Checklist of terrestrial Parasitengona mites in Fennoscandia with new species- and distribution records (Acariformes: Prostigmata)

Abstract The knowledge of terrestrial Parasitengona in Fennoscandia lies far behind that of their aquatic counterparts, the water mites (Hydrachnidia). Based on new inventories, we provide primary data and an annotated checklist of terrestrial Parasitengona in Fennoscandia including 107 species. Out of these, nineteen species are new findings for the region and five are species potentially new for science. Twenty-three species are new for Norway, fourteen for Finland and eleven for Sweden. The known recorded fauna today of terrestrial Parasitengona is 80 species for Norway, 54 for Sweden and 48 for Finland. Primary data include georeferenced locality data as well as collecting techniques and microhabitat to increase the knowledge on species' habitat requirements.


Introduction
Parasitengona mites comprise two main ecological assemblages: the aquatic water mites (Hydrachnidia) and the terrestrial parasitengones (Trombidia; Figs 1,2,3,4,5,6,7,8,9). Together, the two groups form the monophyletic clade Parasitengona, characterised by their complex life cycle. Larvae of both aquatic and terrestrial lineages parasitise arthropods with few exceptions. The exceptions pertain to predatory or pollinivorous forms and the "chiggers", the vast majority of which have tetrapod vertebrates as hosts. The origin of water mites as either a sister group to, or being derived from within, terrestrial Parasitengona has been debated (Witte 1991, Welbourn 1991, but the latest evidence suggests a nested position of water mites (Dabert et al. 2016, Stålstedt 2017). There have been significant studies of water mites in Fennoscandia by Olov Lundblad, Sig Thor, Pauli Bagge and others (Thor 1897a, Thor 1897b, Thor 1899, Thor 1901, Lundblad 1927, Lundblad 1962, Lundblad 1968, Mehl 1979, Bagge and Bagge 2009, Stålstedt et al. 2013) and, at least in Sweden, the fauna is considered relatively well known. The terrestrial counterpart, Trombidia, however, has been largely ignored and the state of knowledge for the Fennoscandian fauna is very poor. However, in recent years the terrestrial parasitengones of Sogn og Fjordane in Norway (Mąkol and Gulvik 2002), as well as Finnish Erythraeoidea and Trombidiidae , Gabryś et al. 2009) have been studied. Several species known from larvae were recorded from Northern Europe by Haitlinger (2000) and Haitlinger (2008). In Sweden, there have been few studies in recent years.  summarised the current state of knowledge of multicellular life in Sweden and reported twelve species of Trombidia. This is without doubt a vast underestimate as, for example, 142 species are known from Poland (Mąkol and Wohltmann 2012, Moniuszko and Mąkol 2014, Stålstedt et al. 2016, Mąkol and Korniluk 2017, which is perhaps the best studied country in Europe. Therefore, we here present an updated checklist for Fennoscandia, based on new inventories. In the checklist, there are 107 species of terrestrial Parasitengona for Fennoscandia. Out of these, nineteen are new findings for the region and five are potential new species for science. In Norway, we present twenty species new for the country, plus three potentially undescribed species. In Sweden, there were nine species new for the country, plus two potentially undescribed species. In Finland, fourteen species were new findings for the country. This raises the known fauna to 80 species recorded for the Norwegian fauna, 54 for Sweden and 48 for Finland. In total, there are 499 records in the checklist, 383 of which are Norwegian. ecology and habitat requirements. Records are georeferenced with latitude and longitude coordinates in decimal degree format (WGS84) and altitude in metres, when available. Finnish collectors used a national uniform grid system (yhtenäiskoordinaatisto, YKJ) for mapping localities and this was converted into decimal degrees for the checklist. The locality records are downloadable as a csv file for easy creation of, for example, distribution maps with GIS tools. References to earlier records from Fennoscandia are provided in addition to new locality data. Taxa of uncertain identity (Trombiium russatum C.L. Koch, 1837, Trombidium procerum C.L. Koch, 1837, Trombidium hortense C.L. Koch, 1837, Trombidium corrugatum C.L. Koch, 1837, Trombidium assiratum C.L. Koch, 1837, Trombidium erythrellum C.L. Koch, 1837 and Rhyncholophus paludicola C.L. Koch, 1837), recorded by Andersén (1863) from Sweden, are not considered here due to their overall uncertain status followed by likely misidentifications. Each species is linked to the GBIF occurrence database. Under the distribution subheading, only the distribution in Fennoscandia is considered. Species, genus and family level taxonomy follows Mąkol and Wohltmann (2012) and Mąkol and Wohltmann (2013). The latter sources Wohltmann 2012, Mąkol andWohltmann 2013) also contain references to the original description of species, with the name in its original combination, author, date and page number of the description. Potential new species (or hitherto unknown instars) will be described elsewhere and are reported as "sp." here, with a note explaining the status. Species with only single occurrences in literature and without recent records in Fennoscandia are considered as questionable identifications.  (Trägårdh 1910, Sellnick 1958), Finland (Karppinen 1958, Gabryś et al. 2009) and new for Norway.
Notes: Only single record in literature (Thor 1900a) and no recent occurrences since then. Identification questionable.
Notes: Only single record in literature (Oudemans 1927) and no recent occurrences since then. Identification questionable.
Notes: Species described by Southcott (1992) from material collected by I. Trägårdh in 1907, in Sarek, Swedish Lappland.
Notes: Only single record in literature (Thor 1900a) and no recent occurrences since then. Identification questionable.
Notes: Only single record in literature (Berlese 1910) and no recent occurrences since then. Identification questionable.
Notes: Only single record in literature (Thor 1900) and no recent occurrences since then. Identification questionable.

