The Chironomidae (Diptera) of Svalbard and Jan Mayen

Non-biting midges of the fly family Chironomidae are extremely abundant and diverse in Arctic regions and are essential components of Arctic ecosystems. Modern identification tools based on documented records of Arctic chironomid species are therefore important for ecological research and environmental monitoring in the region. Here, we provide an updated review of the chironomid fauna of the Svalbard archipelago and the island of Jan Mayen, Norway. Our results show that a total of 73 species distributed across 24 genera in four subfamilies are known from these areas. Our review treats 109 taxa, including nomina dubia and misidentifications. It includes morphological identification keys to all known species as well as photographs of most taxa and DNA barcodes of 66 species. Taxonomic remarks are given for selected taxa, including previous misidentifications and erroneous records. Chironomus islandicus, Tvetenia bavarica, Limnophyes schnelli, Metriocnemus brusti and Metriocnemus fuscipes as well as the genera Allocladius, Corynoneura and Bryophaenocladius are reported from Svalbard for the first time, while Procladius (Holotanypus) frigidus, Stictochironomus psilopterus, Chaetocladius incertus, Orthocladius (Orthocladius) mixtus and Smittia longicosta, previously considered as junior synonyms or nomina dubia, are revived as valid species based on examination of type material or literature. Twenty species within eleven genera are introduced with interim names. Metriocnemus similis is regarded as a junior synonym of Metriocnemus ursinus, and Smittia incerta, Smittia flexinervis and Smittia spitzbergensis are regarded as nomina dubia. Valid taxa no longer considered as part of the Svalbard fauna are Parochlus kiefferi, Arctopelopia barbitarsis, Procladius (Holotanypus) crassinervis, Diamesa lindrothi, Diamesa incallida, Diamesa lundstromi, Chironomus hyperboreus, Sergentia coracina, Camptocladius stercorarius, Chaetocladius dissipatus, Chaetocladius dentiforceps, Chaetocladius laminatus, Chaetocladius perennis, Cricotopus (Cricotopus) humeralis, Cricotopus (Cricotopus) polaris, Hydrosmittia ruttneri, Limnophyes edwardsi, Metriocnemus picipes, Metriocnemus tristellus, Orthocladius (Eudactylocladius) gelidus, Orthocladius (Euorthocladius) thienemanni, Orthocladius (Orthocladius) obumbratus, Orthocladius (Orthocladius) rhyacobius, Paralimnophyes, Paraphaenocladius impensus, Psectrocladius (Monopsectrocladius) calcaratus, Psectrocladius (Psectrocladius) psilopterus, Psectrocladius (Psectrocladius) ventricosus, Smittia lasiophthalma, Smittia lasiops and Zalutschia tatrica.


Introduction
The family Chironomidae, or non-biting midges, is one of the most common and species rich organism groups in freshwater and semi-aquatic habitats [1]. It has members in all biogeographical regions, including the Antarctic mainland, and more than 6000 valid species described world-wide ( [2,3]; Patrick Ashe pers. comm.). As is true for most insect groups, chironomids are considered as better known in some regions than in others. However, even in regions with long taxonomic history,  The first chironomids to be documented from Svalbard were collected by expeditions between 1838 and 1861 and described by Carl Henrik Boheman [25]. Five chironomid species were recorded in the material available to him, of which three are recognised as part of the Svalbard fauna today, either under a senior synonym (Chironomus lugubris Zetterstedt, 1850 = C. polaris Boheman, 1866) or subsequently placed in different genera (Diamesa arctica (Boheman, 1866) and Smittia brevipennis (Boheman, 1866)) (Species were described in Boheman (1865), but names were not available according to the International Code of Zoological Nomenclature until actual publication in 1866.) Concering his remaining two species identifications, one used a name currently regarded as a nomen dubium (Tanytarsus productus (Zetterstedt, 1838)) and the other likely was a misidentification of Smittia aterrima (Meigen, 1818). The list of species from Spitsbergen was revised and increased by August Emil Holmgren who participated in the Swedish expedition to the archipelago in 1868. The expedition was Table 1. Chironomidae (Diptera) species from Svalbard and Jan Mayen with associated DNA barcode records. Specimen records refer to material vouchered in museum collections. Taxa marked with '*' are included in the discussion, x = material examined or analysed by the authors, [ Diamesa bohemani Goetghebuer, 1932 x x x x 8

Keys to the Chironomidae of Svalbard and Jan Mayen
The key to adults includes species that are recorded from Svalbard and Jan Mayen. It is likely that more species from certain genera will be found in the future and caution should be taken in species-level identifications. Although we do not know of reliable records, we included the genera Parochlus, Paralimnophyes and Sergentia in the key of these because they are not unlikely to be found on Svalbard or Jan Mayen. The keys to larvae and pupae are to genus-level only since many species have unknown immature stages and keys could therefore be misleading. Since the characters used in the key to immatures are based on known associations, they might not represent the species on Svalbard very well (e.g., Paraphaenocladius).   6. Outer genitalia with well-developed gonocoxites and mobile gonostyli (e.g., Figure 5f) (males) 7 -Outer genitalia with reduced gonocoxites and one-segmented cerci (e.g., Figure 5e) (females) 11 7. Anal point of hypopygium small (Figure 5f) Diamesa aberrata -Anal point of hypopygium well-developed (e.g., Figure 6c Tanytarsini) 17 -Wing membrane often bare, squama with numerous setae on edge; crossvein RM oblique with R4+5 (e.g., Figures 16a, 19a and 20a) (tribe Chironomini) 25 17. Antenna short with 5-6 flagellomeres; genitalia with cerci, without strongly developed gonocoxites and gonostyli (females) 18 -Antenna plumose with 11 flagellomeres; genitalia with strongly developed gonocoxites and gonostyli (males) 22 18. Small, bright green in colour with brown mesonotal bands; fore leg ratio (LR1) >1.4; mid-and hind tibial combs well separated, each with obvious spur; gonapophysis VIII undivided; parthenogenetic on Svalbard ( Figure 15) Tanytarsus heliomesonyctios -Dark specimens, if greenish in ground colour, always with some brown pigmentation (not bright green); LR1 < 1.4; mid-and hind tibial combs fused (e.g., Figure 12i), without or with at most a minute spur; gonapophysis VIII divided 19. Light olive green ground colour, scutellum and antennae; mid and hind tibial combs with minute spur; dorsomesal lobe of gonapophysis VIII broad ( Figure 14) Paratanytarsus austriacus -If olive green ground colour and scutellum, antenna, fore tibia and maxillary palps with brown pigmentation; dorsomesal lobe of gonapophysis VIII narrow (Genus Micropsectra) 20 20. Wing membrane with setae in apical 1/3 only, no setae in cell m; low tibial combs; completely dark brown ( Figure 13)    Orthocladius spp. (see page 26) 3.1.2. Pupae 1. Anal lobe fringed with taeniate setae, but lacking distinctive macrosetae (e.g., Figure 10.77D in [73]); posterolateral corner of segment VI with sclerotized comb (e.g., figures 10.55E, F in [73],) (subfamily Chironominae) 2 -Anal lobe with or without setal fringe; if fringed, three distinctive macrosetae present on each side; posterolateral corner of segment VI never with comb 7 2. Thoracic horn with multiple branches; tergites IV-V without median patch/patches of spines or spinules (tribe Chironomini) (e.g., Figure 10.77D in [73]) 3 -Thoracic horn not branched (e.g., Figure 10.55C in [73],); tergites IV-V with median patch or paired patches of spines or spinules (tribe Tanytarsini) (e.g., Figure 10.55E in [73]) 5 3. Tip of cephalic tubercle with circular field of spinules (e.g., Figure 10.71A in [73]) Sergentia -Tip of cephalic tubercle without spinules 4 4. Anal lobe without dorsal seta; well-defined posterolateral comb with well-separated robust teeth present on segment VIII (e.g., Figure 10.77E in [73])

