Chaetocladius muttensis 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 : 22-27

Chaetocladius muttensis Moubayed-Breil sp. n.

Material examined.

Holotype. Switzerland: upper basin of the Mutt glacial stream (station M5), altitude 1800 m, 03.VIII.1997, 46°34'12.347"N, 8°22'51.363", 1 male adult, leg. B. Lods-Crozet. Environmental data of Mutt stream water are: crystalline to calcareous water, conductivity 61-183 µS /cm; temperature: 1-8 °C during late spring to late summer (June-September).

Paratype. Switzerland: upper basin of Mutt stream (station M4), altitude 2100 m, 09.VIII.1997, 46°34'04.946"N, 8°24'17.159"E, 1 male adult, leg. B. Lods-Crozet. Environmental data of Mutt stream water are: crystalline to calcareous water, conductivity 61-183 µS /cm; temperature: 1-8 °C during late spring to late summer (June-September). In the streamlet and springs located close to station M4, conductivity ranged between 103 to 253 µS /cm; temperature 4.4 to 14.8 °C ( Ilg et al. 2001).

Holotype (mounted on 1 slide; GBIFCH 00460695) is deposited in the collections of the ‘Musée cantonal de Zoologie, Palais de Rumine, 6 place de la Riponne, CH-1014 Lausanne, Switzerland. The single paratype is deposited in the collection of the senior author.

Diagnosis.

C. muttensis sp. n. can be separated from its nearest species ( C. insolitus and C. castellae sp. n.) by the following characters: tergite IX bearing a characteristic dorsal lamella-structure which is bare and slightly projecting close to the dorsal side of tergite IX; anal point triangular, widely broad at base and bearing 6 setae at base (3 on each side); virga faint but present, consists of 3 long spines; inferior volsella tongue-like with distal outer margin well separated from inner margin of gonocoxite; inner margin of gonocoxite not swollen medially and lacking row of strong setae; gonostylus gradually narrowing distally, anterior area with a characteristic undulate line placed distally and reaching base of megaseta, posterior margin with a typical lob-like expansion placed medially and directed downwards.

Description.

Male imago (n = 2 male adults; Figs 5, 6, 8, 58-65). A medium sized species, total length 2.90-3.00 mm. Wing length 1.60-1.75 mm (markedly short). General colouration faintly contrasting brown to dark brown. Head including palpomeres, clypeus and antennae brown to pale brown; thorax brown to dark brown, mesonotal stripes distinctly dark brown; wing pale; legs brown to dark brown. Tergites I-VIII and anal segment brown to dark brown.

Head. Eyes bare, hairs absent on median part of inner eye margin. Temporals consist of 8 setae including 5 inner and 3 outer verticals. Antenna 575-585 µm long, 13-segmented; last flagellomere (Fig. 5) 135-145 µm long, well clubbed, pointed apically, bearing numerous sensilla chaetica apically and lacking pre-apical seta; antennal groove beginning on segment 3 and reaching ultimate flagellomere; AR 0.30-0.35. Clypeus (Fig. 8) trapezoidal with straight sides, bearing 8-10 setae in 2 rows. Palp 5-segmented; length (µm) of segments 1-5: 30, 35, 105, 125, 180; palpomere 3 (Fig. 6) with 4-5 sparsely distributed sensilla clavata. Thorax. Lateral antepronotals 4-5; acrostichals 8-9, short and starting close to antepronotum; dorsocentrals 12-13 in 1-2 rows; prealars 4-5; humeral pit ovoid, lacking contrasting spots. Scutellum with 8 setae placed in 1 row. Wing. Brachiolum with 1 seta. Membrane densely covered with coarse punctuation. Distribution of setae on veins: R, 14-15; R1, 1-2; R2+3 12-13; remaining veins bare. Squama with 5-6 uniserial setae. Legs. Tibial spurs of PII and PIII are Chaetocladius -type, with projecting apicolateral denticles. Sensilla chaetica present on: tibia and tarsomeres ta1- ta4 of PI; tibia and tarsomres ta1-ta3 of PII; tarsomres ta1- ta4 of PIII. Length (µm) and proportions of legs as in Table 5.

