Catching of spiders in shallow subterranean habitats in the Czech Republic

Spiders occurring in soils and fissured rocks were investigated using pipe traps. Four microphthalmic species, namely Hahnia microphthalma, Porrhomma egeria, P. microps and P. cambridgei were collected. Hahnia microphthalma is reported from the Czech Republic for the first time. The importance of collecting material by complex pipe traps (consisting of a perforated pipe and a set of removable cups) to record the depth distribution of spiders in subterranean habitats is stressed. The importance of the soil and fissure network formed by sandy marlite bedrock and of alluvial soils for the life of subterranean spiders is documented.

For humans, caves are more accessible than other subterranean habitats.Much of what we know about subterranean biology comes from the study of caves, partly because of the adventure and excitement of visiting and exploring caves, which are certainly more exciting than visiting, for example, talus slopes (Culver & Pipan 2009).Terrestrial shallow subterranean habitats are formed in soil, rock mantle formed in bare and forest scree, slope and alluvial sediments and in fissured rock and cave entrances (Culver & Pipan 2014).A depth of about 10 m represents the natural border between shallow and deep subterranean habitats (Novak et al. 2012, Růžička et al. 2013).Our knowledge concerning invertebrates that live only several metres under the surface is very limited.
Many subterranean invertebrates display similar morphologies that have evolved convergently under similar selective pressures imposed by the subterranean environment.Subterranean spiders show typical morphological changes known as troglomorphisms: depigmentation, microphthalmy and lengthening of the legs (Culver & Pipan 2009).
Arachnological research into shallow subterranean habitats has a long tradition in the Czech Republic.Independently of Juberthie & Delay (1981), Růžička (1982) started to investigate invertebrates living in talus slopes using board traps.Numerous surprising findings have been reported since, including five taxa new to science, and twelve species of arthropods new to the Czech Republic (Růžička & Klimeš 2005).Wubanoides uralensis (Pakhorukov, 1981) (respectively Wuba noides uralensis lithodytes Schikora, 2004), was recorded for the first time in Europe and several troglomorphic populations/ taxa have been described (Růžička 1988a(Růžička , 1998(Růžička , 2011)).His research has documented that freezing talus slopes represent a classic example of a palaeorefugium that significantly contributes to the protection and maintenance of regional landscape biodiversity (Růžička et al. 2012).
The main component of traps used by López & Oromí (2010) for catching invertebrates in shallow subterranean habitats on the Canary Islands is a 75 cm long plastic pipe with an inner diameter of 11 cm.Many small holes (5-7 mm in diameter) are drilled along its surface, and a bottle containing preservation fluid (and bait) is lowered inside on a nylon cord.The pipes are installed vertically into holes in a suitable terrain.This kind of trap is a modification of a similar pipe used by Gers (1992).Barranco et al. (2013) 2012) studied the distribution of invertebrates in limestone scree slopes.The design of perforation varies from a horizontal line of holes, to a network of holes up to horizontal cuttings accompanied by holes (Fig. 1a-c).The aim of this present study was to test the performance of pipe traps in soils and crevice systems.

Material and methods
Sampling.Six pipe traps (one per site) were deployed from 2013 to 2015, and were emptied twice a year.The plastic pipes have an inner diameter of 7 cm, and are perforated with a system of oblique cuts 5 mm wide (Fig. 1d).This design has been registered at the Czech Industrial Property Office under No. 36420.Plastic cups were mounted onto a metal-thread rod at 10 cm distances and contained a mixture of 7 % formalin and 5 % glycerol, plus a few drops of detergent (Růžička 1988b).In the final version, we used plastic or brass components to avoid damage to material caused by rust.We installed these traps in excavated trenches in sandy marlite terrains, or in boreholes (15 cm in diameter) in lowland forests, the deepest reaching 160 cm below the surface.The free space around the trap was filled by excavated material or -in the case of boreholes -by a mixture of excavated material and artificial rubble (Keramzit) or starch-based packing peanuts.

Spiders
In total, we captured 335 spider specimens belonging to 32 species (Appendix): 155 spiders belonging to 20 species at site SM-1 (Tab.1), 44 belonging to 10 species at site SM-2 (Tab.2), 118 belonging to 12 species at site SM-3 (Tab.3), 7 belonging to 3 species at site AS-1 (Tab.4), 11 belonging to 3 species at site AS-2 (Tab.5) and 7 belonging to 3 species at site AS-3 (Tab.6).Spiders were recorded down to a depth of 120 cm.Cicurina cicur was the most abundant species.Species that were clearly tied to surface habitats (e.g., Agroeca cuprea) were usually recorded only a few tens of centimetres deep.Some individual records can be considered as accidental, e.g. the record of Linyphia hortensis at a depth of 110 cm, due to the fact that it is a typical shrub layer inhabitant (Buchar & Růžička 2002).Cicurina cicur, Mioxena blanda, Palliduphantes pallidus, P. alutacius and Syedra myrmicarum were depigmented with fully developed eyes.Four species were depigmented with reduced eyes and were clearly adapted to life in subterranean habitats.These species represent objects of our special interest.

