Lithobius (Ezembius) proximus Sseliwanoff, 1878

Wytwer, Jolanta & Tajovsky, Karel, 2019, The Siberian centipede species Lithobiusproximus Sseliwanoff, 1878 (Chilopoda, Lithobiomorpha): a new member of the Polish fauna, ZooKeys 821, pp. 1-10 : 1

Lithobius (Ezembius) proximus Sseliwanoff, 1878

Taxonomical remarks.

Lithobius proximus is formally treated as belonging to the subgenus Ezembius Chamberlin, 1919 ( Farzalieva and Esyunin 2008, Nefediev et al. 2017a, b, Nefediev et al. 2018). Species included in the subgenus Ezembius are characterized by the number of their antennal articles being limited to about 20, similar to the members of the subgenus Monotarsobius Verhoeff, 1905, but they differ from them in that the tarsal articulation of the legs 1−13 is distinct, as in the subgenus Lithobius Leach, 1814 ( Eason 1974, 1976; Zapparoli and Edgecombe 2011). Therefore, it is easy to distinguish representatives of the genus Ezembius from the majority of centipedes inhabiting the litter of Central European forests, most often belonging to either subgenus Lithobius or Monotarsobius . The morphology of specimens recorded in the Wigry National Park corresponds to the characteristics given by Zalesskaja (1978) as well as Farzalieva and Esyunin (2008). They are distinguished by having elongated antennal articles and a darker brownish to brown colour head compared to the rest of the body (Figures 1, 2). Marginal ridges of tergites 9, 11 and 13 are rather rounded, but tergites 13 and 15 occur with rounded gentle posterior projections. Males have a dorsal groove on the femur and tibia (Figure 3) and often also on the first tarsal segment of the ultimate legs. Females have gonopods with simple claws (Figures 6, 7), with 2 + 2 (most common) and sometimes with 2 + 3 or 3 + 3 spurs (Figure 8). However, in our examined material, the third spur (the most inner) was very small (<one-third of the first one), a feature that distinguishes it from Lithobius (Ezembius) sibiricus Gerstfeldt, 1858, whose males, moreover, have no sexual characters on the fifteenth pair of legs ( Zalesskaja 1978, Farzalieva and Esyunin 2008). Other key features observed on the sampled specimens were also consistent with the redescription made by Farzalieva and Esyunin (2008), i.e. head with 9-10 ocelli in 3-4 rows, coxosternum with 2 + 2 sharp teeth (Figure 4), presence of the accessory apical claw on ultimate legs in both sexes (Figure 5) and the spinulation pattern on the legs.

Female specimens with 2 + 3 or 3 + 3 spurs on gonopods were treated as very rare ( Farzalieva and Esyunin 2008) or aberrant ( Nefediev et al. 2017a). Overall, in our material the ‘aberrant’ specimens accounted for 11% of all females.

Distribution.

Lithobius proximus is the only representative of the subgenus Ezembius in Poland. Ezembius was regarded as a subgenus of the genus Lithobius by Eason (1974) for the group that occurred in eastern and northern Asia. Lithobius proximus was originally described from Irkutsk by Sseliwanoff (1878). Zalesskaja (1978) designated it as a Siberian species and later ( Zalesskaja and Golovatch 1996) defined it as a centipede that inhabited the belt from the taiga to the steppe and suggested that the Volga River limited its spread to the west. This opinion was later repeated by Dyachkov (2017). Recently, this species was characterised as a widespread Siberian boreal species ( Nefediev et al. 2017a), and later it was judged as a Eurasian species widely distributed in Russia, specifically in the Altai area ranging from the taiga on the lake shore up to the mountain tundra at approximately 2200 m a.s.l. ( Nefediev et al. 2017b). Subsequently, Nefediev et al. (2018), referred to this species as an eastern European–Transsiberian temperate range species that occurred from the eastern Russian Plain (Republics of Mari El and Tatarstan, Kirov and Samara areas; i.e. respecting the Volga River line) in the west through Siberia to the Russian Far East (Maritime Province, Sakhalin and the Kuril Islands). However, Lithobius proximus was also repeatedly recorded in Ukraine, from the Kanev Nature Reserve on the Dnieper Lowland ( Chornyi and Kosyanenko 2003, Kosyanenko and Chornyi 2008) and from the 'Chernyi Les’ forest near Kirovograd on the Dnieper Upland ( Kunakh 2013). Both stands are in the forest-steppe belt, and the nearest stand in the Kanev Nature Reserve is over 750 km in a straight line from the Wigry National Park in Poland. Thus, our records represent the western most points of the entire Lithobius proximus distribution area (Figure 9).

Ecology.

The present data indicate that Lithobius proximus is neither an accessory nor an accidental species in the litter centipede community of the horn-beam forests in the Wigry National Park; rather, it is well anchored as a co-dominant species. Quantitative data on the epigeic fauna based on the extensive pitfall trapping proved that Lithobius proximus co-dominates with two other lithobiomorph centipedes. The first is the common, eurytopic species Lithobius (Lithobius) forficatus Linnaeus, 1758, with a Holarctic range of distribution, and the second is the common forest species Lithobius (Monotarsobius) curtipes (C. Koch, 1847), with a Palearctic range. Our data appear to agree with phenological observations made by Farzalieva and Esyunin (2014) in the southern taiga of the Perm Cis-Ural region, where Lithobius proximus was the most numerous species during summer. Similarly, Sergeeva (2013) recorded Lithobius proximus as the second most frequent lithobiomorph species in the valley of Irtysh River, West Siberian region. In our observations, 20-30% of all centipedes caught by trapping during the summer, and a negligible amount during the “winter” (i.e. from September to May) sampling period, were found in both sampling seasons.