Chaetocladius macunensis Moubayed-Breil

Moubayed-Breil, Joel & Lods-Crozet, Brigitte, 2018, On the genus Chaetocladius s. str. Kieffer, 1911 from Switzerland with descriptions of five new relic species occurring in glacial alpine springs and streams (Diptera, Chironomidae), Alpine Entomology 2, pp. 15-34 : 21-22

Chaetocladius macunensis Moubayed-Breil sp. n.

Material examined.

Holotype. Switzerland: Macun cirque, streamlet and rheocrenes, left shore of Immez Lake, alt. 2616 m, 27.VII.2013; 46°43'39.678", 10°07'55.764"E, 1 male adult, leg. B. Lods-Crozet. Environmental data from inlet of Immez Lake: crystalline water, conductivity 5.9 µS /cm; temperature 11.6 °C, pH 6.7 ( Robinson and Oertli 2009).

Paratypes. 3 male adults, same locality and data as for holotype.

Holotype (mounted on 1 slide; GBIFCH 00460690) is deposited in the collections of the ‘Musée cantonal de Zoologie, Palais de Rumine, 6 place de la Riponne, CH-1014 Lausanne, Switzerland. Paratypes are deposited in the collection of the senior author.

Diagnosis.

Based on the unusual and unique shape of the inferior volsella, C. macunensis sp. n. can be easily separated from other members of the Chaetocladius genus by the following characters: clypeus semi-circular bearing 7 setae placed in 1 row along an arc line; antenna and ultimate flagellomere relatively short (respectively 600-660 and 130-200 µm long), apex distinctly clubbed and bearing 1 pre-apical seta, AR markedly low (0.25-0.35); tergite IX sub-triangular and lacking dorsal setae; anal point triangular, uniformly narrowed, apex rounded, base with 6 setae inserted dorsolaterally (3 on each side); virga horseshoe-shaped, median tooth sinuous and S-like in shape; gonocoxite markedly swollen medially and distally, inner dorsal margin without stout setae, inner ventral margin swollen medially; inferior volsella consists of 1 single large and typical lobe, which bears numerous strong stout setae on its inner margin; gonostylus elongated and nearly linear, anterior side covered with setae, posterior margin nearly straight.

Description.

Male imago (n = 2 male adults; Figs 45-57). C. macunensis sp. n. is one of the smallest species of Chaetocladius . Total length 3.55-3.65 mm. Wing length 1.35 mm. General colouration contrasting brown to dark brown. Head yellowish to brown; antennae and pedicel dark brown; thorax contrasting brown to dark brown, mesonotal stripes distinctly dark brown; wing transparent; legs brownish with tarsomeres ta5 dark brown. Abdomen including anal segment entirely brownish.

Head, thorax and tergite I as in Fig. 45. Eyes mostly bare, extreme posterior part with few hairs; inner mar gin bare. Temporals consist of 4 uniserial setae comprising only inner verticals, outer verticals absent. Antenna 730-800 µm long, 13-segmented; ultimate flagellomere (Fig. 46) 130-200 µm long, relatively short; apex of last flagellomere distinctly clubbed, bearing 1 pre-apical seta and curved sensilla chaetica; segments 11 and 12 each about 20 µm long; antennal groove beginning on segments 3 and reaching ultimate flagellomere; antennal ratio markedly low, AR 0.25-0.35. Clypeus (Fig. 48) 125 µm maximum width and 75 µm high, nearly rectangular with rounded sides, bearing 7 setae placed anteriorly in 1 row along an arc line. Palp 5-segmented; first and second palpomeres nearly fused; length (µm) of segments: 15, 55, 105, 115, 160; palpomere 4 distinctly broadened (37 µm maximum width); palpomere 3 (Fig. 47) with 4-5 sensilla clavata. Thorax. Antepronotum (Fig. 49) well developed with gaping lobes, lateral antepronotals 4-5; acrostichals 12-13, short and starting close to the antepronotum; dorsocentrals, 15-16 in 1 row; prealars 4-5; humeral pit ovoid, indistinct. Scutellum with 7 uniserial setae placed along an inversed arc-like (1 medially and 3 on each side of it). Wing. Brachiolum with 1 seta. Membrane densely covered with coarse punctuation. Distribution of setae on veins: R 11; R1 3; R2+3 6-7 placed distally; R4+5 0. Squama composed of 38-41 alternate long and short setae placed in 1 row. Legs. Tibial spurs of PII and PIII are Chaetocladius -type, with prominent apicolateral denticles. Sensilla chaetica (Fig. 50) present on tarsomeres ta1-ta4 of PI, PII and PIII. Length (µm) and proportions of legs as in Table 4.

