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An overview of Estonian woodlice (Isopoda, Oniscidea)
expand article infoKaarel Sammet, Getriin Orgusaar§, Mari Ivask|, Olavi Kurina
‡ Estonian University of Life Sciences, Tartu, Estonia
§ University of Tartu, Tartu, Estonia
| Tallinn University of Technology, Tartu, Estonia
Open Access

Abstract

An overview of the Estonian terrestrial isopod fauna is given, based on literature data and material collected from 1984 to 2021. The identified material consisted of 10915 specimens belonging to 14 species and collected from 172 localities throughout Estonia. In combination with previous data from the literature data, there are now reliable records of 16 species of woodlice from Estonia. Two species, viz. Platyarthrus hoffmannseggii Brandt, 1833 and Hyloniscus riparius (C. Koch, 1838), are new for the fauna. The latter has probably colonised Estonia recently and range expansions have been reported elsewhere. The data on Philoscia muscorum (Scopoli, 1763) are dubious, and this species is currently excluded from the Estonian list.

Keywords

Estonia, Oniscidea, range shifts, soil arthropods

Introduction

The knowledge on Estonian terrestrial isopods is scattered in various publications, without a modern overview of the fauna. Some publications are in Estonian and may be thus inaccessible to the wider audience.

Data on this group were first given by J. B. Fischer, who mentioned the presence of Oniscus asellus Linnaeus in Livonia (Fischer 1778: 167), an earlier administrative division, which covered the southern part of present-day Estonia and northern Latvia. The identity of the abovementioned species is unclear, as most of European species were yet to be described. At the beginning of 20th century, W. Herold collected material in many places in Estonia and Latvia, published the results in several works (Herold 1927, 1928, 1930), and provided the first reliable overview of the fauna, which included 13 Estonian species. Later, Estonian entomologist J. Vilbaste published new records in three local faunistic studies (Vilbaste 1970; Vilbaste et al. 1985; Vilbaste and Vilbaste 1993) and K. Remm added one record (Remm 1988).

A lot of unidentified material from various research projects and fieldwork made over many years (1984–2020) has been stored in the entomological collection of Estonian University of Life Sciences (including the zoological collections of the former Institute of Zoology and Botany of the Estonian Academy of Sciences) and Tallinn University of Technology (TalTech) soil biology laboratory. Based on these materials and literature records, an account of the current knowledge is given below.

Material and methods

As complete as possible, a bibliography of historical records of terrestrial isopods in Estonia was compiled. New material was collected using: (1) pitfall traps, (2) Tullgren funnels, (3) sifting moss, leaf litter, and detritus with standard entomological sieves, (4) manual searching in suitable habitats, and (5) as bycatch of non-target species with window traps (attached to tree trunks; Sammet et al. 2016) and Malaise traps (for details of the Estonian Malaise trap project, see Tomasson et al. 2014). The material was collected from 172 localities throughout Estonia (Table 1; Figure 1). All studied material is preserved in 80% ethanol and deposited in the entomological collection of Estonian University of Life Sciences (IZBE) and soil biology laboratory of TalTech Tartu College (TTUSB), both in Tartu, Estonia. Various keys for European woodlice were used for identification (Palmén 1946; Frankenberger 1959; Vandel 1960, 1962; Gruner 1966; Oliver and Meecham 1993). The distributions of Estonian species (Fig. 5) are presented in a 50 × 50 km UTM grid (compiled using Adobe Photoshop CS5 Extended). The images of the general habitus were combined using the LAS V.4.1.0 software from multiple gradually focused images of the specimens in alcohol taken by a Leica DFC 450 camera attached to Leica 205C stereomicroscope.

Figure 1. 

Collecting localities of Estonian Oniscidea and numbers of sampled localities per 50 × 50 km UTM squares. For further details, see Table 1.

Table 1.

Collecting localities of Estonian Oniscidea. The localities’ numbers correspond to those on Figure 1. Localities within a range of less than 10 km are presented by one number, the different place names (sub-localities) under one number are designated consecutive letters (the coordinates apply only to the first of them).