Notes: Camerotrombidium sigthori Thor & Willmann, 1947 is a replacement name for
Ottonia purpurea s. Thor (1900b). Only single record in literature (Thor 1900b) and no recent occurrences since then. Identification questionable.
Notes: Only single record in literature (Thor 1900, as Ottonia vesiculosa) and no recent occurrences since then. Identification questionable.
Notes: Only single record in literature (Berlese 1910) and no recent occurrences since then. Identification questionable.
Notes: Only single record in literature (Thor 1900b, as Ottonia spinifera) and no recent occurrences since then. Identification questionable.
Notes: Only single record in literature (Thor 1900b, as Ottonia strandi) and no recent occurrences since then. Identification questionable.

Subfamily Trombidiinae Leach, 1815
make available and publish the primary data. There are many reasons for this: facilitate the re-use of biological data, facilitate integration with other datasets and increase the potential for interdisciplinary research, transparency and increased quality of science, citeability, credit and monitoring use of collection data ). This is becoming increasingly recognised by funding agencies and national governmental organisations in many countries.
The higher diversity, 80 species, for Norway is likely a result of the comparatively larger effort (71% of all visited localities were in Norway) and more recent studies (Mąkol and Gulvik 2002). The Norwegian non-marine arthropod fauna is commonly a smaller subset of the Swedish fauna, lacking more southern species occurring in Sweden. For some groups, however, Norway may instead house more oceanic or arctic species. Apart from collecting effort, the different number of species-level taxa, as well as species composition observed in Sweden, Finland and Norway, may also be due to biogeographical factors, landscape architecture and actual variety of biotopes. Solhøy et al. (1975) pointed to the decreasing tendency observed in the number of species along the gradient between the eastern and north-eastern territories of Finland, covered with continental tundra and towards alpine tundra influenced by Atlantic climate in Norway. Finland often also lacks some southern species occurring in Sweden, but instead may have eastern fauna elements not occurring in either Sweden or Norway. Even in Norway, the geographical area visited was quite limited, with most effort being spent in the county Sogn og Fjordane. Due to the intense collecting effort in different microhabitats, many species were recorded. Although the fauna is expected to be still more diverse due to the unsampled counties, the majority of species are only known from either larvae or active postlarval forms, which can contribute to some overestimations. Nevertheless, with the current classification, we predict that, if the same effort as in Norway was made in Sweden, over 80 species could be recorded in Sweden alone. The most frequent species was Calyptostoma velutinum (Müller, 1776), which was collected 70 times. The high number of observations occurring throughout the season may be due to the specific biology and phenology of Calyptostoma sp. reflected in synchronous occurrence of active life instars or it may reflect the occurrence of a species complex as suggested by Wohltmann et al. (1999). A DNA Barcoding effort of terrestrial Parasitengona mites could significantly help charting the diversity in Fennoscandia, reveal overlooked species or identify species complexes.
Special thanks to reviewers Dr. Bruce Halliday, Dr. Owen Seeman, Dr. Michael Skvarla and Dr. Andreas Wohltmann, who provided valuable comments that helped to improve the manuscript. JS and JB were supported by the Swedish Taxonomy Initiative (grant dha 154/09 1.4).