Hypopygium in dorsal, ventral and lateral view as in Figs 52-57; ventral view (Fig. 53) with tergite IX and anal point removed. Tergite IX broadly triangular and narrowed posteriorly till base of anal point, lacking dorsal setae. Anal point (Figs 51-52, 57) about 60-65 µm long, 15-20 µm maximum width at base, reaching half of inferior volsella length; triangular, uniformly narrowed towards apex which is slightly pointed; base markedly truncate bearing an obtuse prominence which is only visible in lateral view (Fig. 51, 57), presence of 6 setae inserted dorsolaterally (3 on each side). Laterosternite IX with 5 setae on each side, posterior margin with 1 lobe placed near the base of anal point. Transverse sternapodeme rounded with distinct oral projections placed laterally, lateral sternapodeme distinctly short; inner margin of phallapodeme with a median triangular projection, outer margin weakly swollen at joint with lateral sternapodeme. Virga (Fig. 52, 54) distinctly horseshoe-shaped, 15-17µm maximum width; base sub-circular, 15 µm maximum width; median tooth about 20-22 µm long, sinuous and S-like in shape. Gonocoxite 210-215 µm long, maximum width 80-85 µm; in dorsal view (Fig. 52) markedly swollen medially and distally, inner dorsal margin lacking strong stout setae; in ventral view (Fig. 53), the inner margin is swollen medially and bearing 7 stout setae; inferior volsella (Fig. 52, 57) 60-65 µm long, 15-18 µm maximum width, consists of 1 single large lobe, swollen medially and slightly narrowed distally (distinctly visible in dorsal and lateral view, Figs 52, 57), with numerous setae placed on its inner margin. Gonostylus (Figs 55-57) 105-110 µm long, maximum width 25 µm; uniformly elongated, anterior side covered with small setae; posterior margin nearly straight, ending with distinct tooth; crista dorsalis low to nearly absent; megaseta 21-23 µm long, conspicuous and slightly bent inwards.

Taxonomic position.

C. macunensis sp. n. can be easily separated from its nearest species ( C. tenuistylus , sensu Makarchenko and Makarchenko 2004, Fig. 10) by the following main distinguishing characters: ultimate flagellomere relatively short (130-200 µm long), apex clubbed and bearing 1 pre-apical seta (Fig. 5), antennal ratio markedly low (0.25-0.35); tergite IX sub-triangular and lacking dorsal setae; anal point triangular with a truncate prominence (obtuse angle) placed near the base which is only visible in lateral view (Figs 51, 57); virga typically horseshoe-shaped, base circular with its 2 apices distinctly curved inwards, median tooth S-like in shape; anal point triangular and tapering distally; inferior volsella consists of a large lobe which is typically swollen medially and slightly narrowed distally; gonostylus elongated and nearly linear, anterior side covered with setae, posterior margin nearly straight.

Etymology.

The new species is named macunensis after the Swiss Alpine cirque of Macun, which was annexed to the Swiss National Park in 2000 (canton of Graubunden).

Ecology.

C. macunensis sp. n. is apparently confined to cold glacial streams and the inflow section of lakes delimited by the Macun cirque where water is typically crystalline. Emergence is recorded from July to early September.

Geographical distribution.

A typical biogeographic representative of Alpine high mountain springs and glacial streams located in the eastern Swiss Alps area. Currently, C. macunensis sp. n. is only known from the Macun cirque.