No. Latitude, Longitude Name Methods used
1 58.3132°N, 21.9089°E a Eeriksaare 1, b Eeriksaare 2, c Kõruse 1, d Kõruse 2, e Tammese, f Neeme manual collecting; pitfall trapping; Tullgren funnel
2 58.3009°N, 21.9351°E a Atla 1, b Atla 2, c Atla 3 manual collecting; pitfall trapping
3 57.9767°N, 21.9954°E a Türju, b Sõrve south manual collecting; pitfall trapping
4 58.2731°N, 22.0114°E a Leedri, b Kipi, c Viidu-Mäebe, d Audaku, e Sutru, f Nakimetsa, g Pitkasoo sifting soil and litter; manual collecting; pitfall trapping, Tullgren funnel
5 58.1213°N, 22.1966°E Kaugatoma manual collecting; pitfall trapping
6 58.0000°N, 22.1667°E Viieristi manual collecting
7 58.5167°N, 22.2167°E a Mustjala, b Kugalepa, c Panga manual collecting; Tullgren funnel
8 58.3186°N, 22.3057°E a Mõnnuste, b Paadla manual collecting; pitfall trapping
9 58.2425°N, 22.4249°E Nasva manual collecting; pitfall trapping
10 58.2496°N, 22.4800°E Kuressaare manual collecting; pitfall trapping
11 58.9445°N, 22.4361°E a Paope b Reigi manual collecting; pitfall trapping
12 58.1225°N, 22.5013°E Abruka manual collecting; Tullgren funnel
13 58.3005°N, 22.6337°E Ilpla manual collecting; pitfall trapping
14 58.2433°N, 22.6741°E a Vanamõisa 1, b Vanamõisa 2, c Vanamõisa 3 manual collecting; pitfall trapping
15 58.4563°N, 22.7076°E a Tika, b Võrsna manual collecting; pitfall trapping; Tullgren funnel
16 58.7683°N, 22.8143°E Kassari manual collecting; pitfall trapping
17 58.8639°N, 22.9836°E a Aruküla 1, b Aruküla 2, c Saarnaki, d Heltermaa, e Sarve manual collecting; pitfall trapping; Tullgren funnel
18 58.7769°N, 23.0472°E a Hanikatsi, b Langekare manual collecting; pitfall trapping
19 58.5842°N, 23.0236°E Orinõmme manual collecting; pitfall trapping
20 58.4389°N, 23.0681°E Asva 1 manual collecting; pitfall trapping
21 58.5557°N, 23.0879°E Orissaare manual collecting; pitfall trapping
22 58.6132°N, 23.0850°E Koguva manual collecting; pitfall trapping
23 58.7421°N, 23.1349°E Ahelaid Tullgren funnel
24 58.6412°N, 23.1536°E a Paenase, b Pallasmaa, c Nõmmküla, d Üügu manual collecting; pitfall trapping; Tullgren funnel
25 58.9917°N, 23.1928°E Vormsi manual collecting; pitfall trapping; Tullgren funnel
26 58.4617°N, 23.2111°E a Kahtla, b Kübassaare manual collecting; pitfall trapping Tullgren funnel
27 57.8006°N, 23.2283°E a Ruhnu 1, b Ruhnu 2 manual collecting; window pane trap
28 58.5786°N, 23.2653°E a Mäla 1, b Mäla 2, c Võiküla 3, d Võiküla 1 manual collecting; pitfall trapping
29 58.6501°N, 23.3133°E a Lõetsa 1, b Lõetsa 2 manual collecting; pitfall trapping
30 58.6413°N, 23.5133°E Hanila manual collecting; pitfall trapping
31 58.5880°N, 23.5286°E a Virtsu, b Puhtu, c Laelatu, d Pivarootsi manual collecting; pitfall trapping; Tullgren funnel
32 59.0084°N, 23.6934°E Linnamäe manual collecting; pitfall trapping
33 58.5337°N, 23.8299°E Paadermaa manual collecting; pitfall trapping
34 58.8312°N, 23.8785°E a Keskvere, b Patsu manual collecting; pitfall trapping; Tullgren funnel
35 58.3818°N, 23.9810°E a Ermistu, b Tõhela manual collecting; pitfall trapping; Tullgren funnel
36 58.9020°N, 24.0287°E a Marimetsa, b Kullamaa 1, c Kullamaa 2 manual collecting; Tullgren funnel
37 58.9947°N, 24.0559°E Risti manual collecting; Tullgren funnel
38 58.6455°N, 24.1253°E Kurese manual collecting; Tullgren funnel
39 58.7760°N, 24.2496°E Vigala manual collecting; Tullgren funnel
40 58.8960°N, 24.3758°E Sõtke manual collecting; pitfall trapping; Tullgren funnel
41 58.3864°N, 24.3695°E a Valgeranna, b Pärnu manual collecting; Tullgren funnel
42 58.0195°N, 24.4532°E Kabli manual collecting; Tullgren funnel
43 58.0807°N, 24.4889°E a Häädemeeste, b Palitsa manual collecting; Tullgren funnel
44 58.2429°N, 24.4965°E Tahkuranna manual collecting; Tullgren funnel
45 59.3339°N, 23.9703°E Väike-Pakri manual collecting; Tullgren funnel
46 59.5933°N, 24.5025°E Naissaar manual collecting; Tullgren funnel
47 59.4425°N, 24.5228°E a Rannamõisa MKA b Muraste c Tõmmiku manual collecting; pitfall trapping; Tullgren funnel
