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21 October 2021 On the Peruvian Erigone palustris Millidge, 1991, with notes on the psychrophila-species group (Arachnida: Araneae)
Andrei V. Tanasevitch
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Abstract

The Peruvian high-altitude spider species Erigone palustris , a member of the psychrophilaspecies group, is redescribed and illustrated. This species is very similar to the northern European hypoarcto-boreal E. svenssoni , different only in a few minor details of the male palp. A list of the psychrophila-species group is presented and its biogeography is discussed.

INTRODUCTION

At present the Erigone psychrophila species group (sensu Crosby & Bishop, 1928) includes at least 23 species (see Table 1) which mainly occur in the Northern Hemisphere, mostly in the tundra, boreal and montane regions of the Holarctic. Only two species, E. clavipalpis Millidge, 1991 and E. palustris Millidge, 1991, live in the Southern Hemisphere, in the highlands of the Peruvian Cordilleras (Millidge, 1991). Four conspicuous species in this group share a characteristically long and sabre-shaped process on the ventral surface of the male palpal tibia (SP in Figs 5, 7): E. svenssoni Holm, 1975, known from northern Europe, E. hydrophytae Ivie & Barrows, 1935 and E. uintana Chamberlin & Ivie, 1935, described from Florida and Uta, U.S.A., respectively, and E. palustris Millidge, 1991, from Peru.

Quite unexpectedly, a male labeled as E. svenssoni was recently found in the spider collection of the Muséum d'histoire naturelle de Genève, Switzerland. This species is known to occur in the taiga and tundra belts of northern Europe, however the specimen examined was collected in the highlands of the Cordilleras of Peru. Such a disjunction would be so unusual that I decided to carefully check if the identification of that male is correct, since at first glance it truly looked like representing the northern European species.

MATERIAL AND METHODS

This paper is based on spider material kept in the Muséum d'histoire naturelle de Genève, Switzerland (MHNG) and in the personal collection of Andrei Tanasevitch, Moscow (CAT). Specimens preserved in 70% ethanol were studied using a MBS-9 stereomicroscope. A Levenhuk C-800 digital camera was used for taking photos. Leg chaetotaxy is presented in a formula, e.g., 2.2.2.1, which refers to the number of dorsal spines on tibiae I-IV. The sequence of leg segment measurements is as follows: femur + patella + tibia + metatarsus + tarsus. All measurements are given in mm. Scale lines in the figures correspond to 0.1 mm unless indicated otherwise. Figure numbers are given above the corresponding scale lines, the length they represent is given below them. The terminology of copulatory organs mainly follows that of Merrett (1963) and that of authors mentioned in the abbreviations below.

Abbreviations

a.s.l.

above sea level

DSA

distal suprategular apophysis sensu Hormiga (1994)

E

embolus

EM

embolic membrane sensu Tanasevitch (2017), not sensu Hormiga (1994, 2000)

EP

embolus proper sensu Saaristo (1971)

MRA

median radical apophysis (= median tooth sensu Crosby & Bishop, 1928)

MRT

mesal radical tooth (= mesal tooth sensu Crosby & Bishop, 1928)

PN

posterior notch of radix

PRA

posterior radical apophysis (= posterior tooth sensu Crosby & Bishop, 1928)

SP

sabre-shaped process

TmI

position of trichobothrium on metatarsus I.

Table 1.

Composition and distribution of the Erigone psychrophila-species group.

img-z2-4_375.gif

Figs 1-4.

Photographs of a male of Erigone palustris Millidge, 1991 deposited in the MHNG. (1) Habitus, dorsal view. (2-4) Prosoma, dorsal, ventral and frontal views, respectively.

img-z2-5_375.jpg

TAXONOMY

Erigone palustris Millidge, 1991
Figs 1-6

  • Material: MHNG; 1 male, labeled as Erigone svenssoni Holm; PERU, Junin Department, La Oroya, Pachacayo, 3700-3750 m ü NN (= a.s.l.); 22.XII.1978; leg. and det. S. Heimer.

  • Comparative material examined: Erigone svenssoni Holm, 1975: MHNG (collection of S. Heimer); 1 male (see Figs 7-8), 2 females; SWEDEN, Swedish Lapland, Stordalen, mire; 14.-23.VI.1979; leg. Å. Holm. – CAT; 1 male, 6 females; RUSSIA, environs of Vorkuta, near Vorgashor, sedge fen on lake bank; 5.XI.1983; leg. A. Tanasevitch. – CAT; 2 males, 1 female, same locality; 4.IX.1984; leg. A. Tanasevitch.

