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Confirmation of Metatrichoniscoides leydigii (Weber, 1880) in Belgium, 60 years after discovery (Isopoda: Trichoniscidae)

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Abstract

The woodlouse Metatrichoniscoides leydigii (Weber, 1880) was first recorded from Belgium in 1954. However, the collected individuals were all females incapacitating identification to species level. More intensive surveys in the autumn of 2015 revealed many new recordings with the discovery of the first male individuals. Finally, the species could be confirmed for Belgium after more than 60 years after its first discovery. The species seems to be quite common on clay soils in the northwestern part of the country.
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Bulletin de la Société royale belge d’Entomologie/Bulletin van de Koninklijke Belgische Vereniging voor Entomologie, 152 (2016): 18-21
Confirmation of Metatrichoniscoides leydigii (Weber, 1880) in Belgium,
60 years after discovery (Isopoda: Trichoniscidae)
Pallieter DE SMEDT1,2, Pepijn BOERAEVE2 & Gert ARIJS2
1 Forest & Nature Lab, Ghent University, Geraardsbergsesteenweg 267, B-9090 Melle (Gontrode), Belgium
(email: Pallieter.desmedt@ugent.be)
2 SPINICORNIS, Mispeldonk 2, B-2820 Bonheiden, Belgium (email: info@spinicornis.be)
Abstract
The woodlouse Metatrichoniscoides leydigii (Weber, 1880) was first recorded from Belgium in 1954.
However, the collected individuals were all females incapacitating identification to species level. More
intensive surveys in the autumn of 2015 revealed many new recordings with the discovery of the first
male individuals. Finally, the species could be confirmed for Belgium after more than 60 years after its
first discovery. The species seems to be quite common on clay soils in the north-western part of the
country.
Keywords: Metatrichoniscoides leydigii; isopods; woodlice; distribution; Belgium.
Samenvatting
De pissebed Metatrichoniscoides leydigii (Weber, 1880) (Nederlandse naam: Blind pissebedje) werd
in 1954 voor het eerst gemeld uit België. De verzamelde dieren waren allen vrouwelijk wat het niet
mogelijk maakt om de individuen tot op soort te determineren. Meer intensieve inventarisaties in de
herfst van 2015 zorgden voor verschillende nieuwe waarnemingen en de ontdekking van de eerste
mannelijke exemplaren. Meer dan 60 jaar na de eerste ontdekking kan de soort dan eindelijk bevestigd
worden voor de Belgische fauna. De soort lijkt vrij algemeen op de kleigronden in het noordwesten
van het land.
Résumé
Le cloporte Metatrichoniscoides leydigii (Weber, 1880) fut mentionné pour la première fois de
Belgique en 1954. Cependant, les spécimens récoltés à l’époque étaient tous des femelles et celles-ci
ne permettent pas de confirmer l’espèce. Lors d’inventaires intensifs réalisés en automne 2015, des
spécimens ont à nouveau été récoltés, et cette fois, la présence de mâles permet de confirmer la
présence de l’espèce sur notre territoire. Cette espèce semble être commune sur sols argileux dans le
nord-ouest du pays.
Introduction
Metatrichoniscoides leydigii (Weber, 1880) is a very elusive species of woodlouse. It is a small, white
and blind species that lives deep into the soil and therefore difficult to observe. It was first described
from the Netherlands, from where most observations still originate (BERG et al., 2008). In Belgium
only female specimens were recorded so far (POLK & VAN OYE, 1956), which cannot be identified up
to species level with absolute certainty and therefore the species could not yet been confirmed as part
of the Belgian isopod fauna. Therefore extensive inventories were done by Spinicornis, the Belgian
Land Isopod Group in autumn 2015 in search for male individuals.
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Belgian localities
Oost-Vlaanderen: Gent, Zuidpark, 11.III.1954, 3, from literature: POLK & VAN OYE (1956) – Stekene,
31UES7271, 28.IX.2015, 1, leg. & det. Pepijn Boeraeve - Gent, cemetery, 31UES5153, 18.XI.2015, 1, leg.
& det. Gert Arijs – West-Vlaanderen: Oostende, cemetery, 31UDS9274, 10.IV.2009, 1 ex, det. Koen Lock –
Kortemark, Handzame, 31UES0052, 17.X.2015, 1 ,1, leg. & det. Pepijn Boeraeve – Wielsbeke, Sint-Baafs-
Vijve, 31UES2840, 29.X.2015, 1, leg. & det. Pepijn Boeraeve – Zedelgem, 31UES1164, 30.XII.2015, 1, 1,
leg. & det. Pepijn Boeraeve – Diksmuide, Vladslo, 31UDS9453, 26.I.2016, 1, 1, leg. & det. Pepijn Boeraeve.