48 59.3411°N, 24.6386°E a Tänassilma cave, b Vana-Mustamäe manual collecting; pitfall trapping; Tullgren funnel
49 59.2661°N, 24.6483°E Kasemetsa manual collecting; Tullgren funnel
50 59.4293°N, 24.7777°E central Tallinn manual collecting; Tullgren funnel
51 59.5297°N, 24.8578°E Lubja manual collecting; Tullgren funnel
52 59.2378°N, 24.9311°E Sõmeru manual collecting; Tullgren funnel
53 59.4631°N, 24.9378°E a Maardu, b Muuga, c Ülgase cave manual collecting; pitfall trapping; Tullgren funnel
54 58.9703°N, 24.7294°E a Kuusiku, b Raela, c Raikküla manual collecting; pitfall trapping; Tullgren funnel
55 58.3333°N, 25.3000°E Kõpu manual collecting; Tullgren funnel
56 58.1562°N, 25.3390°E Koodioru manual collecting
57 58.1557°N, 25.4360°E a Halliste, b Viivre manual collecting; pitfall trapping; Tullgren funnel
58 59.0835°N, 25.4053°E Mustla manual collecting; Tullgren funnel
59 58.8893°N, 25.5725°E Paide manual collecting; Tullgren funnel
60 58.6304°N, 25.6196°E a Koksvere, b Kirivere, c Kõo manual collecting; Tullgren funnel
61 58.3738°N, 25.6127°E Viljandi manual collecting; Tullgren funnel
62 59.2553°N, 25.6669°E Aegviidu manual collecting; Tullgren funnel
63 59.6049°N, 25.9230°E a Käsmu, b Natturi manual collecting; pitfall trapping; Tullgren funnel
64 58.6548°N, 25.9685°E Põltsamaa manual collecting; Tullgren funnel
65 58.5332°N, 25.9468°E a Kolga-Jaani, b Lalsi manual collecting; Tullgren funnel
66 58.9996°N, 26.1168°E Liigvalla manual collecting; Tullgren funnel
67 59.0970°N, 26.1826°E Vao manual collecting; Tullgren funnel
68 59.2742°N, 26.1955°E a Lasila, b Karunga, c Levala manual collecting; pitfall trapping; Tullgren funnel
69 59.0233°N, 26.2444°E Kamariku manual collecting; pitfall trapping; Tullgren funnel
70 58.8669°N, 26.2625°E a Tooma, b Kärde manual collecting; pitfall trapping; Tullgren funnel
71 58.5948°N, 26.3631°E a Kursi, b Tõrve, c Altnurga manual collecting; Tullgren funnel
72 58.1072°N, 26.2767°E Atra manual collecting; pitfall trapping; Tullgren funnel
73 58.2066°N, 26.3825°E a Käärdi, b Peedu manual collecting; pitfall trapping; Tullgren funnel
74 57.5962°N, 26.2855°E Olina manual collecting; Tullgren funnel
75 57.7193°N, 26.5000°E Mähkli manual collecting; Tullgren funnel
76 57.8611°N, 26.5241°E Vana-Antsla manual collecting; Tullgren funnel
77 57.9510°N, 26.4368°E Ilmjärve manual collecting; Tullgren funnel
78 58.0062°N, 26.6073°E Kaagvere manual collecting; Tullgren funnel
79 57.5727°N, 26.6413°E Mõisamõtsa manual collecting; Tullgren funnel; window pane trap
80 58.5604°N, 26.6285°E Valgma manual collecting; Tullgren funnel
81 58.4103°N, 26.6394°E a Tiksoja, b Tähtvere bog, c Õssu, d Maramaa, e TartuTähtvere, f Tartu central, g Tartu Aardla, h Raadi, I Aruküla cave manual collecting; pitfall trapping; Tullgren funnel
82 58.2302°N, 26.7011°E Kambja manual collecting; Tullgren funnel
83 58.5950°N, 26.7719°E a Tüükri, b Kalvi, c Oru, d Aseri manual collecting; pitfall trapping; Tullgren funnel
84 59.3019°N, 26.8818°E a Ilmaste, b Nüri, c Aidu manual collecting; pitfall trapping; Tullgren funnel
85 59.2289°N, 27.3247°E Mäetaguse NR window pane trap
86 59.4448°N, 27.3348°E Valaste manual collecting; Tullgren funnel
87 58.7841°N, 26.9330°E a Nõmme b Ruskavere manual collecting; pitfall trapping; Tullgren funnel
88 58.7279°N, 26.8260°E Odivere manual collecting; pitfall trapping; Tullgren funnel
89 58.5170°N, 26.9224°E a Välgi b Pataste manual collecting; pitfall trapping; Tullgren funnel
90 58.6033°N, 27.1304°E Alatskivi manual collecting; Tullgren funnel
91 58.4968°N, 27.2376°E Varnja manual collecting; Tullgren funnel
92 58.2750°N, 27.3250°E Järvselja manual collecting; sifting soil and litter; Tullgren funnel
93 58.1148°N, 27.0474°E Saessaare manual collecting; Tullgren funnel
94 58.0965°N, 27.4744°E Ristipalo manual collecting; Tullgren funnel
95 57.7447°N, 27.3335°E a Möldri b Parmu manual collecting; Tullgren funnel
96 57.8433°N, 27.4655°E Piusa manual collecting; Tullgren funnel
97 59.3573°N, 28.1970°E Narva manual collecting; Tullgren funnel

