On two sibling Lathys species (Araneae, Dictynidae) from northern Europe

New diagnoses for the morphologically closely related species Lathys humilis (Blackwall, 1855) and L. nielseni (Schenkel, 1932) are provided. Th ese species are most easily distinguished from one another by their abdominal patterns. Detailed illustrations are provided, and the distribution limits and habitat preferences of both species are discussed. Previous records of L. humilis from Finland refer to L. nielseni. Th e taxonomy of the genus Lathys is also briefl y discussed.


Introduction
Lathys is a relatively large genus of dictynid spiders with 38 species known exclusively from the Holarctic (Platnick 2009). Th is genus has not been revised on a large scale. Our recent studies on the morphology of the male palp (Marusik et al. 2006) revealed that members of Lathys have a highly complex palpal structure with several features unique for the family and even for the order. Th ree species of Lathys are known to occur in northern Europe: L. humilis (Blackwall, 1855), L. nielseni (Schenkel, 1932) and L. stigmatisata (Menge, 1869) (Roberts 1995;Almquist 2006). Only the fi rst two species are known from Fennoscandia (Norway, Sweden and Finland). For more than a decade following Lehtinen's (1967) revision, L. nielseni was considered a synonym of L. humilis. Th e former species, which was described from Öland Island, Sweden, was removed from synonymy by Th aler (1981) who could show distinct diff erences in the morphology of the male palp and more prominent diff erences in the shape of the female epigyne.
A recent survey of the Swedish fauna revealed that two closely related species, L. humilis and L. nielseni, occur in the southeastern region of the country (Almquist 2006). Finnish check-lists of spiders (Palmgren 1977;Koponen 2008) mention only L. humilis. During our studies of Palaearctic Lathys we realized that specimens of L. humilis from Finland diff er greatly in their abdominal patterns from specimens of the same species from Crimea, Azerbaijan and Iran. Th e Finnish specimens of L. humilis that we studied, stored in the collections of the Zoological Museums of the University of Turku and the University of Helsinki, actually belong to L. nielseni. Although the male palps in these two species are very similar, the epigynes are quite diff erent, and both species can be easily distinguished by their abdominal patterns. Th e specifi c abdominal coloration is distinct even in juveniles. Th e diff erences in patterns were illustrated by Almquist (2006), but the importance of such diff erences was not commented on or even mentioned.
Th e goal of this study is to provide detailed diagnoses for both species and to trace the distribution range of these two sibling Lathys species.

Materials and methods
Specimens were photographed using an Olympus Camedia C-5050 camera attached to an Olympus SZX12 stereomicroscope. Th e images were processed using "Com-bineZM" image stacking software. SEM-microphotographs were taken with a JEOL JSM-5200 in the Zoological Museum, University of Turku. Scales in some fi gures are missing because of the lack of special equipment and/or computer programs. All measurements are given in millimetres. Abbreviation used for the copulatory organs: Ca -apical portion of conductor; Ct tip of conductor; Co -copulatory opening; Da -dorsal tibial apophysis; Fm -margin of the epigynal fovea; Ia -intermediate tibial apophysis; Pa -patellar apophysis; Se -septum; Va -ventral tibial apophysis.

