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)

A description of the male adults of five Chaetocladius s. str. species (C. castellae sp. n., C. lencioniae sp. n., C. lodscrozetae sp. n., C. macunensis sp. n. and C. muttensis sp. n.) is provided based on material collected in some glacial alpine springs and cold streams located in the Swiss Alps (altitude 1800–2700 m). Male adult of the nearest Chaetocladius species known from Europe and neighbouring areas belong to: C. aedeagolobatus Rossaro, Magoga & Montagna, 2017; C. insolitus Caspers, 1987; C. gracilis Brundin 1956; C. antipovae Makarchenko & Makarchenko, 2011; C. dissipatus (Edwards, 1929), C. holmgreni (Jacobson, 1998), C. egorych Makarchenko & Makarchenko, 2017. Although some resemblance can be found between the five diagnosed and described species and other related members of the Chaetocladius genus, the taxonomic position cannot be clarified until current comprehensive work on the genus is complete. Geographical distribution of the five new species is currently restricted to the two Alpine Swiss glacial catchments: upper basins of the Rhône River and Muttbach streams; streams and lakes delimited by the Macun area. This highlights the importance of some high mountain ranges, considered as cold glacial enclaves and hotspots of endemism, in the preservation and persistence of autochthonous alpine relic species. Such species are considered as relevant biogeographic representative and their loss would be biologically indicative of global warming and climate change. Currently, there are only seven recorded Chaetocladius species from Switzerland: C. coppai Moubayed-Breil, 2017; C. laminatus Brundin, 1947; C. cf. longivirgatus Stur & Spies, 2011; C. melaleucus (Meigen, 1818); C. perennis (Meigen, 1830); C. piger (Goetghebuer, 1913); C. suecicus (Kieffer, 1916). Consequently, the description of the five new species increases the total number in the genus Chaetocladius to twelve for this country. Remarks and comments on the taxonomic position, ecology and geographical distribution of the new described species, with key to known male adults from the upper catchment of Rhône River (including Muttbach valley) are provided..