Stictochironomus
-Anal lobe with dorsal seta; posterolateral spur or brush of closely adjacent spines present on segment VIII (e.g., Figure 10.6E in [73]) -Wing sheath without pearl row; spines or spinules present in patches on tergite III; tergite IV with two point patches (Figure 12e in [75], Figure 14 in [76]) Micropsectra 7. Thoracic horn well developed, with horn sac and sometimes plastron plate (e.g., Figure 4.5B in [77], figures 5.6A,B and 5.31D,E in [78]) 8 -Thoracic horn present or absent, thin, without horn sac and plastron plate 10 8. Two pairs of frontal setae; sheaths of fore-and midlegs straight, terminating beside recurved hindleg sheath at apex of wing sheath (subfamily Podonominae) Parochlus -One pair of frontal setae; all leg sheaths recurved beneath wing sheath (subfamily Tanypodinae) 9 9. Thoracic horn tubular, without plastron plate; anal lobe triangular with pointed apex. Arctopelopia -Thoracic horn widest in middle, with plastron plate; anal lobe rounded with serrate border towards apical point Anal lobe with a full or partial fringe of setae; fringe setae may be sparse or dense, short or long 13 -Anal lobe without a fringe of setae; anal lobes sometimes absent or greatly reduced 18 13. Thoracic horn absent; lateral setae on tergite III taeniate Corynoneura -Thoracic horn present; lateral setae on tergite III not taeniate 14 14. Tergite IV with discrete spine patches or rows in the median field and/or along the posterior margin (e.g., figures 9.54c and 9.55h in [80])

Discussion
Many of the chironomids encountered on Svalbard are difficult to identify, either due to subtle morphological differences or to the lack of taxonomic revisions. Often, the original literature and vouchered reference material must be consulted, and even then, the results can be ambiguous. In this section, we comment on various observations made and present arguments for the identification (or previous misidentification) of genera and species reported from Svalbard and Jan Mayen. When interesting, we also refer to the known geographical distribution and genetic similarity with DNA barcodes from other populations represented in BOLD.

Parochlus
Parochlus kiefferi and Paralimnophyes sp. were reported from birds' nests on Spitsbergen as "old and damaged" larval head capsules [85]. Apart from these findings, the two genera have never been recorded from Svalbard. We have examined the head capsule remains that were reported by Pilskog et al. [85]. They are in a relatively poor condition but, based on the mentum and very short antennal segment 1, the three specimens identified as Parochlus kiefferi likely belong to Smittia instead. However, we do include Parochlus kiefferi in the key since it is not unlikely that it will be found on Svalbard in the future (we have seen records from the Norwegian mainland, Iceland and Greenland).

Arctopelopia
The species Arctopelopia barbitarsis was recorded in stomach content of Arctic char from lakes on Bear Island by Berg, Finstad, Olsen, Arnekleiv and Nilssen [19] (identified by T. Ekrem). Re-examination of the specimens have revealed that these belong to A. melanosoma (Goetghebuer, 1933). Comparison of DNA barcode data in BOLD shows that the BIN with A. melanosoma (BOLD:AAD2100) containing members from Bear Island, Greenland and Canada is genetically distinct from the group with A. barbitarsis with barcodes from continental Norway and Finland. We have examined two females from Bear Island identified as A. barbitarsis by Edwards [31] and find these conspecific with examined females of A. melanosoma. We thus regard A. barbitarsis as absent from the Svalbard Archipelago.

Procladius
Tanypus frigidus Holmgren, 1869 was originally described from Bear Island (Mount Misery) [26]: p. 48. The name is listed as a junior synonym of Procladius (Holotanypus) crassinervis in the World Catalogue of Chironomidae [2] which other authors have been treated as a subjective synonym of Procladius (Holotanypus) culiciformis (Linnaeus, 1767) [57,86]. DNA barcodes of our specimens from several localities on Bear Island and Spitsbergen cluster nicely with those of specimens from northern Norway but are more than 7% different from specimens in BOLD identified as P. (H.) culiciformis. Moreover, the original description of Tipula culciformis indicate that the specimens Linnaeus described had pale legs [87]: p. 978, while our specimens are completely dark. Tanypus crassinervis was originally described with bare wings [66]: p. 817, which differs from later interpretations of this species, e.g., [47]. Our specimens from Bear Island have moderately hairy wings in the adult males, while female wings have more hairs (Figure 4a,b) and therefore, do not fit the original description. Comparison of DNA barcode data in BOLD, show that there currently are five BINs with the name of P. (H.) crassinervis. Sequences from our Svalbard specimens populate BOLD:AAB9256 together with specimens from northern Canada, Greenland, continental Norway and Finland. The genus and the species group are in need of revision [57], but we choose to keep the name P. (H.) frigidus here since our specimens were collected close to the type locality, and because they clearly best fit the original description under this name. We thus regard previous records of P. (H.) crassinervis from Svalbard to be misidentifications and/or caused by a doubtful synonymy and reinstate the name Procladius (H.) frigidus for specimens associated with the Svalbard population.
Procladius cf. choreus was reported from Londonelva, New Ålesund on Spitsbergen by Lods-Crozet, et al. [88]. As this constitutes an uncertain identification in a genus in need of revision, we currently do not treat P. choreus as present on Svalbard.

Diamesa
Diamesa hyperborea Holmgren, 1869 was originally described from Bear Island [26], and has been documented and DNA barcoded by us. Pedersen [70] and Saether [89] indicated that Diamesa hyperborea (as D. ursus Kieffer, 1919) is present on Spitzbergen. Their distributional records likely originate from Styczyński and Rakusa-Suszczewski [90] who collected larva in a pond near Hornsund. We have been unable to confirm this by examination of specimens and regard the presence on Spitzbergen as questionable since the only known record is based on larvae only.
Diamesa incallida was reported as pupae from Bayelva near Ny Ålesund, Spitsbergen [88]. We have been unsuccessful in locating the vouchers of these records (pers. comm. with Brigitte Lods-Crozet and Valeria Lencioni). Thus, we consider the identification of the single finding of D. incallida as doubtful and regard this species as absent from Svalbard.
Diamesa lindrothi (or "D. cf. lindrothi") apparently has been reported from Svalbard as larva only [20,90,91]. We have not seen material of D. lindrothi from Svalbard or Jan Mayen, and regard the species records based on larva only as doubtful as this species has a morphology very similar to that of Diamesa bertrami and descriptions of D. lindrothi larvae from Svalbard [90] fit well with observations we have made of D. bertrami. We therefore regard D. lindrothi as not present on Svalbard until its occurrence there is proven.
Diamesa lundstromi Kieffer, 1918, was recently reported as present on Svalbard [92,93]. The species' name originates from Kieffer [94] as a new name for specimens from Bear Island and Spitsbergen previously assigned to Diamesa arctica (Boheman, 1865) in Kieffer and Lundbeck [71]. Diamesa lundstromi is currently considered as a nomen dubium [2]. We have not seen material that could help clarify this species name, nor been able to locate the type material in Zoologisches Forschungsmuseum Alexander Koenig in Bonn, Germany.

Pseudokiefferiella
The genus Pseudokiefferiella has been treated as monotypical, the only valid species being P. parva (Edwards, 1932) originally described from Scotland. The species was recorded from Spitsbergen as larvae [91]. However, we collected one female from Spitsbergen that is morphologically and genetically different from continental P. parva; its DNA barcode clusters with those of numerous females from Greenland and more distantly (3.9% divergent) with a male from Finnmark. We believe the larvae collected by Losos and Kubíček (1988) belong to this species, and that it is likely new to science. Material from Greenland and northern North America should be considered before description as there are indications of additional taxa that should be treated simultaneously [15]: p. 617).

