A synopsis of Estonian myriapod fauna (Myriapoda: Chilopoda, Diplopoda, Symphyla and Pauropoda)

Abstract The data on Estonian Myriapoda are scattered in various publications and there has been no overview of the fauna up to the present. A critical summary of the previous information on Estonian Myriapoda is given, supplemented by new records and distribution maps. Altogether, 5784 specimens from 276 collecting sites were studied. To the hitherto recorded 14 centipede species are added Lithobiusmelanops, L.microps, Geophiluscarpophagus, G.flavus, Strigamiatranssilvanica and Stenotaenialinearis, a probably introduced species. Of the 27 published Estonian millipede species, the data on two species proved erroneous, and two new species were recorded (Craspedosomaraulinsii and Cylindroiulusbritannicus). Two previously recorded millipede species – Brachyiuluspusillus and Mastigophorophyllonsaxonicum – were not found in the recent samples, the latter may have become more rare or extinct. Pauropoda and Symphyla lack previous reliable records. Combined with published data, the number of myriapod species known from Estonia is now set at 52. Some changes in species distribution and frequencies were detected comparing the published data with new records. Some data about habitat preferences of the more common species are also given. The majority of species have a western Palaearctic distribution, while six species are at the northern limit of their ranges.


Introduction
The research of Estonian Myriapoda has been quite unsystematic and sporadic. Very little has been published in English thus much of the information may be currently unavailable to the wider myriapodological community (e.g., Zapparoli 2003, Tuf et al. 2015. The first scant records of Myriapoda in Estonia date back to the second half of the XIX century. The first data are given by E. Haase (Haase 1886: 58), who mentions a "Craspedosoma mutabile v. fasciatum Latzel, 1884" specimen collected by A. E. Grube from Tartu. Subsequently, P. Schmidt reported the presence of Pauropus Huxleyi in the vicinity of Narva (Schmidt 1894) and O. Schubart published the data on two millipede species collected from Estonian bogs (Schubart 1924). W. Mierzeyewski collected in 1912 and 1926 some millipedes in the island Saaremaa, and in the years 1925 to 1929 W. Herold gathered a considerable millipede material from many places in Estonia. That material, containing 20 species, was also identified and published by O. Schubart (Schubart 1930), who repeated the data in his monograph on German Diplopoda (Schubart 1934). Part of the Herold material is currently preserved in the collection of Museum für Naturkunde, Berlin. In the 1930's, some ecological studies mention millipedes identified to genus level (e.g., Nõmmik 1939) and some species were listed in studies on plant pests (e.g., Zolk 1923, Kaarep et al. 1949). E. Palmén published one new record of Estonian diplopods in his overview of the Finnish fauna (Palmén 1949).
An unpublished collection of myriapods from 1937, preserved currently in the entomological collection of Estonian University of Life Sciences, Tartu (IZBE, identified by the Swedish zoologist H. Lohmander), has probably served as a basis to the list of ten centipede species in H. Riikoja's account of Estonian invertebrates (Riikoja 1955; referred to as pers. comm. with J. Vilbaste).
We owe thanks for much of what is known about Estonian Myriapoda to the works of the Estonian entomologist Juhan Vilbaste (1924Vilbaste ( -1985. His "Keys to Estonian Millipedes" lists 21 species as proven to occur in Estonia at that time (Vilbaste 1953). In addition, he published on Myriapoda in several local faunistic surveys, adding one centipede and five millipede species records and some ecological observations (Vilbaste 1970, Vilbaste 1979, Vilbaste et al. 1985, Vilbaste and Vilbaste 1993. Unfortunately, only two specimens of Vilbaste have subsisted (in the IZBE collection). The data provided by Schubart (1930) and Vilbaste (1953) have been reproduced by various subsequent authors (e.g., Lang 1954, Stojałowska 1961, Lokshina 1969. Thus, 14 centipede species and 27 millipede species were recorded from Estonia prior to the current study.