The species was first mentioned for Belgium by POLK & VAN OYE (1956). They collected three
specimens under stones on March 11th 1954 at Zuidpark in Gent (Oost-Vlaanderen) and assumed that
they belonged to this species, because of its occurrence in The Netherlands. However, only female
specimens were found and therefore the species could not be identified with certainty as being M.
leydigii (POLK & VAN OYE, 1956). Nevertheless, the species was reported in the checklist by
TAVERNIER & WOUTERS (1989) and later in their distribution atlas (WOUTERS et al., 2000). No other
observations were made for 55 years until a specimen was found on a cemetery in Oostende (West-
Vlaanderen) 2009 (pers.com. K. Lock). Unfortunately, the specimen got lost and the sex is unknown.
During more intensive woodlouse inventories in 2015 it was observed in Stekene (Oost-Vlaanderen),
Kortemark (West-Vlaanderen), Wielsbeke (West-Vlaanderen), Gent (Oost-Vlaanderen), Zedelgem
(West-Vlaanderen) and Diksmuide (West-Vlaanderen). The observations made in Kortemark,
Zedelgem and Diksmuide provided the first male individuals of the species in Belgium and the species
can therefore, after microscopic research, be confirmed for the Belgian fauna after more than 60 years
of its first sighting.
Identification
M. leydigii is the only species of the genus Metatrichoniscoides that occurs in Belgium, the
Netherlands (BERG et al., 2008) and Germany (ALLSPACH, 1989). In France, three species are
occurring (SÉCHET & NOËL, 2015) and in Great Britain two species are present (GREGORY, 2012),
including M. leydigii for both countries. M. leydigii is a small (2.5-4 mm), blind species of woodlouse
of that lacks pigment (Figs 1-2). The head is broader than other small trichoniscid species and very
rough with many tubercles, the uropods are broader. On the antennae, the species has conical spines
(Fig. 3A). The epimers of the first three pleonites are somewhat upturned giving the species a more
robust appearance in comparison to other trichoniscids. Only male specimens can be identified to
species level based on their genitalia (Fig. 3B-E). Notable is the endopodite of the second pleopod
which has a transparent and bulb shaped end (Fig. 3D). This characteristic is however difficult to
observe in preserved male genitalia.
Distribution and habitat
M. leydigii is a western European species, occurring in Western France, Belgium, The Netherlands and
Western Germany according to SCHMALFUSS (2003). It has been encountered in greenhouses in Czech
Republic, Sweden, Finland (SCHMALFUSS, 2003) and Great Britain (GREGORY, 2009). Recently, the
first British population in semi-natural habitat was discovered (GREGORY, 2012). This assumes that M.
leydigii is a strict Atlantic species probably native to only five countries. However, the species is only
recorded frequently from the Netherlands, from the other countries only incidental sightings are done
(BERG et al., 2008). M. leydigii is described based on type-material from the Netherlands and probably
quite common in the sea- and river clay districts (BERG et al., 2008). The species lives in the soil and
can most easily be found under stones or between plant roots that have overgrown culverts in
agricultural areas (BERG et al., 2008). Also synantropic habitat is preferred like cemeteries, gardens
and plant nurseries. They seem to prefer clay soils along rivers, small streams and ditches (BERG et al.,
2008). There are only three sightings from France of which two from caves (SÉCHET & NOËL, 2015)
and a third from the south of France in a valley (VANDEL, 1960). The North of France is however
relatively under sampled and probably with some efforts the species could be discovered in the
departments Nord and Pas-de-Calais. In Germany there are sightings from both semi-natural habitat
along the coast and synantropic habitat more inland (ALLSPACH, 1989). The sighting from Britain was
done along a river under a piece of rubble (GREGORY, 2012).
20
Fig. 1. Dorsal view of
M
etatrichoniscoides leydigii
from the Netherlands (photo: Theodoor Heijerman).
Fig. 2. Lateral view of
M
etatrichoniscoides leydigi
i
from the Netherlands (photo: Theodoor Heijerman).