Results

Altogether 14142 specimens were collected. Of these, 10915 were identified to the species level. The following list contains all the known published records of Estonian woodlice, followed by numbers of studied specimens and collecting localities. Full details for each record from each locality are given in Suppl. material 1. An asterisk (*) indicates a species new to Estonia. 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 Biodiverdsity Information Facility (https://www.gbif.org). Nomenclature and synonymics follow Schmalfuss (2003).

Ligiidae

Ligidium hypnorum Cuvier, 1792

Figs 4B, 5A

Published sources. Herold 1930: 478–479; Vilbaste and Vilbaste 1993: 317.

Studied material. 117 specimens from 13 localities (loc. 30a, 47b, 47c, 54c, 57b, 83c, 87a, 87b, 88a, 89a, 92a, 95a, 95b).

Comments. A locally abundant species, with no records from Estonian islands. It has been described as widespread in Estonia also in the past (Herold 1930). The findings are from different habitats: fresh to mesic forests, meadows, arable fields and gardens. Present also in Lithuania (Vilisics et al. 2012) and Latvia (Spuņģis 2008) but not Finland (Boxshall G 2013).

Trichoniscidae

Trichoniscus pusillus Brandt, 1833

Figs 3A, 5B

Published sources. Herold 1927: 6; Herold 1928: 215; Herold 1930: 479 (as T. elisabethae Herold, 1923; T. elisabethae var. estoniensis Herold, 1927; T. caelebs Verhoeff, 1917); Vilbste 1970: 170 (as T. pusillus caelebs Vh.); Vilbaste et al. 1985: 151 (as T. pusillus caelebs Vh.); Remm 1988: 127 (as T. pusillus caelebs Vh.); Vilbaste and Vilbaste 1993: 317.