Material and methods
As complete as possible, bibliography of historical records of myriapods in Estonia was compiled, reviewing all the available faunistic studies and other records. The main Estonian zoological collections were searched for myriapod material (Estonian Museum of Natural History, Tallinn; Tartu University Museum of Natural history and the private insect collection of Allan Selin, Maardu). Some collections abroad known to house Estonian material were contacted for further information (Finnish Museum of Natural History and Zoologische Staatssammlung München, Germany).
New material was collected using: (1) pitfall traps, (2) Tullgren funnel and Kempson apparatus, (3) sifting moss, leaf litter and detritus with a standard entomological sieve, (4) manual searching in suitable habitats and daytime retreats, and (5) as bycatch of non-target species with window pane traps (attached to tree trunks) and Malaise traps (for particular description of the trapping projects, see Sammet et al. 2016 andTomasson et al. 2014, respectively).
The material was collected from 276 localities covering all parts of Estonia (see Table 1 and Figure 1 for details). The distribution of Estonian species  is presented in 50×50 km UTM grid, also used in the "Atlas of European Millipedes" (Kime andEnghoff 2011, 2017) (compiled using Adobe Photoshop CS5 Extended). The relative abundances in different habitats of species with at least 25 findings were presented as diagrams . The habitats studied repeatedly with different methods were grouped into 14 types: The barplot diagrams were produced by dividing the number of findings in a habitat type by the proportion of sampling effort in that particular habitat (i.e. the number of "sampling events" consisting of one trapping period or one hand collecting trip with subsequent Tullgren extraction of soil and litter samples) ( Figure 6). Other, more rare, habitats that were not studied with all the methods are not included. All studied material is preserved in 70% ethanol or a mix of ethanol and glycerol for Pauropoda. Some gonopods are preserved as microscope slides (using Euparal). The studied material is deposited in the entomological collection of Estonian University of Life Sciences (IZBE) and the soil biology collection of Tallinn University of Technology (TTUSB), both in Tartu, Estonia. Various keys for Central, Northern, and East, European myriapods were used for identification (Schubart 1934, Lokshina 1969, Zalesskaya 1978, Blower 1985, Andersson et al. 2005, Bonato et al. 2005, Barber 2009).

Results
All available material consisting of 1656 centipede, 4095 millipede, 29 symphylan, and six pauropod specimens were identified or re-identified and databased. The following list contains all the known published records of Estonian myriapods, followed by numbers of studied specimens and collecting localities. Full details for one finding from each locality are given in "Supplementary information". Only publications with original data are listed, subsequent ones citing these (e.g., Schubart 1934, Lang 1954, Stojałowska 1961, Lokshina 1969, Atlavinytė and Lokshina 1971, Blower 1985, Spuņģis 2010) are omitted. An asterisk (*) marks previously unpublished species. The full list of records with all details will be available through the Estonian eBiodiversity portal (http://elurikkus.ut.ee; Abarenkov et al. 2010) and Global Bi-  Table 1.  (Bonato et al. 2016), "Atlas of European millipedes" (Kime andEnghoff 2011, 2017) and McAlpine and Shear (2018) for centipedes and millipedes, respectively, and the "Catalogue of Myriapoda in the Nordic Countries" (Andersson et al. 2008(Andersson et al. , 2013 for Symphyla and Pauropoda. For each species, a brief overview of its distribution is given (with emphasis on North-Eastern Europe).  (Andersson et al. 2005), present also in southern Sweden and south-western Finland (Andersson et al. 2008), Latvia (Bonato et al. 2005) and Lithuania (Tuf et al. 2015).
Comments. A common species in different habitats, but absent in wet areas.
Comments. A common species in different habitats, but absent in wet areas. General distribution. Western Palaearctic species, present also in southern Sweden and south-western Finland (Andersson et al. 2008), Latvia (Bonato et al. 2005) and Lithuania (Tuf et al. 2015).

Geophilus truncorum
Comments. A common species in different habitats, especially in soil samples. Studied material. 5 specimens from 1 locality. General distribution. Western Palaearctic species, exclusively synanthropic in northern Europe, present also in Latvia (Bonato et al. 2005) and Finland (Andersson et al. 2008).
Comments. The species was recently shown to comprise several cryptic lineages (Wesener et al. 2015). It is probably an introduced species in Estonia (only found in the Tartu Botanical Garden in Estonia and present also only synanthropically in the neighbouring countries).
Comments. The species is more common in coastal areas and rare elsewhere. It seems to favour dry habitats.  General distribution. Mainly a Central European species but recently found also in Latvia (Bonato et al. 2005). The species has no published records from northwestern Russia (Volkova 2016), but there is a specimen collected from Izborsk (Pskov region, 10 km of Estonian border) in the IZBE collection.
Comments. The species is rare in Estonia. Both findings are from human settlements.
Comments. More common in western Estonia, found mainly in soil samples.  (Andersson et al. 2008).
Comments. Locally common in western Estonia, not found elsewhere.
Comments. A common species in different habitats.

