Tanytarsus illustris, Dantas & Giłka, 2017

Dantas, Galileu P. S. & Giłka, Wojciech, 2017, New Tanytarsus van der Wulp from the Brazilian Amazonia indicate clues to intrageneric relations (Diptera: Chironomidae), Zootaxa 4294 (2), pp. 281-291 : 282-284

Tanytarsus illustris sp. nov.

( Figs 1 A–F, 4A)

Type material: Holotype, adult male: BRAZIL, Roraima state, Serra da Mocidade (01°42'19"N / 61°47'10"W), 26–27 January 2016, light trap, J.M.C. Nascimento ( INPA).

Derivatio nominis. From Latin illustris (distinctive, brilliant).

Diagnosis. Anal point slender, slightly broadened and notched at mid length, with semitransparent distal extension bearing apical knob. Stem of median volsella with two lamellae: anterior (larger) broadly falciform and posterior (smaller) foliate.

Description. Adult male (n = 1).

Body size and proportions. Total length 3.54 mm. Wing length 1.84 mm. Total length/wing length 1.92. Wing length/length of profemur 1.67.

Colouration. Eyes black. Antenna, head capsule and palp light brown. Scutal vittae, postnotum and anterior edge of preepisternum brown. Ground colour of thorax, scutellum and haltere yellowish. Fore leg: femur and tibia brown, darker at apex; ta1-5 light brown. Mid and hind legs: femora brown, with preapical bands slightly paler; tibiae brown; ta1-5 brownish yellow. Wing membrane with pale brownish undertone. Abdomen light brownish, hypopygium slightly darker.

Head. Eyes bare, with well developed dorsomedian extensions. Antenna with 13 flagellomeres; ultimate flagellomere 510 µm long; AR 0.96. Frontal tubercles absent. Tentorium 163 µm long. Temporal setae 14 on each side. Clypeus with 27 setae. Lengths of palpomeres 1–5 (in µm): 44, 46, 173, 160, 300.

Thorax. Ac 26; Dc 14–15 on each side, uniserial; Pa 5 on each side; Scts 15. Scutum projected anteriorly, overreaching antepronotum.

Wing. Typical of the genus, as shown in Fig. 4 A. All veins and entire membrane below radial veins covered with macrotrichia. Brachiolum with 1 seta. VR Cu 1.16.

Legs. Fore leg tibia with straight slender spur 26 µm long. Tibial combs of mid and hind legs separated; spurs of mid leg unequal: one markedly curved, 33 µm long, second slightly curved, 19 µm long; hind tibia with only one slightly curved spur, 39 µm long. Basitarsus of mid leg with 4 hook-shaped sensilla chaetica. Lengths and proportions of legs as in Table 1.

Hypopygium ( Fig. 1 ). Tergite IX covered with minute microtrichia on entire surface and ca. 15 setae around base of anal point, with distinct hump in median position. Lateral teeth absent. Anal tergite bands V-shaped, slightly sinuous, broadly separated. Anal point strongly elongated (ca. 40 µm), narrowest at base (9 µm), slightly broadened and notched at mid length, with semitransparent distal extension bearing apical knob, anal crests and spinulae absent ( Fig. 1 A, C). Superior volsella elongated (55 µm), slightly narrowed at mid length, with 8–10 setae dorsally and 3 setae on median margin; digitus strongly shortened, in shape of tubercle ( Fig. 1 A, B, D). Stem of median volsella ca. 15 µm long, 10 µm wide at base, with two lamellae: anterior (larger) broadly falciform and posterior (smaller) foliate, arranged as shown in Fig. 1 E. Inferior volsella ca. 90 µm long, robust, slightly S-shaped, with 10–11 strongly curved setae ( Fig. 1 A, B, F). Phallapodeme 110 µm long; transverse sternapodeme 70 µm long, with well developed oral projections. Gonocoxite 147 µm long. Gonostylus 150 µm long, broadest at mid length, evenly tapering to narrow tip. HR 0.98, HV 2.36.

Discussion. The presently proposed hirsutus group includes two species at least: Tanytarsus hirsutus and T. illustris . Adult males of both species are distinct in having the strongly shortened tubercle-shaped digitus and in the median volsella bearing two lamellae: the larger one is broad and falciform, whereas the smaller is foliate. Interestingly, the lamellae are arranged in an inverted configuration in these species, as shown in Fig. 1 E and fig. 2d by Trivinho-Strixino et al. (2015). Tanytarsus hirsutus and T. illustris males are also distinct in strongly elongated anal tergite points lacking crests and spinulae, though the anal point structure in T. illustris is more sophisticated (cf. Fig. 1 A, C and Trivinho-Strixino et al. 2015: fig. 2a, b). The two species also differ each other in size of the body and wing (but AR and legs proportions similar), palp length, head and thorax chaetotaxy, as well as in the tibial armature. Future exploring unknown life stages of the hirsutus group requires comparison of their members with Tanytarsus sp. 40 by Wiedenbrug and Ospina-Torres (2005), as suggested by Trivinho-Strixino et al. (2015).

Ecological notes. The male of Tanytarsus illustris was collected with a light trap in a mountainous region at about 1000 m altitude. The trap was left hanging over a small stream (1–2 meters wide), which had a sandy bed partially covered by decayed leaves from a dense riparian forest. The following physicochemical measurements of the water were taken: pH 6.1, temperature 19.5°C, conductivity 12 µS.

Figures

FIGURE 1. Tanytarsus illustris sp. nov., male. A, B — hypopygium in dorsal (A) and ventral aspect (B); C — anal point; D — superior volsella and digitus (green arrow); E — median volsella; F — inferior volsella (C – F magnified ca. 3 – 4 times relative to A and B).

FIGURE 4. Wing of male: Tanytarsus illustris sp. nov. (A), Tanytarsus insignis sp. nov. (B), Tanytarsus insolens sp. nov. (C).