Studied material. 117 specimens from 24 localities (loc. 1e, 4d, 17a, 23b, 25a, 34a, 35a, 39a, 40c, 47a, 50a, 51a, 57a, 58c, 68a, 74a, 78a, 78b, 78e, 80a, 80d, 83a, 89b, 92a).

Comments. Once reported as the most common species of Trichoniscidae (e.g. Herold 1927, 1930), the species appears to have become less abundant. It is widespread in various habitats (bogs, different types of forests, meadows, and urban areas), but is more common in moist habitats and is often associated with decaying wood. The species is known to be mainly parthenogenetic (Gruner 1966; De Smedt et al 2016), and the collected material consisted only of female specimens. Thus, no male characters were available for study and it cannot be ruled out that some specimens were misidentified and other Trichoniscus species may also be present in Estonia as very rare (e.g. T. provisorius or T. pygmaeus). The taxonomic status of the described varieties T. elisabethae Herold, 1923 and T. elisabethae var. estoniensis Herold, 1927 is unclear, but we follow the Schmalfuss (2003) catalogue and treat them as T. pusillus. Present also in Latvia (Spuņģis 2008) and Finland (Palmén 1946; Vilisics and Terhivuo 2009).

* Hyloniscus riparius (C. Koch, 1838)

Figs 3B, 5C

Studied material. 202 specimens from 22 localities (loc. 12a, 23b, 35b, 39a, 39a, 49a, 50a, 52b, 53a, 55b, 57a, 58b, 59a, 60b, 61a, 69c, 70b, 78a, 78e, 78g, 83a, 85a).

Comments. The species is widespread and common, but has only recent records and is probably extending its range in the Europe. It has been often found in human settlements, but also seashore habitats and different types of forests, except the very dry ones. Present also in Latvia (Spuņģis 2008) and Finland (Vilisics and Terhivuo 2009).

Haplophthalmus mengii (Zaddach, 1844)

Fig. 5D

Published source. Herold 1930: 479–480.

Comments. Reported as rare, with only one finding locality in northern Estonia (Herold 1930). No recent records. Present also in Latvia (Spuņģis 2008) and Finland (Palmén 1946).

Platyarthridae

* Platyarthrus hoffmannseggii Brandt, 1833

Figs 4A, 5E

Studied material. 3 specimens from 1 locality (loc. 80g).

Comments. A myrmecophilous species, found from a nest of Lasius niger (Linnaeus, 1758). There are no records from the northern Baltic region so far, but it has recently been found in Lithuania (Šatkauskienė 2017), and a population has also been found in Finland (Lehtinen 1961). However, due to the destruction of the only known locality, the species could be extinct there now (Vilisics and Terhivuo 2009).

Trachelipodidae

Trachelipus rathkii (Brandt, 1833)

Figs 2A, 5F

Published sources. Herold 1927: 52 (as Porcellio rathkei); Herold 1930: 476 (as Tracheoniscus rathkei (Brandt, 1833)); Vilbaste 1970: 170 (as Tracheoniscus rathkei (Brandt, 1833)); Vilbaste et al. 1985: 151 (as Tracheoniscus rathkei (Br.)).

Studied material. 3180 specimens from 114 localities (loc. 1a, 1c, 1e, 1f, 3a, 3b, 4c, 6a, 7a, 9a, 9b, 10a, 10b, 11a, 12a, 13a, 14b, 15a, 15b, 16a, 17a, 17b, 17c, 17d, 18a, 18b, 18c, 19a, 20a, 21a, 22a, 23a, 23b, 23c, 25a, 27a, 28a, 28b, 29a, 30a, 30c, 30d, 33a, 33b, 34a, 34b, 35b, 35b, 35c, 35c, 37a, 38a, 39a, 40a, 40b, 41a, 41b, 42a, 46b, 51a, 51b, 52a, 52b, 53a, 55a, 56a, 57a, 58a, 58b, 59a, 60b, 61a, 62a, 63b, 64a, 65a, 66a, 66b, 66c, 66c, 67a, 68b, 69a, 69b, 70a, 71a, 72a, 73a, 76a, 77a, 78a, 78d, 78e, 78f, 78f, 79a, 80a, 80b, 80c, 80d, 81a, 81b, 81c, 82a, 83a, 84a, 85a, 86a, 87a, 90a, 91a, 91b).