General distribution.
Central-and south-east European species, present in Latvia (Trautberg 1929), Lithuania (Tuf et al. 2015) and on the Swedish islands Öland and Gotland (Andersson et al. 2008).
Comments. The species is widespread but rare in Estonia.
Comments. The species is widespread but infrequent in Estonia. Fig. 3(3)
Comments. The species is widespread but infrequent in Estonia, found only in bogs and boreo-nemoral forests.
Comments. A common species in different habitats, but avoids human settlements. H. Lohmander (1948) described a subspecies fennoscandicus Lohmander 1948 from Scandinavia, the description of which Estonian specimens generally match, but as the main subspecific difference concern colouration, more fresh specimens need to be studied.
Comments. The species is widespread but infrequent in Estonia, avoids wet habitats.
Comments. One of the two most common centipede species in different habitats, favours more fresh habitats than L. forficatus.

Polyzonium germanicum Brandt, 1837
Comments. The species is widespread but infrequent in different habitats, favours more fresh habitats and has not been found in human-disturbed areas.
Comments. This represents the first formal record of the species in Estonia after its mention by Saar and Takkis (2010) in the popular journal GEO. The species is widespread but favours fresh habitats. It seems to have recently colonised Estonia (but see Discussion). Fig. 3(9) Literature sources. Schubart 1930: 193, Vilbaste 1953 General distribution. Central European species absent from Scandinavia and Finland (Andersson et al. 2008(Andersson et al. , 2013, present in Lithuania (Atlavinytė and Lokshina 1971) formerly found from Latvia, but not recently recorded (Spuņģis 2010).

Mastigophorophyllon saxonicum Verhoeff, 1916
Comments. The species was described as frequent in southern Estonia (Schubart 1930) but there are no recent records since Vilbaste 1953. The species may have become more rare or extinct in Estonia. Schubart (1930) mentioned a few exact localities in his work, viz. Sõrve peninsula, Abruka Island, the vicinity of Pärnu and Vilbaste (1953) repeats these data and adds Tartu as the northern boundary of its range. All these localities were studied in the current research but the species was not found. It is possible that the record from Tartu refers instead to Haase's specimen of Craspedosoma mutabile var. fasciatum, interpreted as a misidentification of M. saxonicum by Schubart (1930). Vilbaste does not mention the species (nor any other Chordeumatids) in any of his later works. Fig. 3(11) Literature sources. Schubart 1930: 193, Vilbaste 1953: 19, Vilbaste 1970 Studied material. 14 specimens from 8 localities.
Comments. The species is widespread, but infrequent, in different habitats.
Comments. The species is widespread and common, in different habitats.
Comments. The species is widespread and common, in different habitats.

General distribution. Northern and central European species, present in Latvia
Comments. The species is widespread but rare.
Comments. The species is rare, found only in northern and western Estonia.
Comments. The species is widespread and common, especially in moist habitats, usually associated with decaying wood.
Comments. The species is widespread and common in different types of woodland. Climbs also in trees (as several individuals were found in trunk window traps).
Comments. The species is widespread but frequent only in western Estonia, mostly associated with open landscape. Fig. 4(5) Literature sources. Schubart 1930: 193  General distribution. Western Palaearctic species introduced to many parts of the world, rare in Latvia (Spuņģis 2010), present in Lithuania (Atlavinytė and Lokshina 1971) and southern Sweden, not found in Finland (Andersson et al. 2008(Andersson et al. , 2013.

Brachyiulus pusillus (Leach, 1814)
Comments. No specimens were collected during our studies or are preserved in Estonian collections. The current status of the species in Estonia is unclear as it has been reported as rare also in the past. It seems that both Schubart (1930) and Vilbaste (1953) refer to the same single specimen (loc. 20). There appears to be another finding from Hiiumaa Island according to Kime and Enghoff (2017), but we failed to trace the origin of that record (H. Enghoff, pers. comm.). It is not impossible that the record from Hiiumaa is a misinterpretation of the historical place name Tickhof, which is present also on Hiiumaa (Kongo 2016), but Schubart states the locality as "in einem Garten in Tickhof auf Ösel" -"in a garden in Tickhof on Ösel (=Saaremaa island)", and Vilbaste (1953) repeats that almost literally. *Cylindroiulus britannicus (Verhoeff, 1891) Fig. 4(6) Studied material. 10 specimens from 2 localities.

Cylindroiulus latestriatus (Curtis, 1845)
Comments. The species is widespread but infrequent, more common in western Estonia. It seems to prefer drier habitats. Fig. 4(9) Literature sources. Ivask 2011: 2, Ivask et al. in press. Studied material. 17 specimens from 7 localities. General distribution. Central and northern European species, not found in Latvia (Spuņģis 2010) and in Finland, present in southern Sweden (Andersson et al. 2008).

