Chaetocladius castellae 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 : 16-17

Chaetocladius castellae Moubayed-Breil sp. n.

Material examined.

Holotype. Switzerland: Gletschboden alluvial plain, streamlet and springs located close to the upper catchment of the Rhône River, upstream to the Mutt stream confluence (station U2), altitude 1800 m, 30.IX.1998; 46°34'15.466"N, 8°22'47.054", 1 male adult, leg. B. Lods-Crozet. Environmental data of Rhône water are: crystalline water, conductivity 3.3-17.8 µS /cm; temperature 2-4 °C during late spring to late summer (June-September).

Paratypes. Switzerland: Mutt stream (Station M4), altitude 2100 m. 07.VIII.1997, 46°34'04.946"N, 8°24'17.159"E, 2 male adults, leg. B. Lods-Crozet. Environmental data of Mutt stream water are: crystalline water, conductivity: 61-183 µS /cm; temperature: 1-8 °C during late spring to late summer (June-September). In the streamlet and rheocrenes 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 00460692) and one paratype (on slide) are deposited in the collections of the ‘Musée cantonal de Zoologie, Palais de Rumine, 6 place de la Riponne, CH-1014 Lausanne, Switzerland. Remaining paratype (on slide) is deposited in the collection of the senior author.

Diagnosis.

C. castellae sp. n. is separated from its nearest species ( C. insolitus and C. muttensis sp. n.) by the following main characters: nearly similar shape of tergite IX, which bears a long nose-like dorsally projecting lamella-like structure; long triangular anal point; large inferior volsella; sinuous gonostylus. However, C. castellae sp. n. can be separated from the two previously cited species in having: palpomere 3 bearing 3-4 sensilla clavata (tubule-like) grouped in a ring; dorsal projecting lamella on tergite IX (more strongly projecting upwards), which bears 5-6 setae on ventral side; anal point long and triangular bearing 13-15 dorsal setae on its basal area and 5-6 smaller setae placed on proximal part; gonocoxite markedly swollen medially and bearing 1 row of 7-8 setae on inner dorsal margin, apex of inner dorsal margin with (or without) a distinct triangular to sub-rectangular tubercle; inferior volsella long, tongue-like, downwardly extending to distal part of gonocoxite; gonostylus nearly linear and typically sinuous.

Description.

Male imago (n = 3 male adults; Figs 1-4, 9-18). Small sized Chaetocladius species. Total length 3.00-3.10 mm. Wing length 1.87-1.88 mm (markedly short). General colouration contrasting brown to dark brown. Head dark brown, antennae pale; thorax contrasting brown to dark brown, mesonotal stripes distinctly dark brown; wing pale; legs brown. Tergites I-VIII brown; anal segment brown to dark brown.

Head. Eyes bare, hairs present on median part of inner eye margin. Temporals consist of 10 setae including 6 inner and 4 outer verticals. Antenna 650-660 µm long, 13-segmented; length (µm) of segments: 1, 50; 2-12, 30-35 (nearly sub-equal); last flagellomere 150-160; apex of last flagellomere (Fig. 1) moderately clubbed, bearing 1 pre-apical seta and numerous sensilla chaetica; antennal groove beginning on segment 3 and reaching ultimate flagellomere; AR 0.30-0.40. Clypeus (Fig. 3) broad, nearly rectangular, cup-like in shape with rounded sides and bearing 12 setae in 3 rows. Palp 5-segmented; length (µm) of segments 1-5: 40, 45, 115, 120, 135; palpomere 3 (Fig. 2) with sensilla clavata including: 4-5 sparsely distributed and 3-4 (tubule-like) grouped in a ring which is placed on distal part. Thorax. Antepronotum (Fig. 4) well developed with fused lobes, lateral antepronotals 4-5 grouped close together; acrostichals consist of 15-16 short setae starting close to antepronotum and placed in 1-2 rows; dorsocentrals 10-11 placed in 1-2 rows; humeral pit ovoid, without contrasting spots; prealars 4-5 in 1 row; supralars absent. Scutellum with 6 uniserial setae. Wing. Brachiolum with 1 seta. Membrane densely covered with coarse punctuation. Distribution of setae on veins: R, 15-17; R1, 2-3; R2+3 12-16; remaining veins bare. Squama with 5 uniserial setae. Legs. Tibial spurs of PII and PIII are Chaetocladius -type, with prominent and projecting apicolateral denticles. Sensilla chaetica present on: tibia and tarsomeres ta1-ta2 of PI; tibia and tarsomeres ta1-ta3 of PII; tibia and tarsomere ta1 of PIII. Length (µm) and proportions of legs as in Table 1.