Comments. One of the most common species in Estonia, in all kinds of habitats (both anthropogenic and natural, except bogs). It has also been described as widespread and common in Estonia in the past (Herold 1927, 1930). Present also in Leningrad region (European Russia, Kuznetsova and Gongalsky 2012), Latvia (Spuņģis 2008), and Finland (Palmén 1946).

Porcellionidae

Porcellio scaber Latreille, 1804

Figs 2B, 5G

Published sources. Herold 1927: 52; Herold 1930: 481; Vilbaste et al. 1985: 151.

Studied material. 217 specimens from 13 localities (loc. 3b, 24a, 26a, 26b, 30b, 35c, 46b, 48a, 63a, 78c, 78e, 78f, 84a).

Comments. The species was described as purely synanthropic in continental Estonia and free-living in western Estonian islands (Herold 1927, 1930). The studied material contains findings from and outside of human settlements (including different forests, grasslands, and seashore) both from western islands and continent. Present also in Novgorod region (European Russia, Kuznetsova and Gongalsky 2012), Latvia (Spuņģis 2008), and Finland (Palmén 1946).

Porcellio spinicornis Say, 1818

Figs 2C, 5H

Published sources. Herold 1927: 52; Herold 1930: 481 (as P. pictus Brandt, 1833); Vilbaste et al. 1985: 151 (as P. pictus Br.).)

Studied material. 68 specimens from 19 localities (loc. 4b, 6b, 20b, 32a, 35b, 39a, 40b, 46a, 51c, 52b, 60a, 61a, 78f, 78h, 78i, 84a, 89a, 93a, 97).

Comments. A common and widespread species, often found on stone walls in human settlements, but also in mesic deciduous forests. Present also in Leningrad region (European Russia, Kuznetsova and Gongalsky 2012), Latvia (Spuņģis 2008), and Finland (Palmén 1946).

Porcellionides pruinosus (Brandt, 1833)

Published source. Herold 1930: 476.

Comments. No recent records. This species has been described as purely synanthropic in Estonia (Herold 1930). Present also in Latvia (Spuņģis 2008) and Finland (Palmén 1946).

Cylisticidae

Cylisticus convexus (De Geer, 1778)

Figs 2D, 5I

Published sources. Herold 1927: 51; 480 Herold 1930: 480.

Studied material. 825 specimens from 5 localities (loc. 46b, 66a, 78e, 78f, 78g).

Comments. This species is widespread and locally quite abundant, both in human settlements and in forests, under stones or in rotten logs. It has been described as widespread and mainly synanthropic in Estonia by W. Herold, with free-living populations in northern and western Estonian islands (Herold 1930). Present also in Latvia (Spuņģis 2008) and Finland (Palmén 1946).

Oniscidae

Oniscus asellus Linnaeus, 1758

Figs 2E, 5J

Published sources. Fischer 1778: 167 (questionable; see comment in Introduction); Herold 1930: 480.

Studied material. 433 specimens from 5 localities (loc. 4b, 6, 36b, 47b, 48b).

Comments. The species seems to be free-living on the island of Saaremaa, but synanthropic and sometimes quite abundant elsewhere. Herold (1930) described it as being widespread but purely synanthropic in Estonia. Present also in Latvia (Spuņģis 2008), Pskov region (European Russia, Kuznetsova and Gongalsky 2012), and Finland (Palmén 1946).

Armadillidiidae

Armadillidium opacum (Koch, 1841)

Figs 3D, 5K

Published sources. Herold 1927: 53; Herold 1930: 483–485; Vilbaste et al. 1985: 151.

Figure 2. 

Habitus of Estonian Oniscidea species A Trachelipus rathkii B Porcellio scaber C Porcellio spinicornis D Cylisticus convexus E Oniscus asellus. Scale bars: 2 mm.

Figure 3. 

