µm.