Introduction
Alpine freshwaters areas occurring in mountainous landscapes and high elevation are characterized by severe environment (Ward 1994). The relatively harsh environmental conditions prevailing, such as long winters, thick snow and ice cover, low temperature and limited water productivity, contribute to the settlement of highly The Chironomidae family (Diamesinae and Orthocladiinae in particular) predominates in the high alpine ponds/ lakes and stream network with a large number of species compared to the other macroinvertebrates such as other Diptera, Ephemeroptera, Plecoptera, Trichoptera, Oligochaeta (Milner and Petts 1994, Hieber et al. 2005, Robinson et al. 2007). Most of the alpine studies in hydrobiology were focused on macroinvertebrates inhabiting glacial streams (Milner et al. 2001), which revealed that Chironomidae were predominant and characterized by cold adapted species (Kownacki et al. 2000;Lods-Crozet et al. 2001;Moubayed-Breil and Lods-Crozet 2016;Robinson et al. 2007Robinson et al. , 2016; Moubayed-Breil and Dia 2017). Non-glacial aquatic systems, such as springs were also well represented in high alpine landscapes (Lencioni et al. 2012) but have not received much attention so far. High mountain rheocrenes located in the Swiss Alps mostly consist of sensitive and vulnerable habitats, which give shelter, refuge and sanctuary for populations and species potentially rich in divergent genetic lineages and thus resembling diversity hotspots of global significance (Monaghan et al. 2005). Some cold crenobiontic relic species were found in the pristine headwaters in the Alps including two new recently described species (Chaetocladius coppai Moubayed-Breil, 2017; Heleniella helvetica Moubayed-Breil & Lods-Crozet, 2016) from remote areas in small groundwater resurgences and spring-fed streams located in the upper basin of the Rhône River.
Based on knowledge provided on the taxonomy, geographical distribution and ecology of the known Chaetocladius species from Europe and the Palaearctic Region (Brundin 1947(Brundin , 1956Pankratova 1970;Saether 1980Saether , 1990Caspers 1987, Cranston et al. 1989, Bhattacharyay et al. 1993, Lods-Crozet 1998, Moubayed 1989, Makarchenko and Makarchenko 2001, 2004, 2007, 2011a-b, Langton and Pinder 2007, Lencioni et al. 2007, Zelentsov 2007, Stur and Spies 2011, Ashe and O'Connor 2012, Kobayashi 2012, Wang et al. 2012, Saether and Spies 2013, Makarchenko et al. 2017, Moubayed-Breil 2017, Rossaro et al. 2017, the genus Chaetocladius Kieffer, 1911 currently comprises worldwide about 79 valid species. Based on material collected between 1997-1998 and 2013 in high alpine springs and small cold streams located in the Swiss Alps, we here describe five new species of Chaetocladius s. str for which we discuss the taxonomic position, ecology and geographical distribution. A key to the known male adults from the catchment of the upper Rhône (including Muttbach glacier), with remarks on some related species from the Palaearctic Region are also provided.
The Mutt stream (length: 3600 m) originating from the Mutt glacier (area 0.6 km 2 , altitude 2582-3000 m) represents the major tributary of the upper Rhône catchment. It joins the Rhône River at the upper limit of a floodplain and contributes approximately 10 % (0.62 m 3 .s -1 in 1997) to the Rhône discharge (Knispel and Castella 2003). The upper parts of the Mutt catchment are composed mainly of moraines and bare rocks including a carbonate outcrop. Alpine grasslands are found in the lower parts while Salix spp. and Alnus viridis thickets, together with herbaceous alpine vegetation, are predominant in the floodplain .
The Rhône River alluvial plain "Gletschboden" is located in the upper catchment of the Rhône River. The major water source is the Rhône glacier (area 10.2 km 2 ). Below the glacier snout, situated at an altitude of 2210 m, the Rhône River flows down a 400 m high granite cliff (slope 63 %) and enters an alluvial plain (length: 2000 m). During the last century, the retreat of the Rhône glacier has left valley moraine deposits and a braided channel pattern. The upper part of the Rhône is a kryal segment (Ward 1994) where water temperature rarely exceeds 4 °C. Mean annual discharge of the Rhône in 1998 was 2.88 m 3 .s -1 and its hydrograph reveals a discharge peak in summer with large daily flow fluctuations (Knispel and Castella 2003). Highly diverse thickets of Salix spp. and Alnus viridis and herbaceous alpine vegetation are predominant in the alluvial plain, with some Larix decidua.
The Macun cirque site is a high alpine cirque (> 2600 m), which is located in the Eastern Alps (Swiss National Park). It was annexed to the park in 2000 and currently is an area designed for long-term monitoring of alpine water bodies (springs, streams, ponds, lakes). The region comprises more than 35 small lakes or permanent ponds and around 10 small temporary ponds scattered within two sub-basins. A north basin is fed mostly by snowmelt and groundwater, whereas the south basin is fed by glacial melt from a number of rock glaciers. Precipitation is low, typically being around 850 mm per year. Bedrock geology is crystalline (ortho-gneiss) rock. The area is above the tree line and the drainage area of each pond is characterised by a mixture of two types of land cover, rock and alpine grassland Oertli 2009, Lods-Crozet et al. 2012).
The sites in the Central Alps were investigated three times a year between 1996 and 1998, during the three major annual hydrological phases: in June during snowmelt, in August during ice melt and in September at low water level. The field protocols followed closely those established in the EU-project 'AASER' (Brittain and Milner 2001, Knispel and Castella 2003, Lods-Crozet 2012.