Habitus of Estonian Oniscidea species A Trichoniscus pusillus B Hyloniscus riparius C Armadillidium zenckeri D Armadillidium opacum E Armadillidium pulchellum. Scale bars: 1 mm.

Figure 4. 

Habitus of Estonian Oniscidea species A Platyarthrus hoffmannseggii B Ligidium hypnorum. Scale bars: 0.5 mm (A); 1 mm (B).

Studied material. 5294 specimens from 44 localities (loc. 1a, 1b, 1c, 1d, 1e, 1f, 2a, 2b, 2c, 4b, 5a, 6a, 8a, 8c, 9a, 9b, 11a, 13a, 14a, 14b, 14c, 14c, 15b, 16a, 17a, 17b, 17c, 17d, 18b, 19a, 20a, 21a, 23a, 23c, 25a, 25b, 27a, 28a, 28b, 29a, 30a, 30d, 31a, 35a, 37a).

Comments. Very common in western Estonia and islands (in forests, grasslands, and coastal habitats) but rare elsewhere. Present also in Latvia (Spuņģis 2008) and Finland (Palmén 1946).

Armadillidium pictum Brandt, 1833

Fig. 5L

Published sources. Herold 1927: 53; Herold 1930: 482–483.

Studied material. 5 specimens from 3 localities (loc. 28a, 44a, 45a).

Comments. A rare species found only in northern Estonia and Muhu island in coastal habitats (broad-leaved forest under limestone escarpment, pine forest near seashore, alvar grassland). Present also in Latvia (Spuņģis 2008) and Finland (Palmén 1946).

Figure 5. 

Distribution of Estonian Oniscidea. Red denotes studied specimens (1984–2020), blue = literature data 1970–1993, yellow = literature data 1927–1930 A Ligidium hypnorum B Trichoniscus pusillus C Hyloniscus riparius D Haplophthalmus mengii E Platyarthrus hoffmannseggii F Trachelipus rathkii G Porcellio scaber H Porcellio spinicornis I Cylisticus convexus J Oniscus asellus K Armadillidium opacum L Armadillidium pictum M Armadillidium pulchellum N Armadillidium zenckeri O Armadillidium vulgare. Porcellionides pruinosus has been omitted since the published source mentions no specific localities.

Armadillidium pulchellum (Zenker, 1798)

Figs 3E, 5M

Published sources. Herold 1930: 481–482; Vilbaste et al. 1985: 151.

Studied material. 1 specimen from 1 locality (loc. 4d).

Comments. A rare species found only on Saaremaa island in western Estonia (in a spring fen). Present also in Latvia (Spuņģis 2008) and Finland (Palmén 1946).

Armadillidium vulgare (Linnaeus, 1758)

Fig. 5O

Published source. Chinery 2005: 300.

Studied material. 1 specimen from 1 locality (loc. 81a).

Comments. A rare synanthropic species with only one finding from Estonia (from suburban area in Tartu). Present also in Latvia (Spuņģis 2008) and Finland (Palmén 1946).

Armadillidium zenckeri Brandt, 1833

Figs 3C, 5N

Published sources. Herold 1927: 53; Herold 1930: 485–490; Vilbaste 1970: 170; Vilbaste et al. 1985: 151.

Studied material. 452 specimens from 44 localities (loc. 1a, 1b, 1d, 1e, 1f, 2a, 2b, 2c, 3a, 4a, 4c, 4e, 5a, 7a, 8b, 9a, 9b, 11a, 13a, 14a, 14b, 15b, 16a, 17a, 17b, 17c, 17d, 19a, 20a, 21a, 23a, 23b, 23c, 25a, 28a, 28b, 29a, 30a, 30d, 36a, 37a, 37a, 37a, 43a).

Comments. Common in western Estonia and islands, but rare elsewhere. Present in dry to mesic forests and different grasslands. Present also in Latvia (Spuņģis 2008) and Finland (Palmén 1946).