Chironominae, Tanytarsini
Tanytarsus Tanytarsus heliomesonyctios Langton, 1999 was originally described from Ellesmere Island in Arctic Canada [74]. Stur and Ekrem [10] recorded the species from Spitsbergen and described the larva based on associations through DNA barcodes. Although all specimens collected in the high Arctic so far have been females and support the assumption that T. heliomesonyctios is a parthenogenetic species, we have a DNA barcodes from a male collected in northern Norway (Porsanger, Finnmark) that clusters with females from the Arctic as well as with specimens throughout Canada (BIN BOLD:AAC2863). Adult males were recently described from northeast Russia [95]. We suspect that the species is facultatively parthenogenetic with males appearing at lower latitudes.

Chironomus
The species Chironomus hyperboreus originally described from Greenland [96,97] has been reported from Spitsbergen and Bear Island [26,31,98]. Some authors considered the name as a senior synonym of Chironomus islandicus [99], but Pedersen [65] provided convincing evidence for separate species. We have DNA barcodes of C. hyperboreus specimens from continental Norway that match with populations from Greenland and Canada in BOLD, and DNA barcodes of populations from Bear Island and continental Norway that match a population from Iceland identified as C. islandicus. The COI-sequences of the two groups differ by approximately 5% K2P-distance. Moreover, our specimens from Bear Island agree morphologically with the diagnostic characteristics of C. islandicus discussed by Pedersen [65]. Although we cannot be sure about the identity of previous records of C. hyperboreus from Svalbard, we think there is reason to believe that these were based on misidentifications of C. islandicus, since the two species are morphologically very similar and the distinction between them was first properly presented by Pedersen [65]. Chironomus islandicus was previously known from Iceland, Greenland and Finland [65,86]. The larvae of both C. islandicus and C. hyperboreus are of salinarius-type, i.e., lack the ventral and lateral tubuli seen in many Chironomus species. Rempel's [100] description of C. hyperboreus from Saskatchewan was based on misidentification of a species later named C. rempelii [101].
Chironomus sp. 1TE may be an undescribed species close to C. saxatilis Wülker et al., 1981. The polytene chromosomes of a specimen with COI-barcode grouping with C. sp. 1TE in BIN BOLD:AAC0592 indicate that it cannot be C. saxatilis and do not match any cytologically studied species from the Holarctic (Jon Martin pers comm.). The species has halophilus-type larvae.

Sergentia
The species Sergentia coracina is listed as present on Svalbard in recent checklists [86,92,98]. The record seems to have originated from Edwards' [28,29] records from Bear Island, referring to "Lauterbornia ? coracina, Zett." and "Chironomus coracinus, Zett." respectively. Later sources report the species from Spitsbergen [47,101], but this was likely based on a misconception that Svalbard and Spitsbergen refer to the same land masses [29]. Edwards [31] further discussed the Bear Island records and described the previously recorded specimens as different from Zetterstedt's types of Chironomus coracinus. He named the species Chironomus psilopterus (see comments on Stictochironomus). We have not seen material of Sergentia coracina from Svalbard and do not know of reliable records. Based on the above discussion, we therefore regard the species to be absent from the archipelago but include Sergentia in the identification keys since it is not completely unlikely that it will be found there in the future.

Stictochironomus
Stictochironomus psilopterus (Edwards, 1935) was described as Chironomus psilopterus based on material from several lakes on Bear Island [31]. The species was later placed in Sergentia and also recorded from Lapland [47,101,102] but in recent checklists, the name has been regarded as a nomen dubium in Sergentia [103]. According to the original description, however, the species belongs to the genus Stictochironomus and we are confident that we collected this exact species as males and larvae on Bear Island ( Figure 20). The species appears similar to S. sticticus (Fabricius, 1781) and S. unguiculatus (Malloch, 1934) in the adult male, but can be separated by more than 10% divergence in DNA barcodes. We DNA-barcoded several additional, likely undescribed species of Stictochironomus from other regions, and a taxonomic revision of the genus is needed to identify morphologically diagnostic features of all species. Bista et al. [104] recorded and DNA barcoded specimens identified as "Sergentia psiloptera" from the UK (GenBank accessions KY225371, KY225372), but this appears to be an erroneous identification that matches our Sergentia sp. TE2 from mainland Norway.

Allocladius
The species we call Allocladius sp. 1ES seems to be close to Allocladius nanseni (Kieffer, 1926), but is separated from the latter by >6% uncorrected genetic distance. Morphologically, it is difficult to separate the species from A. nanseni, A. aizaiensis Wang, 1990 and A. arenarius (Strenzke, 1960) as described by Ferrington and Saether [48]. We collected one female and several larvae of this species, which is the first record of Allocladius from Svalbard. DNA barcodes in BOLD match those of specimens from Arctic Canada and Greenland.

Bryophaenocladius
We collected and barcoded females of one Bryophaenocladius species from Spitsbergen but are unable to associate them with a known species. Our species is therefore assigned the interim name Bryophaenocladius sp. 5ES. The DNA barcode match that of a specimen collected on Iceland, but otherwise there are no matching records in BOLD at present.
We also examined a male Bryophaenocladius from Spitsbergen collected by Brigitte Lods-Crozet near Ny Ålesund. It is not possible for us to associate this male with the above-mentioned female, nor to any described species. It is rather similar to Bryophaenocladius saanae Tuiskunen, 1986, but has a considerably higher antennal ratio (AR 1.75 vs. AR 1.25 in B. saanae).

Camptocladius
Recent listings of the species Camptocladius stercorarius from Spitsbergen [3,86] seem to originate from Holmgren's [26] report of material from "Green Harbour", "Advent Bay", "Nordkap" and "Storfjorden" under the junior synonym of Chironomus byssinus (Schrank, 1803). We examined males and females from Holmgren's Spitsbergen material of C. byssinus deposited in the Swedish Museum of Natural History in Stockholm. Unfortunately, the seven specimens were considerably damaged in the mail, to the extent that some broken off parts were impossible to assign to any labelled individual. However, it is clear that at least the two examined male specimens do not belong to Camptocladius stercorarius but to Smittia extrema Holmgren, 1869. Thus, we regard C. stercorarius to be absent from Svalbard, agreeing with the conclusion reached by Edwards [29].