Hahnia microphthalma
Material: Jenišovice-Mravín (SM-2), 25 October 2013-18 April 2014 1(; 28 April-29 September 2015, 1(.This species is reported for the first time from the CZECH REPUBLIC. Posterior median eyes reduced (Fig. 3a).Szita et al. (1998) andHänggi &Stäubli (2012) found various stages of eye reduction in their material, and also differences in the form of the translucent copulatory ducts.The picture of the copulatory ducts of the epigyne of our specimens is in agreement with that of the type specimen (Fig. 3b; cf.Snazell & Duffey 1980: Fig. 3).Snazell & Duffey (1980) described the species according to two records from Great Britain.Hänggi & Stäubli (2012) summarized other records: three in Germany, one in Switzerland, and one in Hungary (Fig. 4).British specimens were collected in chalk grassland and in a field with a clay soil over-Tab.1: The species assemblage at SM-1.The number of males, females and juveniles ())/((/juv.[if determinable]) and the depth range (in cm) are shown.The species considered microphthalmic are shown in bold.
All previous specimens were collected on the surface by pitfall traps, photoeclectors or by sweeping.Snazell & Duffey (1980) conclude that some of the characteristics of the spider suggest a subterranean habitat.We document for the first time that H. microphthalma inhabits the soil at a depth of about 50-70 cm.(Thaler et al. 2003).

Porrhomma cambridgei
We and Růžička et al. (2011, sub.P. aff.myops) captured this species in sandy marlite terrain and in alluvial soils at a depth of 35-120 cm.Thaler et al. (2003) collected this species on tree bark in the Bohemian Karst and we also obtained several specimens from conglomerate terrain and from karst caves.
Porrhomma microcavense Wunderlich, 1990 was reported from a sandstone landscape for the first time in the Czech Republic (Buchar & Růžička 2002).However, in detail, it was recorded above a sandy marlite layer.Furthermore slightly microphthalmic specimens of Oreonetides quadridentatus (Wunderlich, 1972) were captured by Laška et al. (2011; sub Maro sp.) at a depth of 45 and 65 cm in clay soil on sandy marlite bedrock, together with Porrhomma microps.Alluvial soils.We collected P. cambridgei and P. microps in alluvial soil/sand in three different localities in lowland forests near a river.In the same habitat, Růžička et al. (2011) collected these two species together.Together with H. microphthal ma, these two species can be considered soil spiders.

Concluding remarks
The importance of shallow subterranean habitats for the evolution of subterranean life is well known (Růžička 1999, Giachino & Vailati 2010, Růžička et al. 2013, Culver & Pipan Tab.6: The species assemblage at site AS-3

Species
))/(( Zangherella relicta (Kratochvíl, 1935), described from a cave in Montenegro, was recorded, which represents the first record of the family Anapidae in Bulgaria.Gilgado et al. (2015) collected the troglomorphic millipede Typhlopsychrosoma ba eticaense (Mauriés, 2013), known from caves, in mountain screes and concluded that some subterranean species might have surprisingly wide distribution areas, and that study of shallow subterranean habitats will surely improve our poor knowledge on subterranean biodiversity.There is a wide spectrum of sedimentary rocks containing variable amounts of clay and silt designated as marl or marlite.Their properties depend on mineralogical composition and diagenesis.In the Alicante region (Spain), the marl offers no suitable insterstices for a subterranean fauna, and marl layers constitute physical barriers to the movement of subterranean animals (Ortuño et al. 2013, Gilgado et al. 2015).On the other hand, in the Czech Republic, the indurated sandy marlite forms a fissure network.This fissure network, together with soils originating from this bedrock, constitutes a subterranean habitat that seems to be very suitable for the subterranean fauna, according to our findings.
In subterranean biology, there is a common idea that alluvial plains are barriers to subterranean faunas, and that they do not have suitable spaces (Uéno 1987).However, this depends on the size of the sand and gravel grains.Christian (1998) recorded a subterranean palpigrade Eukoenenia austri aca (Hansen, 1926) (usually found in caves) in the bottom substrate of the tombs of St. Stephen's Cathedral in Vienna.These catacombs were dug down to the Pleistocene gravel of the Danube river.Gilgado & Ortuño (2015) recorded a subterranean zygentomid Coletinia maggii (Grassi, 1887) (usually found in surface habitats, ant nests and caves) in a subsoil gravel layer in an alluvial plain in northern Spain.We collected subterranean spiders in three different alluvial plains.These findings suggest the possibility that alluvial deposits might represent 'connectors' between other subterranean habitats, at least for some subterranean animals.Moreover, in the locality AS-1, we collected not only the subterranean spider Porrhom ma cambridgei at a depth of 30-80 cm, but also a pale subterranean Niphargus sp. at a depth of 0-90 cm.Crustaceans thus migrated into soil horizons from shallow aquatic interstitial habitats at the time of flooding.
The modified space around the pipe can represent an artificial corridor through which invertebrates can migrate in a vertical direction.Nevertheless, the vertical distributions of spiders are clearly species-specific as also documented by Laška et al. (2011).In both cases of the common occurrence of P. microps and P. cambridgei (our site SM-2 and Růžička et al. 2011), the smaller species P. cambridgei occupies deeper soil horizons.
On the other hand, the soil structure is destroyed during installation of the traps, and fine crevices are closed.The reconstruction of the network of voids can take several years, as we infer by the catching of the first adults of P. egeria after two years of investigation.
Finally, we would like to recommend the use of complex pipe traps, which enables precise documentation of the depth distribution of species.We would like to emphasize that to document the occurrence of troglomorphic invertebrates, data on the subterranean habitat (not only data on surface habitat, e.g.plant associations) are important.
, Ortuño et al. (2013) and Jiménez-Valverde et al. (2015) used such traps to investigate invertebrates in stony slopes and river deposits in continental Spain; Nitzu et al. (2014) used a similar trap in Romania.Schlick-Steiner & Steiner (2000) constructed a trap consisting of a perforated pipe and a set of removable plastic cups situated on a central-thread metal axis.Through this arrangement, the cups collect animals entering the tube through holes at particular depths.Using these complex pipe traps (with a length of 95 cm), Laška et al. (2011) studied the distribution of spiders in soil profiles and Rendoš et al. (