Discussion

There are reliable records of 16 species of terrestrial isopods from Estonia. One species has been dubiously claimed to occur in Estonia, and it is presently not included in the checklist. We failed to find any records or specimens to support the occurrence of Philoscia muscorum (Scopoli, 1763) in Estonia, although marked as “present” in Fauna Europaea database (Boxshall G 2013). The species is, however, present in the neighbouring Latvia (Spuņģis 2008), and its occurrence in Estonia is not impossible. Two species, viz. Haplophthalmus mengii (Zaddach, 1844) and Porcellionides pruinosus (Brandt, 1833), have not been recently collected and are included here based on literature records only. The fauna is very similar to neighbouring Latvia and southern Finland, with which all species shared, except for Ligidium hypnorum and P. hoffmannseggii, but the apparent absence of the latter in Latvia can be possibly explained by its rarity and lack of studies in its specific habitat (ant nests). Comparing the recent records with older ones, it seems that the distribution and abundance of some species have remained approximately the same over the past century, whereas some other species appear to have become rarer or have expanded their ranges. Porcellio scaber was reported as a synanthropic species in continental Estonia (Herold 1930), but we found it also in the field there. The same applies to Oniscus asellus. The existing Baltic records of Hyloniscus riparius are from Lithuania and southern Latvia (Spuņģis 2008; Tuf et al. 2014). The first Estonian records are from 2015, and given that the species was found during the 2003–2007 studies only in south-western Latvia (Spuņģis 2008), its range may have shifted remarkably quickly (by more than 300 km northwards in only a decade). An expansion of the species range northwards and eastwards has also been detected in European Russia in recent decades (Gongalsky et al. 2013) and has recently reached also the Russian Far East (Gongalsky and Kuznetsova 2021). The first Finnish record of the species was from a greenhouse in 1946, but the first finding outside dates from 2007 (Vilisics and Terhivuo 2009). Several species are only found or are more common in western and northern Estonia, characterized by milder maritime climate and calcareous soil (Armadillidium opacum, A. pictum, A. pulchellum, A. zenckeri, Haplophthalmus mengii). Seven species are known from areas neighbouring Estonia and may have been not collected due to rarity or very local distribution: Porcellium conspersum (C.Koch, 1841), Philoscia muscorum (Scopoli, 1763), Haplophthalmus danicus Budde-Lund, 1879, Porcellio dilatatus Brandt, Porcellio laevis Latreille, 1804, and Armadillidium nasatum Budde-Lund 1885. The range of Trichoniscus provisorius Racovitza, 1908 reaches Poland (Jędryczkowski 1979), and there are other widespread Trichoniscus species, e.g. T. alemannicus or T. pygmaeus Sars 1898, in central Europe (the latter reaching southern Russia in the east; Kuznetsova and Gongalsky 2012), but due to lack of male specimens these species may remain as yet undetected in the Baltic countries. Introduced species can sometimes be found in greenhouses and may be expected to be found in the future too; several of the 25 species found in Finland (Vilisics and Terhivuo 2009) are found only indoors. It seems probable that the number of naturally occurring species might be closer to 19 as in neighbouring Latvia (Spuņģis 2008).

Acknowledgements

We would like to thank Mart Meriste, Ilmar Süda, Tõnu Talvi, Allan Selin, Urmas Jürivete, Tõnu Kesküla, Märt Kruus, Heli Kirik, Erki Õunap, Miina Oras, Elisabeth Prangel, Ene Kook and Hannes Järve who collected material for the present study. We are also grateful to Konstantin Gongalsky and Ferenc Vilisics for the helpful comments to the initial draft of the manuscript. This work was partially financed by Estonian Environmental Board grant “Large-scale restoration of calcareous grasslands, implications for biodiversity” (3-2_7/8555-5/2018) and funding programme RITA “Enhancing farmland biodiversity” (2014-2020.4.02.16-0025).

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Supplementary material

Supplementary material 1 

Supplementary data

Kaarel Sammet

Data type: occurences

Explanation note: Finding details of studied Estonian Oniscidea specimens from each locality (repeated findings from exactly the same locality are omitted).

This dataset is made available under the Open Database License (http://opendatacommons.org/licenses/odbl/1.0/). The Open Database License (ODbL) is a license agreement intended to allow users to freely share, modify, and use this Dataset while maintaining this same freedom for others, provided that the original source and author(s) are credited.
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