Chaetocladius
Chaetocladius perennis has been reported from Svalbard by several authors, e.g., [92]. However, the DNA barcodes of Chaetocladius specimens morphologically fitting previous descriptions of C. perennis from Svalbard are very divergent from the barcodes in continental populations of this species. Closer examination of our Svalbard specimens reveals that these have dark brown halteres (in macerated individuals) as opposed to the pale or yellowish halteres described by Meigen [105] and later by Edwards [106] based on specimens from Germany and Great Britain, respectively. Unpublished notes by Edwards confirm that he had examined presumed type specimens of Meigen before writing his key to British Chironomidae (M. Spies pers. comm. 05.ix.2016). BOLD holds DNA barcode data of specimens from continental Norway, Greenland and Canada that belong to a single BIN (BOLD:AAC8747). We have seen specimens from Central Norway belonging to the «true» C. perennis cluster that fit the original description, and there are DNA barcodes of specimens from Germany and southern Canada in the same BIN (BOLD:ACF6903). We have not seen specimens from Svalbard or other Arctic regions that fit Meigen's (1830) or Edwards' (1929) description of C. perennis. Moreover, the larvae associated with the Svalbard population through DNA barcodes differ markedly from described Chaetocladius larvae in having a premandible with three strong teeth of which the apical one is serrated ( Figure 24n); see the genus diagnosis in Andersen, et al. [84]). Saether [57] examined two syntypes of Camptocladius incertus Lundström, 1915 from Siberia and synonymized this name with Chaetocladius perennis (Meigen, 1830) mainly based on male hypopygial features. Saether did not describe the halteres of the examined types, but the original description states that the species has black halteres [107]. Thus, we regard the Svalbard population to be Chaetocladius incertus (Lundström, 1915) and Saether's synonymy as incorrect.
A third species of Chaetocladius present on Svalbard is morphologically very similar to C. incertus, but separated from the latter by >7% uncorrected genetic distance. We only examined one specimen from Spitsbergen (male, specimen ID SV91), but it seems to be slightly different from C. incertus in having an evenly broad (parallel-sided) gonostylus ( Figure 24f). More specimens are needed to describe this possibly new species properly. Thus, a temporary name Chaetocladius sp. 8ES is assigned to this specimen in BOLD. We have also seen two Chaetocladius specimens from Jan Mayen that are similar to Chaetocladius sp. 8ES, but due to the condition of these slide mounted specimens we cannot evaluate wether or not they are conspecifiC. They have no associated DNA barcodes.
Chaetocladius dentiforceps, C. dissipatus, C. laminatus and C. piger (Goetghebuer, 1913) have been reported from Svalbard in ecological studies [88,108], but in low numbers. Chaetocladius dentiforceps, C. laminatus and C. piger were only recorded as immatures and these records must be regarded as doubtful. Moreover, the re-examination of a pupa from this material previously determinated as C. laminatus showed that it likely belongs to C. holmgreni (Jacobson, 1898) instead. Re-examination of adult males from Lods-Crozet's material determined as Chaetocladius dissipatus and C. suecicus revealed that these are morphologically consistent with what is currently regarded as C. holmgreni and C. incertus respectively. In summary, we consider three Chaetocladius species as recorded from Svalbard with certenty, C. holmgreni, C. incertus and C. sp. 8ES.

Corynoneura
The genus Corynoneura is represented on Svalbard by one form that might be a parthenogenetic population of Corynoneura arctica Kieffer, 1923. We are, however, not able to assign the examined females to C. arctica based on morphology, and DNA barcodes from the Svalbard population in BOLD belonging to a BIN (BOLD:ABZ8189) separated from its nearest neighbour (containing specimens identified as C. arctica) by at least 1.58% uncorrected genetic distance. The BIN containing the Svalbard specimens also includes representatives from throughout northern Canada, one from Central Norway, and one from Alaska. Our record of Corynoneura sp. 1ES is the first contemporary record of the genus from Svalbard, but subfossil material identified as the Corynoneura arctica type has been recorded from Spitsbergen (referred to as C. scutellate type) [109].

Cricotopus
Cricotopus is one of the most widely distributed and species rich genera in the subfamily Orthocladiinae. It appears to be particularly diverse in the Holarctic region and has numerous species in the ArctiC. Six species are recorded from Svalbard with certainty (see key below). In addition, Cricotopus (Cricotopus) polaris was reported by Lods-Crozet, et al. [88] and Marziali, et al. [108]. Based on examination of material kindly sent by B. Lods-Crozet, the specimens belong more likely to Cricotopus (C.) tibialis (Meigen, 1804). Cricotopus (Cricotopus) humeralis with its junior synonym Cricotopus (Cricotopus) ephippium (Zetterstedt, 1838) was recorded from northern Spitsbergen by Edwards [29], as a C. humeralis. However, according to Hirvenoja [50], page140, Edwards misinterpreted the species C. tibialis. We have not seen material of C. (C.) humeralis (or ephippium) from Svalbard. Heterotrissocladius subpilosus (Kieffer, 1911) was described by Kieffer in Koenig ( [71]: p. 273) from Bear Island as Dactylocladius subpilosus. We have examined material collected on Bear Island identified by Edwards [31] and can confirm that this material is conspecific with current understanding of H. subpilosus as described by Brundin [110] with a strongly swollen clypeus in the adult male. Photos and DNA barcodes of the H. subpilosus presented here are from specimens collected in Central Norway.

Hydrosmittia
The genus Hydrosmittia currently has one nominal species recorded from Svalbard, but DNA barcode data indicate that there is an additional un-clarified species present. Of both species, only females were collected.
Hydrosmittia oxoniana (Edwards, 1922) (Figure 34c-e,g) was originally described as Camptocladius oxonianus based on females from Bear Island. Hirvenoja [33] reported females from Spitsbergen. Later records include males and indicate a wide distribution throughout the Holarctic [48]. We have only recorded females from Bear Island and Spitsbergen and DNA barcodes of these specimens constitute a well-separated cluster compared to other Hydrosmittia from Svalbard and mainland Norway, including a male H. oxoniana from Central Norway identified by Ole A. Saether. The species is listed with a total of 9 junior synonyms [48]. Thus, we suspect that there are several unrecognized species currently hidden within H. oxoniana sensu Ferrington and Saether (2011), but that our sampled populations from Bear Island (locus typicus) and Spitsbergen belong to the nominal species.
Hydrosmittia ruttneri occurs on Spitsbergen according to Ferrington and Saether [48], but we have been unable to verify the source of this record and have never seen material of this species from Svalbard. The record might have been kept by a lapsus following the authors' interpretation of Edwards' [111] identification of Smittia oxoniana from Lapland. Edwards had considered the latter as conspecific with his specimens of the same species from Spitsbergen but Ferrington and Saether [48] explicitly disagreed and stated that the specimens Edwards had identified from Lapland do not belong to the same species as those from Spitsbergen. We regard H. ruttneri as absent from Svalbard.
Hydrosmittia sp. 1ES (Figure 34a,b,f) is morphologically similar to H. oxoniana, but DNA barcodes constitutes a genetic cluster that is clearly divergent from those of the latter species. We suspect that the specimens represent a second species, but morphological confirmation including comparison with type material for the many synonyms of H. oxoniana is needed to be certain.

Limnophyes
The genus Limnophyes has four confirmed species on Svalbard (see key below). An additional species, Limnophyes edwardsi, has been recorded from ecological studies in Ny Ålesund by Lods-Crozet, et al. [88] and Marziali, et al. [108]. Revision of this material kindly sent by B. Lods-Crozet showed that the specimens fit the description of L. brachytomus in Saether [55] and that Saether, who had identified the specimens, wrote "? edwardsi" on the slides. Saether [55] also listed Spitsbergen as part of the distribution range for L. edwardsi, but there are no records of specimens in his long list of examined material and no references to relevant literature. Saether [55] refered to Edwards' [106] interpretation of L. pumilio, but only listed Edwards' material from Scotland as examined. We therefore regard L. edwardsi not to be present in Svalbard. Limnophyes pumilio (Holmgren, 1869) was described based on material from Spitsbergen collected at Green Harbour, Advent Bay and Smeerenberg ( [26]: p. 41). a DNA barcode cluster comprising specimens from Spitsbergen, Greenland, Arctic Canada and one specimen from Finnmark thus appears to present the true species. Additional specimens from mainland Norway, Greenland and Arctic Canada identified as L. pumilio in BOLD are found in three additional BINs with a maximum pairwise distance of 6.11% to the nearest neighbour. Nevertheless, we regard all these genetic clusters as members of the same species.
Limnophyes schnelli was first described from mountainous regions in central and western Norway [55]. We have DNA barcodes of females from Bear Island that cluster closely with male and female specimens from northern Norway (Finnmark), northern Finland and numerous localities throughout Canada (BIN BOLD:AAC9278). The species was previously known from several countries in the northern Palaearctic [86], but this is the first record of L. schnelli from Svalbard.