Acronyms
Lathys can be easily distinguished from other dictynids by the presence of three tibial apophyses, the long and coiled upper arm of the conductor, which totally covers the tegulum, and a screw-like terminal part of the conductor arrested by the tibial apophyses and the cymbium (Figs 13,(15)(16)(17)19).
Females of Lathys cannot be diagnosed so easily. In all Lathys species studied by us (L. stigmatisata-and L. humilis-groups) the insemination ducts make a kind of loop or coil around the copulatory opening (cf. Figs 27, 30 and fi g. 229b in Wiehle 1953). In addition, the epigynal fovea or the pair of copulatory openings are larger than or equal to the spermatheca or in some cases about two times smaller. Th e related genus Scotolathys Simon, 1884 has no loops (or coils) around the copulatory duct, and its spermatheca is much larger than its fovea (cf. Marusik et al. 2009 Colouration. Carapace in both sexes without distinct pattern. Males slightly darker than females. Abdomen with distinct pattern consisting of white guanine dots, black pigment (cardiac mark, sides, and wide posterior band). Legs with distinct annulations.
Copulatory organs. Male palp (Figs 7-9, 13-16) with patellar apophysis, tibia with three apophyses (retrolateral dorsal, retroventral and retrolateral (or intermediate) that fi x (lock) terminal part of conductor. Conductor very long with two arms. Upper arm coiled, and terminal part spine-like and slightly twisted. Epigyne as in Figs 20, 26-27 with one shallow fovea, and copulatory openings placed in apical-lateral part of fovea. Receptacula droplet-shaped. Insemination ducts short and forming one turn.
Diagnosis. Lathys humilis can be easily distinguished from the closely related L. nielseni by the abdominal pattern consisting of dark stripes and white spots formed from guanine deposits (Figs 1-3). White guanine deposits are totally absent in L. nielseni (Figs 4-6). Th e two species can also be separated on the basis of the copulatory organs. Th e epigyne of L. humilis has shorter insemination ducts turned upwards in the place where they are attached to the spermathecae. Th e females also diff er in the shape of the fovea (cf. Figs 20, 30). In L. humilis the epigynal fovea is subdivided by the septum, fovea deep with distinct margins (there is no septum and there are no distinct margins of the fovea in L. nielseni). Th e male palps of the two species are more similar than the epigynes. Th e two species can be separated by the thicker and broader patellar apophysis in L. humilis, the shape of the dorsal tibial apophysis, and the thicker and longer tip of the conductor in L. humilis.
L. humilis can be distinguished from the Japanese L. annulata, treated for a long time as a junior synonym, by its droplet-shaped spermathecae and its shorter insemination duct forming one loop only (vs. round spermathecae and insemination ducts forming several coils, cf. fi gs 10-12 in Ono 2003). Distribution. According to the Platnick's (2009) catalogue, this species has a Palaearctic (=trans-Palaearctic) distribution with several records from China (Shandong, Anhui, Shanxi and Gansu), Taiwan and Korea. Judging from the fi gures of the Chinese specimens, all records of L. humilis refer to L. nielseni or another species (males of L. annulata are unknown). Judging from the fi gures (cf. Fig. 32) the record of this species from Shandong (Hu 1984) refers to L. nielseni. Other records of L. humilis from eastern China based on males may also refer to L. nielseni or L. annulata. Th e actual species belonging of "L. humilis" from Gansu (Schenkel 1936)  Korea (Paik 1978) refers to L. maculosa (Karsch, 1879), which belongs to the Lathys stigmatisata-group. According to our studies of the Palaearctic Lathys, L. humilis seems to be distributed from western Europe to Caucasus and Mazandaran, northern Iran (see "material examined"). Th e overlapping ranges of L. humilis and L. nielseni in SW Sweden may be caused partly by misidentifi cations. Both species were found, however, in samples from Öland in the Swedish Museum of Natural History. Habitats. According to Hänggi et al. (1995), L. humilis is found in Europe especially in coniferous forests (both spruce and pine), on the forests' edges, in fi eld shrubs and hedges, and less frequently in deciduous forests. It has been collected mostly on trees, both in canopies and on stems (Hänggi et al. 1995). According to Roberts (1995), in Great Britain it occurs on bushes and trees with small, hard leaves (heather, gorse, box, yew). Harvey et al. (2002) reported this species from bushes and trees in woodland and scrub, on oak, yew, pines, gorse, etc. It may also be fairly common on ornamental evergreen and privet hedges in parks and gardens; juveniles overwinter in leaf litter, brushwood, under bark and in other similar places (Harvey et al. 2002). In Sweden the species was reported from litter in dry pine forests, from Calluna-stands and from litter in woods with oaks and on limestone (Almquist 2006).