Sampling procedure
Ten sampling points were chosen randomly within each site. Depth, flow velocity and bed sediment composition were recorded at each of the 10 points before benthic sampling. The fauna was then collected into a 250-mmmesh pond net at these points by kick sampling within a 30 × 30-cm area for 30 s. Adult material was collected using Malaise traps which were set up for a minimum of five days. In the Eastern Alps, during summer 2013, a supplementary survey was conducted to complete the standardized monitoring of small water bodies and streams within the Macun cirque . Adult material of the five new described Chaetocladius species was collected for fifteen days using Malaise trap placed in the surrounding area of three lakes (altitude 1800-2700 m). Pupal exuviae were collected with a drift net from the shore.
All samples were preserved in 70 % Ethanol. Material of male adults were cleared of musculature in 90 % lactic acid (head, thorax, abdomen and anal segment) for about 60 to 80 minutes, which can be left overnight at room temperature without any detrimental effect or damage. The specimens were checked under a binocular microscope after 20 minutes in lactic acid to determine how the clearing was progressing. When clearing was complete the specimens were washed in two changes of 70 % Ethanol to ensure that all traces of lactic acid were removed. Compared to clearing with potassium hydroxide, or other clearing solutions, no deterioration of the typical "original" structure is reported by using lactic acid. All examined material was mounted in polyvinyl lactophenol, remaining material including paratypes were preserved in 70 % Ethanol. The eye on one side was dissected from the head, which ensures that the hairs on the inner margin of the eye are more clearly visible. Before the final slide mountings (dorsally) of the type and paratype material, the hypopygium including the IX th tergum, the anal point, the gonocoxite and the gonostylus, were viewed ventrally and laterally to examine and draw from both sides all the necessary details of the species. In particular, the ventral view of hypopygium was illustrated when anal point and tergite IX were removed. Morphological terminology and measurements largely follow Saether (1980) and Cranston et al. (1989) for the imagines.  (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 .

Taxonomy
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.
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 noselike 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 di-rected 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. ( 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. Lods-Crozet. Environmental data of Mutt stream water are: crystalline/calcareous water, conductivity 61-183 µS/ cm; temperature: 1-8 °C during late spring to late summer (June-September). In the streamlet and rheocrenes located near station M4, conductivity ranged between 103 to 253 µS/cm; temperature 4.4. to 14.8 °C ). Paratype. 1 male adult, same locality and data as for holotype.

Chaetocladius lencioniae
Holotype (mounted on 1 slide; GBIFCH 00460691) 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. lencioniae sp. n. keys near the following two species: C. gracilis, based on the shape of both tergite IX and the anal point; C. antipovae, based on the shape of the inferior volsella. However, C. lencioniae sp. n. can be distinguished in having: tergite IX semi-circular; sternite IX typically circle-like in shape; anal point markedly pointed apically and bearing setae on proximal part; virga faint, consists of 2 long teeth; gonostylus massively spherical to bulb-shaped, anterior margin swollen medially, ending in 3 characteristic small teeth comb-like placed close to the base of megaseta, posterior margin rounded, projecting downwards and terminating in a pointed sclerotized apical tooth; crista dorsalis large tooth-like, sclerotized and spherical, smooth with rounded apex, placed pre-apically close to megaseta (clearly visible in dorsal and ventral view).
Description. Male imago (n = 2 male adults; Figs 22-31). Small sized species. Total length 3.75 mm. Wing length 2.15 mm. General colouration contrasting pale brown to dark brown except for the mesonotal stripes, which are reddish dark brown. Head brownish, antennae pale brown, thorax brown with dark brown mesonotal stripes. Wing transparent. Legs brown with dark brown tarsus. Tergites I-V brownish, tergites VI-VIII yellowish, anal segment hyaline to yellowish; gonostylus dark brown in its proximal and median part, dark brown to blackish in its distal part, megaseta and surrounding area dark brown.
Taxonomic position. C. lencioniae sp. n. keys near C. gracilis, based on the shape of both tergite IX and the anal point (Brundin 1956, fig. 87) and C. antipovae, based on the shape of the inferior volsella (Makarchenko and Makarchenko,. However, the new species can easily be separated from other members of the Chaetocladius genus in having: tergite IX semi-circular; sternite IX typically circle-like in shape; anal point markedly pointed apically and bearing setae on proximal part; virga with 2 distinct long teeth; gonostylus spherical to bulbous; anterior margin ending with 3 characteristic pointed teeth (Figs 29-31), comb-like and placed close to megaseta area (clearly visible in both dorsal, ventral and lateral view); posterior margin markedly swollen distally and terminating in a pointed sclerotized apical tooth; crista dorsalis strong tooth shaped, smooth and placed pre-apically close to megaseta.