Metriocnemus
Five named and valid Metriocnemus species and one hitherto undescribed species have been recorded from Svalbard with certainty (see keys below). In addition, there are four previously recorded species names, which examination of reference material has revealed misidentifications: Chironomus callosus Becher, 1886 was described from Jan Mayen based on adult males and females [34]. The description is rather good for its age, including details such as an enlarged clypeus, which likely contributed to to some authors subsequentely placing the species in Heterotrissocladius [3]. Edwards [35] examined the type series and noted that all Becher's specimens were freshly emerged once the colouration of which had then faded in ethanol. He thus considered only conspecific specimens collected on Jan Mayen by W. S. Bristow in 1921 to show the true, uniformly dull black colour. The observation of a few setae on the tip of the wing (in cell r 4+5 ) indicated high similarity to Heterotrissocladius subpilosus, but Edwards [31] ruled out the latter species since the Becher species (as represented by Mr. Barstow's specimens) has a produced costa similar to what is observed in Metriocnemus. Consequently, Edwards regarded C. callosus as a Metriocnemus. We have examined Becher's types (one male and three females) on loan from Naturhistorisches Museum Wien and agree with Edwards' conclusions. The specimens, though damaged, conform well to the current definition of Metriocnemus ursinus and we therefore regard C. callosus as a junior synonym.
Metriocnemus similis was listed from Svalbard in Lindegaard [98], likely based on the record by Hirvenoja [33]. The species was originally described from Novaya Zemlya [113]. We have examined the holotype deposited in NHM Oslo and regard the name as a junior synonym of Metriocnemus ursinus. It does not belong to Heterotrissocladius as was suggested by Ashe and O'Connor ( [3]: p. 311). We were able to extract DNA from the holotype and obtain a short COI-sequence of 103 base pairs. The mini-barcode matches our Metriocnemus ursinus specimens from Svalbard by 99.02%.
The only record of Metriocnemus tristellus from Svalbard known to uswas published by Goetghebuer [112] from the island of Hopen. The antennae are missing from the examined male (NHM Oslo), but the general morphology and hypopygium fits Metriocnemus sp. 1ES, not M. tristellus as described originally by Edwards [106] and subsequently by Langton and Pinder [114] where the palpi were reported to be unusually short, with palpomeres 3 and 4 less than three times as long as broad and with the anal point rather long and slender [114]: Figure 168B. Thus, we regard the previous presence of M. tristellus in the list of Svalbard Chironomidae as erroneous due to misidentification.

Metriocnemus brusti
Metriocnemus brusti was originally described from Churchill, Manitoba and has been recorded in the eastern Palaearctic, Novaya Zemlya and Switzerland in addition to the Nearctic region [86]. DNA barcodes from our specimens collected on Spitsbergen and Edge Island cluster nicely with those from the locus typicus as well as from Greenland, northern Norway and a number of other northern localities in Canada. Our specimens also fit well with the original description. Our records are the first of this species from Svalbard.
Metriocnemus cataractarum Kieffer, 1919 was described from Svalbard based on females, Oliver [51] reported males from Bear Island, but we regard this association as doubtful (see comment on Metriocnemus sp. 1ES below). Edwards [30] recorded doubtfully identified males from Reinsdyrsflya and Roosneset, north on Spitsbergen. Thus, certainly associated males of this species are unknown to us. We have DNA barcoded Metriocnemus larvae from Spitsbergen (Metriocnemus sp. 8ES, see below) with no related sequences from adult specimens in BOLD. These might represent M. cataractarum or a hitherto unknown species from Svalbard.
Metriocnemus eurynotus (Holmgren, 1883) was originally described from Vaygach Island south of Novaya Zemlya and has been regarded as a widely distributed species [54,56] (sub M. obscuripes in Saether [54]). Our DNA barcode data from the Palaearctic region form five defined barcode clusters and indicate several cryptic species in this group. This is perhaps not surprising given the list of currently held junior synonyms [54,56]. All specimens from Svalbard fall within the same genetic barcode cluster.
Metriocnemus fuscipes is considered widespread in the Holarctic Region, but was previously unreported from Svalbard [86,92]. Goetghebuer [112] recorded the species from eastern Greenland. Our specimens from Spitsbergen and Bear Island clusters with specimens from mainland Norway and south of Bonn in Germany (close to locus typicus for the nominotypical species) (BIN BOLD:AAI1573). Additional DNA barcodes from other populations in Norway and the German Alps form an additional three clusters that are genetically deeply divergent from this group.
Metriocnemus sp. 1ES differs from other described Metriocnemus species by having males with a combination of reduced wing setation, few temporal setae on the head, AR between 1.8-2.2 and a slightly broader and blunt anal point. The species seems to be quite similar to Oliver's [51] interpretation of M. cataractarum Kieffer, 1919. However, the latter was based on females only and our DNA barcode associated females of M. sp. 1ES do not fit Kieffer's description [27] as they have quite differently structured antennae with shorter flagellomeres (Figure 43e).
Metriocnemus sp. 8ES ( Figure 44) was collected only as larvae from northern Spitsbergen. The species belongs to the eurynotus group [84], but we have been unable to match it with any other species present in BOLD. There are two Metriocnemus species of the eurynotus group that have Arctic distribution but are unrepresented in BOLD. Metriocnemus longipennis (Holmgren, 1883), a peculiar species with reduced wings, antennae and thorax, was described from Novaya Zemlya and later recorded and redescribed from New Siberia [56,57,107] and northernmost Alaska [54]. Metriocnemus sibiricus (Lundström, 1915) was described from the New Siberian Islands and redescribed by Saether [54]. The male of the latter species resembles M. longipennis in its shortened wings and reduced antennal plume, but differs by the shape of the gonostylus, by normal wing setation and the higher number of flagellomeres.