Julus scandinavius Latzel, 1884
Comments. The species is widespread but infrequent, most findings are from Western Estonia.
Comments. The species is common in western Estonia, but not found elsewhere.
Comments. The species is frequent in western Estonia, but rare elsewhere. Clearly prefers open landscapes.
Comments. The species is widespread, but common only in western Estonia. Clearly prefers open landscapes.
Comments. The species is widespread and very common in different habitats, with a slight preference to open landscape. The report of Ophyiulus pilosus in Estonia (Ivask 2011) has proved erroneous after re-examining the material, and belongs also to this species.

Rossiulus vilnensis (Jawlowski, 1925)
Comments. The species is widespread but infrequent, not found from northern Estonia.
Comments. The species is widespread and common, in different habitats, but avoids very wet ones and seems to be favoured by human influence.  (Atlavinytė and Lokshina 1971), Latvia (Spuņģis 2010) and southern Sweden, not found in Finland (Andersson et al. 2008(Andersson et al. , 2013.

Xestoiulus laeticollis
Comments. The species is infrequent and found only from Western Estonia.

Pauropoda
We regard the record of Pauropus huxleyi Lubbock, 1867 near Narva (Schmidt 1894, Andersson et al. 2005 being dubious, as it is unclear from which side of the current Estonian-Russian border it was collected and since several related species were undescribed at the time.    Studied material. 5 specimens from 1 locality. General distribution. Possibly a Holarctic species with predominantly a northern distribution, present also in Sweden and Finland (Andersson et al. 2005).
General distribution. Possibly a Holarctic species with introductions to South Asia and South America, present also in Sweden and Finland (Andersson et al. 2005).

Discussion
The current study adds six centipede and two millipede new country records, while two millipedes, viz. Polydesmus coriaceus and Ophyiulus pilosus are presently removed from the Estonian checklist. All the Symphylan and Pauropod species represent new records.
It is unclear whether the new records are due to insufficient previous data (which may well be true for centipedes, except Stenotaenia linearis) or range shifts. The human or climate driven range shifts up to over hundred km northwards in recent decades have been also detected elsewhere (David 2009). The changes in occurrence frequencies of the species that have been observed also in the neighbouring countries, e.g., in Finland by Lehtinen and Terhivuo (1996), concern Cylindroiulus caeruleocinctus and Unciger foetidus. Both species were earlier reported as rare in Estonia (cf. Vilbaste 1953) but proved to be common and widespread after the present study. Mass outbreaks of some julid species have also spread northwards (Kania and Tracz 2005) Andersson et al. 2005, but absent according to Kime 2001). However, we failed to find the original source of the Finnish records (V. Huhta, H. Enghoff, P. Djursvoll, P. Cardoso pers. comm.). The actual appearance of C. raulinsii in the Northern Baltic region can be decades earlier, as the myriapod fauna of Estonia and Latvia was not systematically monitored in the 1980-s and 1990-s. On the other hand, if the record of Craspedosoma mutabile var. fasciatum (if a synonym of C. raulinsii, as in Sierwald and Spelda 2018) from Tartu (Haase 1886) is correct, the species distribution range may have fluctuated also in the past. The name is a synonym of Mastigona bosniense according to Schubart (1934), and the identity with that species is also possible, as a specimen of Mastigona sp. (as Heteroporatia sp.) has been found in Latvia (Becker 1929, Spuņģis 2010. Four species, viz. Strongylosoma stigmatosum, Cylindroiulus punctatus, Archiboreiulus pallidus and Choneiulus palmatus, occurring in neighbouring Latvia and/or Finland might be found also in Estonia, but more studies, especially in southern Estonia are needed. The species Mastigophorophyllon saxonicum, previously reported from many localities in southern Estonia was not re-found, and appears to have become more rare or extinct (which is also the case in Latvia, Spuņģis 2010). Spuņģis (2010) discusses the possibility that the northern Baltic records of M. saxonicum are misidentifications of C. raulinsii, which seems improbable to us as both species should have been well known for O. Schubart. Several species e.g., Lamyctes emarginatus, Pachymerium ferrugineum, Julus terrestris, Julus scandinavius, Allajulus nitidus, Leptoiulus cibdellus, and Xestoiulus laeticollis are more common in western Estonia or even restricted to this region characterised by milder maritime climate and calcareous soils e.g., Geophilus carpophagus, Boreoiulus tenuis, Julus scanicus, and Cylindroiulus britannicus.
The currently known fauna of Estonian Diplopoda and Chilopoda is quite similar to the neighbouring regions. 79% of the species are shared with Finland and 87.5 % are shared with Latvia. The similarity to Latvian fauna may be in fact even higher, as several species occurring both in Estonia and Lithuania might be present also in Latvia. Estonian Symphyla and Pauropoda deserve further attention. At present, they remain too poorly known to allow for any comparisons.