Fig. 3. Metatrichoniscoides leydigii after BERG &
WIJNHOVEN (1997). A: habitus female, B: penis male,
C: first pleopod male, D: second pleopod male with
detail of the tip of the endopodit, E: right uropods.
Fig. 4. Distribution of Metatrichoniscoides leydigii in
Belgium. The square indicate the first sighting b
y
POLK & VAN OYE (1956). Diamonds are sightings
after 2009.
The Belgian sightings are concentrated in the western part of the country (Fig. 4). The habitat
corresponds largely to the Dutch sightings. Five observations were done underneath stones in roadside
verges bordering a ditch (3 obs.), channel (1 obs.) or railway (1 obs.) which corresponds largely with
the semi-natural habitat in which it is found in the Netherlands. Two observations were done on a
cemetery which corresponds to the synantropic habitat were it is also found in the Netherlands.
Discussion
M. leydigii is a very elusive species of woodlouse, hard to find and probably the reason why it has
been recorded only two times before 2015. However, more intensive woodlouse inventories in
autumn/winter 2015-2016 revealed six new localities, indicating that the species is more common than
first expected. Also extensive surveys in the Netherlands have proven that the species is probably
much more common than expected (BERG et al., 2008). Nevertheless, the species seems to have the
centre of its distribution in the Netherlands, but can now be extended towards the west of Belgium as
well. The distribution in Belgium is almost restricted to the north-west part of the country in the
provinces of West-Vlaanderen and Oost-Vlaanderen. The main habitat are lowland agricultural
landscapes on clay-soils, where it can be found by turning stones that were dug a few centimetres into
21
the soil. Inventories in this kind of habitat could be successful especially in autumn and spring time,
when the species (like other trichoniscid species) moves higher up in the soil layers when there is a
lower risk of desiccation (own observations; GREGORY, 2009). However, attention should be paid not
to confuse the species with individuals of the genus Trichoniscoides that can be found in similar
habitat and when preserved in alcohol can lose body and eye pigments.
Acknowledgements
We would like to thank Hay Wijnhoven for permission to use his drawings and Theodoor Heijerman for the
permission to use pictures of M. leydigii.
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... This mode of introduction was also supported by the most recent record from Wentworth Castle Gardens in Stainborough by Richards (2016), where it was found within the nursery area of the walled garden. In contrast, Gregory (2012) discovered a single male specimen from the bank of the River Medway in Kent; unlike the other two (clearly introduced) records, this was a semi-natural location and had habitat characteristics similar to its known natural range in the Netherlands and Belgium (Berg et al., 2008;De Smedt et al., 2016). This observation raised speculation around the native status of this species within the British Isles. ...
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-Verspreidingsatlas Nederlands landpissebedden, duizendpoten en miljoenpoten (Isopoda, Chilopoda, Diplopoda)
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BERG M.P., SOESBERGEN M., TEMPELMAN D. & WIJNHOVEN H., 2008. -Verspreidingsatlas Nederlands landpissebedden, duizendpoten en miljoenpoten (Isopoda, Chilopoda, Diplopoda). – EIS-Nederland, Leiden & Vrije Universiteit – Afdeling Dierecologie, Amsterdam.
The occurrence of two elusive woodlice, Metatrichoniscoides leydigii (Weber, 1880) and Trichoniscoides sarsi Patience 1908, In semi-natural habitat in Kent
GREGORY S., 2012. -The occurrence of two elusive woodlice, Metatrichoniscoides leydigii (Weber, 1880) and Trichoniscoides sarsi Patience 1908, In semi-natural habitat in Kent. Bulletin of the Britisch Myriapod and Isopod group 62: 37-40.
Isopoda: Oniscidea) für Deutschland. New record of Four Woodlouse Species (Isopoda: Oniscidea) in Germany
ALLSPACH A., 1989. -Neunachweise von vier Landasselarten (Isopoda: Oniscidea) für Deutschland. New record of Four Woodlouse Species (Isopoda: Oniscidea) in Germany. Stuttgarter Beiträge zur Naturkunde Serie A (Biologie) 436: 1-8.
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Distribution and bibliography of the terrestrial Isopoda (Crustacea) of Belgium. Bulletin de l'Institut royal des
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WOUTERS K., TAVERNIER J.M. & MEURISSE L., 2000. -Distribution and bibliography of the terrestrial Isopoda (Crustacea) of Belgium. Bulletin de l'Institut royal des Sciences naturelles de Belgique, Biologie, 70: 193-205.