  • Description: Male. Total length 1.88. Carapace (Figs 1-2, 4) 0.90 long, 0.68 wide, reddish brown, its cephalic part arched. Lateral edges of carapace with irregular sharp teeth of different sizes. Chelicerae 0.50 long, retrolateral-frontal side with a row of small teeth, mastidion absent. Promargin of cheliceral groove with one small and two large teeth, retromargin with two small teeth. Legs yellow. Leg I 2.24 long (0.62 + 0.23 + 0.54 + 0.47 + 0.38), IV, 2.24 long (0.62 + 0.23 + 0.56 + 0.48 + 0.35). Chaetotaxy 2.2.2.1, spines about as long as diameter of corresponding leg segment. Metatarsus IV without trichobothrium. TmI 0.42. Palp (Figs 5-6): Patella long and slender, with a large, conical ventroapical apophysis. Tibia elongated, with an anterior concavity typical for the psychrophila-species group, and with a characteristic ventral sabre-shaped process. Distal suprategular apophysis elongated, rounded distally, strongly sclerotized. Embolic division typical for the group: mesal radical tooth conical, pointed; median radical apophysis not expanded distally; embolic membrane bipartite, transparent. Posterior notch of radix very small, resulting in a short posterior radical apophysis. Abdomen 1.00 long, 0.68 wide, pale grey.

  • Distribution: The species is known only from the highlands of the Peruvian Cordilleras at 2530-3850 m a.s.l. (Millidge, 1991).

  • Remarks: The spider collection of the MHNG has a male labeled as Erigone svenssoni Holm, 1975, which has been collected by Stefan Heimer (Dresden) in the highlands of the Peruvian Cordilleras in 1979. In 1991 A.F. Millidge described E. palustris on the basis of several males and females from high altitudes (2530-3850 m a.s.l.) from the same mountain region of Peru (Millidge, 1991). In the diagnosis of this species Millidge did not mention that it belongs to the psychrophila-species group, and only compared it with a few Erigone species known from South America. On the other hand, Heimer was not far from the truth, having identified the male he collected in Peru as the Swedish Laplandic E. svenssoni. Erigone svenssoni was originally described from Sweden (Holm, 1975) and later also recorded from the northern part of the Russian Plain [Karelia (Byzova et al., 1986)], from the Polar Urals (Esyunin et al., 1995), and from the Bolshezemelskaya tundra (Tanasevitch & Koponen, 2007). Both species belong to the psychrophilaspecies group, and are really very similar to each other. The male from high-altitudes of Peru, belonging to E. palustris, differs from that of the northern European hypoarcto-boreal E. svenssoni by a few details of the embolic division, i.e. the shorter median radical apophysis with a more or less even apical edge (see MRA in Figs 6, 8), the smaller posterior notch of the radix, and the smaller posterior radical apophysis (see PN and PRA in Figs 6, 8). The epigynes of both species are rather different in the shape of the posterior median plate (triangular in E. svenssoni vs trapezium-shape in E. palustris) and of the receptacles [much large in the European species (Holm, 1975: fig. 8; cf. Millidge, 1991: fig. 551)].

  • Figs 5-8.

    Details of the left palp of a male of Erigone palustris Millidge, 1991 (5-6) and of a E. svenssoni Holm, 1975 male from Swedish Lapland (7-8) deposited in the MHNG. (5, 7) Palp, retrolateral view. (6, 8) Embolic division, mesal (= prolateral) view.

    img-z3-10_375.jpg

    ACKNOWLEDGEMENTS

    I am deeply grateful to Peter Schwendinger (MHNG) for providing the opportunity to work on the MHNG spider collections and for editing this paper. Thanks also go to Dragomir Dimitrov (National Museum of Natural History, Sofia; currently at the University of Barcelona) who kindly reviewed the manuscript.

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    Andrei V. Tanasevitch "On the Peruvian Erigone palustris Millidge, 1991, with notes on the psychrophila-species group (Arachnida: Araneae)," Revue suisse de Zoologie 128(2), 375-379, (21 October 2021). https://doi.org/10.35929/RSZ.0051
    Accepted: 8 June 2021; Published: 21 October 2021
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    Erigoninae
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