Hypopygium in dorsal, ventral and lateral view as in Figs 9-10; ventral view (Fig. 10) with tergite IX and anal point removed. Tergite IX broadly sub-rectangular with nearly straight posterior margin; basal median area with a characteristic lamella-like structure which is orally directed and markedly visible in lateral view (Figs 9, 11, 17-18); dorsal lamella-like structure is cup-like in dorsal view and a long nose-like shape in lateral view, bearing 5-7 setae place on ventral side (dorsal side lacking setae); presence of 6-8 setae near the posterior margin (3-4 on each side of base of anal point). Anal point (Figs 9, 12, 17) about 90-95 µm long, maximum width at base 30 µm, reaching base of lobe of inferior volsella; basal part large, cup-like, bearing 13-15 dorsal setae including 5-6 smaller and placed on proximal part; median and distal part uniformly elongated and distinctly parallel-sided between base and apex, with an average of 15 µm wide; distance between base of the lamella and base of anal point 35 µm. 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 a distinct rounded oral projection on each side; lateral sternapodeme broad; phallapodeme slender and sinuous medially at joint with lateral sternapodeme. Virga indistinct. Gonocoxite 240-250 µm long, markedly broad medially where maximum width is about 85-90 µm; slightly truncate apically; inner dorsal margin (Fig. 9, 15, 17) markedly swollen medially and with 1 row of 7-8 curved setae, apex of inner dorsal margin bearing a characteristic conspicuous tubercle (triangular to sub-rectangular); ventral inner margin (Fig. 10) with 7-8 inwardly directed setae. Inferior volsella 160 µm long, 75 µm maximum width, clearly visible in both dorsal and ventral view; tongue-like and posteriorly extending from base of gonocoxite till its distal part; posterior margin distinctly straight, apical inner part nose-like and entirely hyaline in both dorsal and ventral sides; distal outer margin weakly separated from inner margin of gonocoxite. Gonostylus (Figs 13, 16) 140-145 µm long, maximum width 40-45 µm; nearly linear with both anterior and posterior margins markedly sinuous; crista dorsalis low and distinct, bearing several short orally directed setae; megaseta 18-20 µm long, conspicuous and slightly bent outwards.

Taxonomic position.

C. castellae sp. n. keys near C. insolitus and C. muttensis sp. n. based on the following resembling characters: presence of dorsal long projecting lamella-like structure; long triangular anal point; large inferior volsella; sinuous gonostylus. However, C. castellae sp. n. can be separated from the two previously cited species by the following main differentiating features: dorsal lamella-like structure on tergite IX is more strongly projecting and bearing setae on ventral side (Figs 9, 11, 12, 17-18), while it is entirely bare in C. insolitus ( Caspers 1987, Figs 3-4) and C. muttensis sp. n. (Figs 58, 62, 65); distal part of inferior volsella differently figured in C. muttensis sp. n. (Figs 58-59, 65); gonostylus typically sinuous anteriorly and posteriorly (Figs 13, 16), while it is narrowing distally and bearing a typical nose-like expansion placed posteriorly in C. muttensis sp. n. (Figs 58, 63-65).

Etymology.

The new species is named castellae in honour to our colleague Dr. Emmanuel Castella, who worked closely together with B. Lods-Crozet on the AASER project (AASER: Alpine and Arctic of Streams Ecosystem Research) during three years (from 1996 to 1998). He is currently senior research scientist at the University of Geneva and at the head of a research group, which focuses on aquatic invertebrate ecology.

Ecology.

Crenophilous species inhabiting cold mountain springs and cold streams with crystalline to calcareous water. Emergence: from July to early September.

Geographical distribution.

Only known from its type locality: Central Swiss Alps.