Hypopygium in dorsal, ventral and lateral view as in Figs 58-65; ventral view (Fig. 59) with tergite IX and anal point removed. Tergite IX broad, sub-rectangular with nearly semi-circular to straight posterior margin; basal median area with a characteristic lamella-like structure which is weakly projecting and markedly vis ible in lateral view (Fig. 62); dorsal lamella-like projection 45-50 µm long, maximum width 55-60 µm at base, wide cup-like in dorsal view (Figs 58, 65) and long finger-like shape in lateral view (Fig. 62), bare in both dorsal and lateral sides; presence of 14-15 setae placed medially and near the posterior margin. Anal point (Figs 58, 62, 65) about 80-90 µm long, maximum width at base 16-18 µm, uniformly elongated and reaching distal part of inferior volsella; horizontally straight (Figs 58, 62) or occasionally projecting upwards (Fig. 65); basal part wide cup-like bearing 6 setae (3 on each side); parallel-sided medially and distinctly narrowing between median part and apex. Laterosternite IX with 5 lateral setae on each side, posterior margin distinctly bi-lobed (lobes visible on each side of the base of anal point). Transverse sternapodeme arc-like, with distinct tubercle-like oral projections; lateral sternapodeme relatively short; phallapodeme projecting inwards medially. Virga (Figs 59, 60-61) faintly present, consist of 3 long curved spines. Gonocoxite about 250 µm long, broad medially where maximum width is about 80 µm; apex of inner margin distinctly rounded and projecting inwards; ventral side (Fig. 59) wider at base and narrowed distally, inner margin with 10-11 inwardly directed setae. Inferior volsella about 110-115 µm long, 55-60 µm maximum width; long rectangle-shaped and extending from base of gonocoxite to its distal part which is markedly truncate; distal part tongue-like, well separated from the inner margin of gonocoxite (separating part is well visible in both dorsal and ventral view, Figs 58-59); posterior margin bent inwards; apical inner part nose-like, bare and entirely hyaline in both dorsal and ventral sides. Gonostylus (Figs 58, 63-65) 120-125 µm long, maximum width 40-45 µm; narrowing distally, anterior area with a characteristic undulate line extended from median part to base of megaseta, posterior margin rounded and bearing a typical lobe-like expansion which is placed medially and directed downwards; crista dorsalis weekly developed, swollen proximally and becoming gradually lower distally; megaseta 15-18 µm long, conspicuous and slightly bent outwards.

Taxonomic position.

C. muttensis sp. n. keys near C. insolitus and C. castellae sp. n. from which it can be separated in having: tergite IX with a characteristic dorsal cup-like lamella-structure, bare and slightly projecting (Fig. 62); anal point widely broad at base which bears about 6 setae; virga faint but present, consists of 3 long curved spines; inferior volsella tongue-like with distal outer margin well separated from inner margin of gonocoxite; inner margin of gonocoxite not swollen medially and lacking row of strong setae; gonostylus (Figs 58, 63-65) gradually narrowing, anterior area with a characteristic undulate line, posterior margin with a typical lobe-like expansion placed medially and directed downwards.

Etymology.

The new species is named muttensis after the Swiss Alpine glacial Mutt stream, which is located in the upper basin of the Rhône River in the central Swiss Alps.

Ecology.

C. muttensis sp. n. only occurs in the Mutt glacial stream where larvae are apparently confined to the lotic part of springs and the rhithral (crystalline to calcareous water). Emergence from July to early August. Associated species found in the same locality include: C. laminatus Brundin, 1947; C. cf. longivirgatus Stur & Spies, 2011; C. suecicus (Kieffer, 1916); Heleniella helvetica .

Geographical distribution.

C. muttensis sp. n. is only known from its type locality, which is delimited by the upper basin of the Mutt glacial stream.