Etymology.
The new species is named lencioniae in honour of our colleague Dr. Valeria Lencioni from the Museum of Trento (Italy), who is active as curator 'Conservatore' and hydrobiologist in contributing to preserve the biological and ecological quality of water and environment in Trento and surrounding areas.
Ecology. High mountain springs and cold streams with crystalline to calcareous water. Emergence: from July to early September.
Geographical distribution. C. lencioniae sp. n. is only known from its type locality. It can be considered as a typical biogeographic representative of high mountain rheocrenes and cold streams delimited by some Swiss Alpine glaciers.   .
Holotype (mounted on 1 slide; GBIFCH 00460693) and 1 male paratype (on 1 slide; GBIFCH 00460694) are deposited in the collections of the 'Musée cantonal de Zoologie, Palais de Rumine, 6 place de la Riponne, CH-1014 Lausanne, Switzerland. Remaining paratypes are deposited in the collection of the senior author.
Diagnosis. The nearest species to C. lodscrozetae sp. n. are C. dissipatus, C. holmgreni, C. egorych and C. aedeagolobatus Rossaro, Magoga & Montagna, 2017 from which it can be separated in having: clypeus half diamond-like, with V-shaped posterior side, bearing 6 setae placed in 2 rows; palpomere 4 distinctly truncate apically, sensilla clavata present on segment 3 including 5 sparsely distributed and 3 (tubule-like) grouped on a ring placed distally; ultimate flagellomere 465-475 µm long, distinctly clubbed, AR about 1; tergite IX broad and semi-circular with 16-22 dorsal setae placed on its posterior part; anal point long, triangle-like, nearly parallel-sided and distinctly thin between base and apex, dorsally bearing a characteristic massive lamella-like orally directed structure which is markedly visible in lateral view, lamella is cup-like in dorsal view, composed of 2 well separate margins, inner margin linear and bare, outer margin markedly undulated and bearing 7-8 dorsolateral setae, inside area bare; virga typical inversed V-shaped, composed of 6-7 posteriorly directed spines; gonocoxite broad basally and narrowed distally, abruptly tapering before apex; inferior volsella extending from base of gonocoxite to its distal part, consist of 2 lobes (dorsal lobe markedly projecting medially and beak-like in shape, distal part distinctly swollen and pouch-like in shape; ventral lobe swollen basally and tapering distally, ending nearly at tip of gonocoxite, inner ventral margin bearing about 11 strong setae; gonostylus half bulb-shaped ending with a distinct hyaline rounded distal area, anterior side with orally directed small setae, posterior margin markedly rounded bearing a double inner apical margin, anterior margin varies from straight to convex, crista dorsalis low and indistinct. Description. Male imago (n = 4 male adults; Figs 32-44). Medium sized species. Total length 3.80-3.90 mm. Wing length 2.00-2.13 mm. General colouration contrasting brown to dark brown. Head dark brown, antennae pale brown, thorax brown to dark brown, mesonotal stripes distinctly dark brown; wing pale; legs contrasting brown to dark brown. Tergites I-VI/VII brown, tergites VII-VIII and anal segment entirely dark brown.
Taxonomic position. C. lodscrozetae sp. n. keys close to C. dissipatus, C. holmgreni, C. egorych and C. aedeagolobatus from which it can be separated in having: sensilla clavata present on palpomere 3 including 5 sparsely distributed and 3 grouped on a characteristic ring placed distally; tergite IX broad and nearly semi-circular with 10-11 setae on its posterior area, presence of a characteristic massive rounded prominence extending from the median area to base of anal point; anal point elongated and parallel-sided which is distinctly thicker on its proximal half; virga inversed V-shaped, composed of 6-7 posteriorly directed spines; gonocoxite broad basally and narrowed distally, abruptly tapering before apex; inferior volsella extending from base of gonocoxite to its distal part, consist of a large lobe which is pouch-like in shape, inner margin terminating in a hyaline nose-like lobe which is bare and bent downwards; gonostylus nearly semi-circular, distal part of posterior margin hyaline and bare, anterior side with orally directed small setae, anterior margin varies from straight to convex.