Orthocladius
Orthocladius is represented by eight nominal valid species in Svalbard. In addition, we have material of one species that is putatively new to science. Four of the presently six subgenera have been recorded.
Orthocladius (Eudactylocladius) gelidus was first recorded by Hirvenoja [33] from Helvetiafjellet on Spitsbergen. The material could not be located at the Finnish Museum of Natural History in Helsinki. Given that later taxonomic papers have both, revised definitions in the genus and added species to the fauna of Svalbard [58,59,115], we regard the record in Hirvenoja [33] as doubtful. The species was later recorded from the stream Londonelva near Ny-Ålesund on Spitsbergen [88]. We have examined an adult male from this material kindly sent to us by B. Lods-Crozet and find it to be conspecific with our material of O. (E.) gelidorum from Svalbard as well as with the redescription of the latter species by Cranston [115]. We thus regard O. (E.) gelidus as hitherto undocumented from Svalbard.
Orthocladius (Euorthocladius) thienemanni has been reported in an ecological study from Ny Ålesund [88,108], but re-examination of a pupal skin from this material kindly sent to us by B. Lods-Crozet showed that it fits our associated pupae of Orthocladius (Euorthocladius) telochaetus Langton, 1985 (associated here for the first time). We thus regard the previous record of O. (Euorthocladius) thienemanni in Svalbard to be a misidentification.
Orthocladius (Orthocladius) rhyacobius was originally described based on material collected by Thienemann in Germany [119]. It was regarded as a distinct species by Rossaro, et al. [117], but their taxonomic treatment of this and associated species was questioned by Spies and Saether [118]. The species was recorded as adult males by Lods-Crozet, et al. [88] from Bayelva near Ny-Ålesund on Spitsbergen. We have examined two poorly preserved specimens from this material and find them conspecific with O. Orthocladius (Orthocladius) trigonolabis Edwards, 1924 was originally described from northern Spitsbergen [29] and the name is frequently seen in faunistic literature on Svalbard. Saether [57] found this name to be a junior synonym of O. (O.) nitidoscutellatus Lundström, 1915 (originally described from northern Russia) and later described larvae of this species from Svalbard [59]. Orthocladius (Eudactylocladius) almskari was originally described as O. (Eudactylocladius) schnelli Saether, 2004 from Lake Birgervatnet in north-western Spitsbergen [58]. Due to junior homonymy, Saether in Spies and Saether [118] renamed the species to O. (Eudactylocladius) almskari. The three species of Eudactylocladius from Svalbard are very similar in the adult male and can only be separated by minor differences in the hypopygium and the tarsal sensilla chaetica. Orthocladius (Eudactylocladius) sp. 2TE cannot be assigned to any scientifically named species and is given an interim name until more material will allow formal description. In BOLD, there are two specimens of the same BIN from Northwest Territories and Yukon (Canada), indicating that O. (Eudactylocladius) sp. 2TE is an arctic species.
Orthocladius (Eudactylocladius) sp. 2TE has been recorded from Svalbard as single female from Bear Island. However, the DNA barcode of this specimen groups with a male from Finnmark, northern Norway and enables us to separate the species from other Orthocladius recorded from Svalbard. The male adult keys to Orthocladius (Eudactylocladius) sublettorum in [58], but differs by having slightly more setae on the squama and no crista dorsalis. The DNA barcodes of O. (Eudactylocladius) sp. 2TE are more than 8% divergent from those in BOLD identified as O. (Eudactylocladius) subletteorum from North America, Central and northern Norway.
Orthocladius (Euorthocladius) telochaetus Langton, 1985 was described based on two original syntypes of Chironomus limbatellus Holmgren, 1869 that were not conspecific with the syntype selected as lectotype for Psectrocladius limbatellus (Holmgren) [63]. DNA barcodes of Orthocladius (Euorthocladius) telochaetus from Svalbard cluster tightly with barcodes from Orthocladius (Euorthocladius) rivicola Kieffer, 1911 from mainland Norway. Soponis [61] diagnosed adult males of Orthocladius (Euorthocladius) telochaetus by the apical seta on the anal point. We have observed specimens without this feature and also with an anal point much shorter than in the type series (Figure 48e,f). However, the very low dorsal lobe of the inferior volsella and the darker colour of the specimens seem to be good characters to separate male adults of O. (Euorthocladius) rivicola reported as larvae in an ecological study near New Ålesund (Spitsbergen) by Blaen, et al. [120] as misidentifications due to the difficulty of separating species in Eurorthocladius in the larval stage [61], and to the fact that the larva of O. (Euorthocladius) telochaetus has been unknown.
We have not seen material of Orthocladius (Orthocladius) knuthi Soponis, 1977 from Svalbard, but Soponis [72] based her original description partly on a male (paratype) from Hornsund (Spitsbergen). (O.) knuthi should be regarded as uncertain due to few examined specimens and the brief original description [72].
Orthocladius (Orthocladius) mixtus (Holmgren, 1869) was originally described from Bear Island based on a female adult [26]. Edwards [29] reported males from northern Spitsbergen and regarded the name as a senior synonym of Orthocladius arcticus Kieffer, 1919, despite differences in body colour [27,29,113]. Edwards [31] recorded two males from Bear Island with questionable identification to O. mixtus. We have compared our female specimens with photographs of the genitalia and critical mensural data of the holotype and find this material to be conspecifiC. Consequently, we can confirm the placement of Orthocladius mixtus (Holmgren) in the subgenus Orthocladius as suggested by Cranston [115]. Previously, the species name has been treated as a junior synonym of Orthocladius (O.) decoratus (Holmgren, 1869), and most recently as a nomen dubium in the subgenus Orthocladius [3]. We now regard it as denoting a separately valid, well defined species. The latter is very similar to the male, female and pupa to Orthocladius (O.) wiensi Saether, 1969 [72,121], but differs in being larger (male standard wing length approx. 2.5 mm), having a lower adult male AR (1.2), more setae on the male laterosternite IX and by having fewer spinules on TIII and TVI of the pupal abdomen. DNA barcodes of our Svalbard specimens cluster tightly with specimens from the northwestern Yukon in Canada (BIN BOLD:AAE4991).

Paralimnophyes
The genus Paralimnophyes has been recorded from Spitsbergen only once as a single larval head capsule, sampled with a battery-driven pooter in a kittiwake nest [85]. We have examined the specimen and find that this likely belongs to Limnophyes as there are only three well developed inner teeth on the mandible. We thus consider the record of Paralimnophyes on Svalbard as doubtful. The genus is nevertheless included in the above key for future reference. The larva is known for only one European species, and the latter is not the candidate most likely to occure on Svalbard, Paralimnophyes trilineatus (Lundström, 1915).

Paraphaenocladius
Paraphaenocladius impensus was recorded from Spitsbergen by Hirvenoja [33]. The record went undetected by Saether and Wang [122], who did not see material from Svalbard for their revision of the genus. We have examined the specimens on which Hirvenoja's recordwas based and find that these belong to Paraphaenocladius brevinervis (Holmgren, 1869).

Psectrocladius
The genus Psectrocladius is represented with five species on Svalbard. We have seen material of and DNA barcoded P. (Monopsectrocladius) calcaratus, P. (Psectrocladius) octomaculatus, P. (P.) psilopterus, P. (P.) barbimanus, P. (P.) limbatellus and P (P.) oxyura, but only the material of the latter three species was from Svalbard. Therefore, several of the diagnostic characters in the key below are retrieved from literature, in particular from [62,63,123,124].
Psectrocladius (Monopsectrocladius) calcaratus (Edwards, 1929) was reported by Langton [63] based on one male adult in Edwards' material from Spitsbergen. We have examined this specimen and find it to belong to P. (P.) limbatellus. Since this was the only known record of P. (M.) calcaratus from Svalbard, we now regard this species to be absent from the archipelago. We have nevertheless included it in the below key and figures to avoid future confusion. Our understanding of this species is based on literature and DNA barcoded specimens from northern and central Norway (counties Finnmark and Trøndelag).
Psectrocladius (Psectrocladius) psilopterus was recorded from Spitsbergen by Lods-Crozet et al. [88]. We have examined a male adult from this study and can confirm the similarity with Psectrocladius Insects 2020, 11, 183 30 of 103 (P.) psilopterus. However, there are slight differences in both colouration and hypopygial structures in a barcoded specimen of P. psilopterus from southern Norway that matches DNA barcodes of this species from Finland. The specimen we had on loan was unfortunately damaged in the return mail to the museum in Trento, Italy, but photos were taken before this shipment (available upon request). We consider P. psilopterus as absent from Svalbard, and regard the specimen recorded by Lods-Crozet, et al. [88] as belonging to a separate species (see Psectrocladius (P.) borealis below).
The species Psectrocladius (Psectrocladius) ventricosus has been included in checklists from Svalbard [93,98]. The record likely originates from Hirvenoja (1967) who reported the species from Lindholmhøgda in Adventdalen (Spitsbergen). Immature stages of Psectrocladius (P.) ventricosus have been recorded mostly from brackish or very hard water [62,123]; thus, it may be considered as unlikely to occur in the streams or ponds near Lindholmhøgda. Not all of Hirvenoja's specimens could be located, but we have examined two males and these fit the diagnosis of P (P.) limbatellus except for having an antennal ratio of 2.2. The fact that Hirvenoja [33] reported P. (P.) limbatellus pupal exuviae (but no adults) from the nearby Isdammen, and that we have collected adult specimens of this species in the closely located Gruvedalen and Todalen, support our interpretation that the record of P. (P.) ventricosus was likely based on a misidentification. We therefore regard P.