28 29
Length of leg segments: Colouration. Carapace in both sexes without distinct pattern, although dark stripes distinguish the cephalic area from the thoracic region. Abdomen with distinct pattern consisting of brownish pigment: long median stripe with transverse arms. Legs without annulations.
Copulatory organs. Male palp (Figs 10-12, 17-19) with patellar apophysis, tibia with three apophyses (retrolateral dorsal, retroventral and retrolateral (or intermediate) that fi x (lock) terminal part of conductor. Conductor very long with two arms. Upper arm coiled, lower part spine-like and slightly twisted. Epigyne as in Figs 23, 28-32, with indistinct epigynal fovea and distinct round copulatory openings. Spermathecae egg-shaped. Insemination ducts long with each duct having a vertical and a horizontal loop. First duct turned downwards and then upwards.
Diagnosis. L. nielseni can be easily distinguished from L. humilis and L. annulata by lacking white guanine spots on the abdomen (Figs 4-6). Th e epigyne of L. nielseni resembles that of L. annulata. Th e two species can be separated by the shape of the receptacula (egg-shaped in L. nielseni and rounded in L. annulata) and the longer insemination ducts in the Japanese species. In addition to colour pattern, males of this species can be separated from the European L. humilis by the diff erent shapes of the patellar and tibial apophyses , the thinner tip of the conductor and the absence of leg annulations (cf . Figs 1, 4). Th e females of the two species can be separated by the shape of the fovea (distinct margins and septum in L. humilis, no distinct margins and septum in L. nielseni), the shape of the spermathecae and the length and the course of the insemination ducts (cf. Figs 20,23,(26)(27)(28)(29)(30).
Distribution. It seems that this species has a trans-Palaearctic range and is distributed from the UK to Shandong (China) and possibly to Taiwan. Within Europe, this species has been reported from Austria, Belorus, the Czech Republic, Great Britain, Germany, Slovakia, Sweden and Switzerland (Helsdingen 2007). In addition, L. nielseni is also known from the St. Petersburg Area and the southern Urals in Russia. Th e easternmost proven record of this species lies in the Novosibirsk Area (ca 85°E). Th e northernmost records are from Finland (where the species is often found up to 63°N) and Kuusamo, 66°10'N (Map 1). A comparison of fi gures of the epigyne (Figs 31-32) made from Finnish and Shandong specimens (identifi ed by Hu 1984 as L. humilis) leaves no doubt that the Chinese specimens belong to L. nielseni. Other records from eastern China based on males may also refer either to L. nielseni or L. annulata (known exclusively from females). Th e identity of L. humilis from Gansu (Schenkel 1936)  Habitats. Th aler (1981) reported L. nielseni from warm pine wood steppe (as high as 1500 m a.s.l.), and Buchar and Růžička (2002) mentioned that it occurs within moss and lichens in pine forests (at 400 m). In England this species occurs in moist places at ground level on heathland, under stones or among damp, dead Molinia caerulea litter between the tussocks (Harvey et al. 2002). Almquist (2006) reported the species from dune heaths. In Finland it has been collected mainly from dry habitats, among litter, moss and lichens, also on sand dunes with Elymus. It seems that this species occurs only in litter, while the sibling L. humilis inhabits bushes and trees, and is found in litter occasionally.
Discussion.Th e taxonomy of Lathys remains poorly and improperly studied in several respects. Th e limits of this genus are unclear (Lathys insulana Ono, 2003 seems to belong to Argenna or an undescribed genus; several Nearctic species appear to be distantly related to L. humilis). Scotolathys, which has long been considered a synonym of Lathys, was recently revalidated (Marusik et al. 2009). Many Lathys species remain unstudied since their original description, with many species known only from one sex. Many species appear to have been incorrectly synonymised with L. stigmatisata. Only a few species have been illustrated adequately.
One of the reasons why the genus has been studied unsatisfactorily is a lack of developed species criteria. For example, in his revision, Lehtinen (1967) paid attention to the tip of the conductor, which is very similar in many species, or the structure of the epigynal fovea (also similar in many distantly related species) (P.T. Lehtinen pers. comm.). Th e species criteria were poorly defi ned because the conformation of the male Map 1. Distribution of Lathys humilis (dot) and L. nielseni (square). A square and a circle refer to areas where both species have been found. Some dots and two squares (Germany, Switzerland) refer to state records. An open dot and square refer to a questionable record. Diamonds refer to doubtful records of L. humilis that may relate either to L. nielseni or L. annulata. Specimens from localities east of the broken line have been studied by us (except for questionable records). palp was unknown until recently. Th e fi rst detailed and correct fi gures of the Lathys male palpal tibia were published by Th aler (1981) and the structure of the bulbus was shown for the fi rst time in 2006 (Marusik et al. 2006).