Etymology.
The new species is named lodscrozetae in honour of Dr. Brigitte Lods-Crozet from the Cantonal Museum of Zoology of Lausanne (Switzerland), who is still active as researcher and hydrobiologist in contributing to preserve the biological and ecological quality of water and environment in Switzerland.
Ecology. Glacial springs and cold mountain streams with crystalline to calcareous water. Emergence: from July to early September.
Geographical distribution. C. lodscrozetae sp. n. is only known from rheocrenes and lotic habitats delimited by the Gletschboden floodplain, the Mutt stream and streamlet, Swiss Alps, altitude 1800-2100 m.
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 ta 5 dark brown. Abdomen including anal segment entirely brownish.
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.
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.
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.

Key to known adult males of Chaetocladius species from the upper catchment of Rhône River including Muttbach valley (Central Swiss Alps)
1 Tergite IX with a dorsal lamella structure located on median area (Figs 9, 17, 58

Discussion
The nearest Chaetocladius species to the five diagnosed and described species include: C. insolitus for C. castellae sp. n.; C. gracilis and C. antipovae for C. lencioniae sp. n.; C. dissipatus, C. holmgreni, C. egorych and C. aedeagolobatus for C. lodscrozetae sp. n. Based on some specific characters found in the male adult of C. macunensis sp. n (shape of anal point, inferior volsella and virga), this new species can be placed near C. tenuistylus Brundin, 1947 (sensu Makarchenko andMakarchenko 2004, Fig. 10). Although some resemblance can be found between the five new described species and other related members of the Chaetocladius genus, the taxonomic position cannot be clarified until current comprehensive work on the genus is complete.
Worldwide there are actually about 79 known Chaetocladius species, which include the hitherto listed 69 species by Ashe and O'Connor (2012) and the recently described 10 species by: Makarchenko et al. (2017), Mou-bayed-Breil (2017), Moubayed-Breil and Dia (2017), Rossaro et al. (2017). Consequently, the updated previous list of 79 species is upgraded to 84, which currently include the five new described species in this paper.
Geographical distribution of the five new described species is currently restricted to the two Alpine Swiss glacial catchments (Figs 66-68): upper catchment of the Rhône River and Muttbach streams; streams and lakes delimited by the Macun area. Type localities of C. castellae sp. n., C. lencioniae sp. n., C. lodscrozetae sp. n. and C. muttensis sp. n. are delimited by stenothermic springfed rivulets located close to glacial streams (Rhône River, Mutt stream) and the upper Rhône catchment (central Switzerland, alt. 1800(central Switzerland, alt. -2000. C. macunensis sp. n. only occurs in a high-alpine catchment in the Swiss National Park (Macun region, Eastern Swiss Alps, alt. 2550-2700 m).
It is of interest to note that none of the new described species in the present work is identical to any of those described recently from southern side of the Alps (Stur andSpies 2011, Rossaro et al. 2017). This may contrast with a previous statement that the faunae on the two sides of the Alps are similar (Reiss 1968). Nevertheless, it is not really surprising, as the Chironomidae still are quite incompletely known with new species being described continuously from various parts of the word, including from Europe.

Conclusion
The presence of the five new species in some high mountain Alpine ranges of Switzerland highlights the importance of some cold glacial enclaves, considered as hotspots of endemism, in the preservation and persistence of autochthonous and sensitive alpine relic species. Such species are considered as relevant biogeographically representative and their loss would be biologically indicative of the global warming and climate change.