Preliminary Key to FeMales
This key is based on keys by Langton [63] and Saether and Langton [124]. We have only seen females of P (P.) barbimanus, P. (P.) limbatellus and P. (P.) oxyura, thus could not test whether all characters used below will work on specimens from Svalbard. Additional characters that might be useful to separate females in Psectrocladius include the sizes and shapes of antennal flagellomeres as well as the pigmentation pattern on abdominal sternite VIII. The species Psectrocladius (Psectrocladius) cf. borealis Kieffer, 1919 was originally described from Spitsbergen in Kieffer and Thienemann [27] and later recorded by Edwards [28,29]. We have examined two adult male specimens from Edwards' material that fit the (limited) original description by Kieffer ( Figure 56), but given the observed morphological variability in P. (P.) limbatellus (see below), we cannot say with certainty if P. (P.) borealis constitute a separate species. We nevertheless choose to include the species as a separate entity in the key and figures. Material of Psectrocladius (P.) psilopterus recorded by Lods-Crozet et al. [88] from a Malaise trap near Bayelva on Spitsbergen (see comment above) apparently is conspecific with Edwards' material of Psectrocladius (P.) borealis. The species is similar to Psectrocladius (P.) psilopterus and the related P. (P.) bisetus Goetghebuer, 1942 and P. (P.) simulans Johannsen, 1937, but is darker in colour and has a straight posterior margin of the inferior volsella. DNA barcodes from the Spitsbergen population are unavailable.
Psectrocladius (Psectrocladius) limbatellus (Holmgren, 1869) was originally described from Spitsbergen, but records have been reported from many countries in Europe, the Nearctic, the Near East and North Africa [86]. We have DNA barcodes from the Spitsbergen population that match those of specimens from Greenland and northern Canada (Churchill). Some of the matching specimens in BOLD from Greenland are currently identified as P. (P.) barbimanus and P. (P.) sokolovae, respectively (det. L. Paasivirta). Genetically divergent populations (>4% K2P distance) that are morphologically very similar to P. (P.) limbatellus have also been examined by us. These specimens are from northern Canada, central and northern Norway. Thus, we suspect that there currently are more than one species hiding under the name P (P.) limbatellus and that the nominal species has a narrower geographical distribution than present records indicate. At the same time there appears to be considerable morphological variation in the adult male hypopygia among specimens belonging to the same barcode cluster (Figure 57f,g). Thus, a revision including genetic characters is needed in order to clearly separate the closely related species of the limbatellus group. The females of the Spitsbergen population are larger than what has been described from England (also noted by Langton [63]) and more similar to P. (P.) barbimanus than previous identification keys indicate [63,124]. Thus, additional characters are introduced in the key above to accommodate differences observed in Spitsbergen material of both species.
Psectrocladius (Psectrocladius) octomaculatus Wülker, 1956 was reported by Langton [63] to be present in Edward's material from Spitsbergen. We have seen the specimen examined by Langton and agree with the interpretation.
Psectrocladius (Psectrocladius) oxyura Langton, 1985 was described based on material from Cow Green Reservoir, England [63], but a wider distribution is indicated in the original description since at least part of the material identified as P. (P.) limbatellus by Brundin [47] and Wülker [62] fits the diagnosis of P. (P.) oxyura. We have examined and DNA barcoded populations from Bear Island and Spitsbergen that group with specimens from Canada and Greenland in BOLD.

Smittia
Based on our review of the literature and available specimens (see below), the genus Smittia has three formally named species recorded from Svalbard. However, DNA barcode data indicate at least ten species from the archipelago and an additional two from Jan Mayen. Of these twelve species, ten are so far known as females only and we suspect that at least some of them are parthenogenetiC. Most of the species can be separated by morphology and are keyed to species below. We have seen associated larvae of four of the seven unnamed species; in addition, we have associated larvae of S. brevipennis (Boheman, 1866), S. extrema (Holmgren, 1869) and S. longicosta (Edwards, 1922). We prefer to use interim names for species that we cannot assign to described and formally named taxa. Some of them might be facultative parthenogenetic with a wider distribution, and some might already be described as males. Thus, even before certain associations are made, we release the DNA barcodes and describe selected morphological characteristics to make the material available for future revisions.
Smittia flexinervis was described as adult male in Thrichocladius [sic!] from Bear Island [71]. We have not been able to locate the type material of this species and the latter cannot be identified or associated with recent material from the original description only. Camptocladius longicosta Edwards, 1922 was described from Bear Island based on 14 females [28]. The name is listed as a synonym of Smittia flexinervis, but it is not clear who originally suggested this synonymy [3,86]. It could have originated from Edwards' (1922: p. 201) rather vague statement in the original description: "It is just possible that it may be the female of C. flexinervis, Kieff." Given the high diversity of Smittia in the archipelago, this association is far from certain and we therefore regard S. flexinervis as a nomen dubium (see additional comment on S. longicosta below).
Smittia spitzbergensis (Kieffer, 1911) was described in Thrichocladius [sic!] based on a female from Hornsund, Spitsbergen [71]. From the drawing of the antenna, it clearly belongs to Smittia, but we are unable to associate the description with any of the morphotypes we have examined from the archipelago. The most similar species with regard to the antenna might be our Smittia sp. 7ES, but females of this species are considerably lighter in colour and have a shorter 5 th flagellomere and a shorter 5 th palpomere. We regard S. spitzbergensis as a nomen dubium until specimens can be associated with the original description and provide a better understanding of this species.
Smittia lasiophthalma was first described from Dubois, Illinois (USA) based on a female adult [125]. The record from Jan Mayen referred to in the World Catalogue [3] and Fauna Europaea [86] probably originates from Edwards' questionable identification of Bristow's material [35]. Edwards [30] also recorded this species with an uncertain identification from northern Spitsbergen (probably Reinsdyrflya). We have not compared Malloch's types with Edwards' material, but have examined a specimen from Edwards' material in NHM labelled Smittia cf. lasiophthalma. This is conspecific with Smittia sp. 25ES discussed below. In light of the present knowledge of Smittia diversity in the Arctic, we regard it as unlikely that Smittia lasiophthalma is present on Svalbard and Jan Mayen.
Smittia lasiops was originally described in Camptocladius based on males and females collected near a house in Urbana, Illinois (USA) [125]. a female from the North Cape at Nordaustlandet on Svalbard was identified with some uncertainty by Edwards [29], which is likely the source for the species' record for Svalbard in Lindegaard [98], Fauna Europaea [86] and the World Catalogue [3]. We regard the presence of S. lasiops on Svalbard as doubtful.
Trichocladius polaris Kieffer, 1919 has a type locality on Spitsbergen and is regarded as a subjective synonym of Smittia extrema (Holmgren, 1869) [3], likely based on Edwards' (1924) observations: "I had wrongly identified this species. Holmgren's specimens (16 ♀from North Cape, but no ♂) are all quite evidently the species I recorded as C. curvinervis, Kieff.; if the determination was correct, Holmgren's name will take precedence over Kieffer's curvinervis and over Becher's incertus, which has also proved to be the same species. Holmgren's specimens have black halters, not yellow as in Becher's and Kieffer's material." The observed differences in the colouration of the halters (described as white in the original description of Trichocladius curvinervis var. polaris) as well as differences in the female antenna (see Figure 7 in Kieffer and Thienemann [27]) indicate that these two species names are not synonyms. Moreover, the figured antenna does not show the subapical setae typical for Smittia [27]. The reminder of the description fits the diagnosis of Smittia, however. Thus, we regard T. curvinervis var. polaris as a nomen dubium probably in Smittia. The species should not be confused with Smittia polaris (Kieffer, 1926) revisited by Saether, et al. [126] from Greenland and northern Canada (Northwest Territories, Ellesmere Island). This species was originally described from Ellesmere Island [126,127]; records from Svalbard, Jan Mayen and Novaya Zemlya in Fauna Europaea [86] are of unknown origin and might be due to a mix-up of names.  10. Palpomere 4 less than three times as long as broad, palpomere 5 less than four times as long as broad; seminal capsule longer than 1 2 length of segment VII (Figure 69c) Smittia sp. 27ES -Palpomere 4 more than three times as long as broad, palpomere 5 at least five times as long as broad; seminal capsule shorter than 1 2 length of segment VII (Figures 61c and 68c Smittia brevipennis (Boheman, 1856: p. 575) was originally described as Chironomus brevipennis from Kvalpynten on Edgeøya [25]. We have examined and DNA barcoded specimens from Russebukta (close to the locus typicus) as well as from other localities on Edgeøya and Spitsbergen and have associated larvae (Figure 59f-i) with the characteristic, brachypterous females. Saether [57] redescribed the female genitalia of this species based on specimens from Siberia belonging to the Lundström collection.
Smittia extrema (Holmgren, 1869), originally described in both sexes from Nordaustlandet and Edgeøya [26], apparently has a wide Arctic distribution with records from Svalbard, Greenland, Canada and Russia [3]. DNA barcodes of the Svalbard population clusters with those of specimens from Zackenberg (Greenland), Nunavut and Northwest Territories. It is the only Smittia species from Svalbard with a recorded adult male as Smittia sp. 25ES has been found only on Jan Mayen, Greenland and in Canada. Chironomus incertus Becher, 1886 was originally described from Jan Mayen [34] and is listed as a questionable synonym of Smittia extrema in the World Catalogue of Chironomidae [3]. We have not examined the types (presumably in the Natural History Museum of Vienna), but based on Edwards' observations [35], we agree that the species should be placed in Smittia. However, in light of the presence knowledge of the Smittia diversity on Svalbard and Jan Mayen, it is not clear whether S. incerta is conspecific with S. extrema or with Smittia sp. 25ES or with yet another established Smittia species. Nor do we know if males were included in the original description. We therefore regard S. incerta as a nomen dubium in Smittia.
The species Smittia longicosta (Edwards, 1922) was first described based on adult females from Walrus Bay on Bear Island [28]. We have examined one of Edwards' syntypes and compared it with modern samples from the same area. We were also able to retrieve a 70bp mini barcode from the syntype that exclusively matches 100% with other barcoded specimens of S. longicosta from Svalbard. The species is identical to the one that [128] recorded under the interim name Smittia sp. 1ES. It is quite similar to what we call Smittia sp. 26ES, but the antennal flagellomeres 2-4 are slightly more bottle-shaped in Smittia longicosta and the seminal capsule necks are more sclerotized in Smittia sp. 26ES. The two species separate well by DNA barcodes (>12% pairwise distance) and a specimen of S. longicosta collected only 1.5 km from the locus typicus has been barcoded. Smittia longicosta has records from Spitsbergen, Edgeøya and Bear Island, while Smittia sp. 26ES appears to have a wider distribution with records in BOLD from Canada (Alberta and Nunavut), East Greenland, Jan Mayen and Spitsbergen.
Smittia sp. 5ES and Smittia sp. 6ES are similar in several features, e.g., both have a wing membrane with coarse punctation. They can be separated by the characters in the key; in addition, it appears that females of Smittia sp. 6ES have more robust flagellomeres (Figure 65h). The short and broad sensilla trichoidea of the female antenna in Smittia sp. 6ES resembles those in Smittia aterrima (Meigen, 1818), but DNA barcodes of Smittia sp. 6ES are more than 8% divergent from those we have associated with males of S. aterrima from central and northern Norway. Smittia sp. 5ES is recorded from Spitsbergen and Bear Island, and DNA barcodes match those of specimens in BOLD from Newfoundland, Canada. Smittia sp. 6ES has records from Spitsbergen and Edgeøya with barcode matches from East Greenland and Nunavut, Canada.
Smittia sp. 7ES has been recorded from Jan Mayen, Spitsbergen and Bear Island. The species is relatively easily separable from other Smittia on Svalbard as its females are more slender with longer extremities than in the other Smittia.
The remaining Smittia species from Svalbard also seem to have a relatively broad arctic to sub-arctic distribution (based on BIN-matches in BOLD): Smittia sp. 27ES is recorded from Jan Mayen, Finland and Switzerland; Smittia sp. 2ES from Spitsbergen, Arctic Canada (Nunavut) and East Greenland; Smittia sp. 3ES from Spitsbergen, Finland and Canada (Yukon, Northwest Terretories, Nunavut, Newfoundland); Smittia sp. 25ES from Jan Mayen, East Greenland and Canada (Nunavut); and Smittia sp. 28ES from Edgeøya and Nunavut, Canada.

Tvetenia
Tvetenia bavarica has a wide distribution in the Holarctic Region and is here recorded from Svalbard for the first time. All specimens we have examined were from the warm springs Jotunkildene in Bockfjorden north on Spitsbergen, where we collected all major life stages ( Figure 71). The DNA barcodes of the Spitsbergen population cluster with DNA barcodes from mainland Norway, Finland, Germany and Georgia in BOLD (BIN BOLD:AAD2063), including specimens collected near the locus typicus in Bavaria, Germany.

Zalutschia
The species Zalutschia tatrica was listed as present on Svalbard by Lindegaard [98], but we have been unable to find the original documentation for this record. We have not seen any specimens of this species from the Archipelago either. In northern Europe, this species is recorded from northern Fennoscandia and the Kola Peninsula [53,129,130]. Until further documentation of this species becomes available, we regard it as not present on Svalbard and Jan Mayen (Figures 2-71).

Conclusions
Our review has confirmed that Svalbard has a surprisingly species-rich chironomid fauna. According to the records presented here, at least 74 species occur on Svalbard and Jan Mayen, with Spitsbergen as the most species-rich subregion (61 species). The high diversity on Spitsbergen compared to other regions in Svalbard (Table 1) almost certainly reflects that island's large landmass and larger diversity of habitats, but also the fact that this is by far the best investigated island of the archipelago.
There likely are additional species still to be discovered in Svalbard and Jan Mayen. We document 20 distinct forms that do not fit current diagnoses for established species and therefore are given interim names. Although several of these might be associated with named species in the future via taxonomic revisions and associations of life stages, we are convinced that some also represent species new to science.
Our review shows that a number of previous species records from Svalbard were erroneus. We believe this reflects the lack of suitable identification keys for the region, but also the high level of taxonomic experience needed to correctly identify chironomids to species using morphology. The use of identification keys that were designed for other geographical regions easily leads to errors. Since it is easier to introduce new names in a checklist than to get rid of erroneously introduced records, we urge scientists to confirm their identifications against original descriptions and taxonomic reviews before publication.
DNA barcode data has been extremely important for our work. In several cases, we could only detect morphological differences to closely related species after DNA barcodes indicated distinct genetic lineages (e.g., Orthocladius mixtus). DNA barcodes have also been fundamental to associate life stages, especially when larvae fit poorly into established generic diagnoses (e.g., Chaetocladius incertus). We believe that the genetic characterisation of communities using DNA barcodes should always be integrated in morphological studies of Chironomidae, especially when sampling little-known regions. Only then is it possible to archive good comparative understanding of the true diversity and of how it relates to the distribution of similar taxa in other regions.
Author Contributions: Both authors (E.S. and T.E.) contributed equally to conceptualization, methodology, analysis, writing and visualization. Both authors have read and agreed to the published version of the manuscript.
Funding: This research was in part funded by the Norwegian Biodiversity Information Centre through an inventory project on Svalbard's Diptera supported by the Norwegian Taxonomy Initiative (awarded to Geir Søli at the Natural History Museum, University of Oslo). DNA barcode data in this publication was generated in collaboration with the Norwegian Barcode of Life Network (NorBOL) funded by the Research Council of Norway and the Norwegian Biodiversity Information Centre. The APC was covered by the Norwegian University of Science and Technology (NTNU).