A review of the Holarctic genus Tmeticus Menge, 1868 (Araneae, Linyphiidae), with a description of a new genus

Abstract Eight species attributed to Tmeticus are reviewed; five are redescribed and illustrated: Tmeticus affinis (Blackwall, 1885), Tmeticus bipunctis (Bösenberg & Strand, 1906), Tmeticus nigriceps Kulczyński, 1916, Tmeticus ornatus (Emerton, 1914) and Tmeticus tolli Kulczyński, 1908. The new genus, Paratmeticus gen. n. is erected for Tmeticus bipunctis, and a new combination is established: Paratmeticus bipunctis (Bösenberg & Strand, 1906), comb. n. Three species names: Gongylidium vile Kulczyński, 1885, syn. n., Tmeticus difficilis Kulczyński, 1926, syn. n. and Tmeticus dubius Kulczyński, 1926, syn. n., are synonymized with Tmeticus tolli Kulczyński, 1908. Although Gongylidium vile has date priority over Tmeticus tolli it is synonymized because of the lack of usage. Three species from Japan attributed to Tmeticus: Tmeticus neserigonoides Saito & Ono, 2001, Tmeticus nigerrimus Saito & Ono, 2001 and Tmeticus vulcanicus Saito & Ono, 2001 are not related to Tmeticus affinis, the type species of the genus, and their affinities remain unclear. The male of Tmeticus nigriceps is described for the first time.


Introduction
Tmeticus is a small Erigoninae genus with nine species restricted to the Holarctic Region (Platnick 2010). Members of this genus can be easily recognized by their elongate male palp with a small bulbus and a ventral tooth on the patella. Only the type species of the genus, T. affi nis (Blackwall, 1855), occurs both in the Palaearctic and Nearctic Regions. One species, T. ornatus (Emerton, 1914), is restricted to the Nearctic Region. All other species have been recorded from Asia. Th e highest species diversity of the genus is in Japan, as a result of three recently described species.
While studying the Siberian and Far Eastern Linyphiidae, we encountered certain diffi culties in identifying Tmeticus species. Only two of the four species occurring in northern Asia, T. affi nis (Blackwall, 1885) and T. tolli Kulczyński, 1908, were properly illustrated. Th us, the main purposes of this study are to provide diagnostic illustrations for each Asian species and to describe a new genus.

Material and methods
Pictures of the general appearance and copulatory organs were made using an Olympus SZX16 stereomicroscope, with an Olympus E-520 camera, and prepared using CombineZM software. Photographs were taken in dishes of diff erent sizes with paraffi n in the bottom. Diff erent sized holes were made in the bottom to retain the specimens in the desired position. Scanning electron micrographs were made using a SEM JEOL JSM-5200 scanning microscope. SEM and digital photographs were made in the Zoological Museum, University of Turku. Th e terminology of the copulatory organs follows Hormiga (2000). Th e smallest and biggest specimens are reported, all measurements are in millimetres.

Abbreviations IBPN
Institute for Biological Problems of the North, Russian Academy of Sciences, Magadan (curator Yu.M. Marusik).
Diagnosis. Males of this genus are easily recognized by possessing a mastidion (large tooth on frontal part of chelicera) and by their elongate palp with patella longer than cymbium, ventral terminal tooth on patella, and thin bulbus (as wide as terminal part of tibia). Females are recognized by their fl at epigyne without a cavity. Males may be confused only with the trans-Palaearctic Hylyphantes graminicola (Sundevall, 1830) because it also has a mastidion and a patellar tooth. However, the males of Hylyphantes have shorter palp, undivided embolic division and screw-like embolus.
Th e females of Tmeticus may be confused with those of several genera, such as Oedothorax Bertkau, 1883 or with Donacochara speciosa (Th orell, 1875). However, Oedothorax females have a diff erent colour pattern, and D. speciosa is notably larger.
On the basis of the present study, we conclude that Tmeticus encompasses four species: T. affi nis, T. nigriceps, T. ornatus and T. tolli. A new genus has been erected for T. bipunctis. Tmeticus neserigonoides might be correctly placed in this genus, but as we failed to re-examine its specimens, we treat it as incertae sedis (see below). Two other Japanese species belong elsewhere, but their correct assignments require further study.
Comments. Tmeticus is unusual in the Erigoninae because all its species can be recognized by their carapace colour pattern. Th ree sibling species: T. nigriceps, T. ornatus and T. tolli cannot be recognized by their embolic division, but the females of these species have distinctly diff erent epigynes.
Interrelationships. T. affi nis diff ers from the three other species by the shape of the paracymbium, the straight embolus and the high protegulum with papillae. It also possesses a diff erent type of the tibial apophysis, not originating at the terminal edge of the tibia as in other Erigoninae and other Tmeticus, but slightly aside of the edge.

Relationships.
In general appearance, male palp structure and cheliceral dentition, the members of this genus are similar to Hylyphantes graminicola, but the latter has a diff erent type of embolic division and epigyne. When Wiehle (1956) described Donacochara speciosa (Th orell, 1875) he compared it with T. affi nis. Both species have a long palp, small bulbus, and the chelicera of the male has a mastidion. Th e embolic division in both species is rather similar, but the radical process and the embolus proper occupy diff erent positions.
Judging from the drawings (Figs 35.110, 35.111 in Draney and Buckle 2005), Tmeticus can be related to the Nearctic Nanavia monticola Chamberlin & Ivie, 1933. Th e latter species seems to have been mistakenly considered a synonym of Leptorhoptrum robustum (Westring, 1851) (see Platnick 2010). Both genera and species were synonymized by Eskov and Marusik (1994) on the basis of a comparison of L. robustum and the poor fi gures of N. monticola. N. monticola has a very long palpal tibia, and the paracymbium and embolic division are very similar to those of T. affi nis. Th e relationships of the two genera and taxonomic status of Nanavia Chamberlin & Ivie, 1933 are outside the scope of this study and will be considered elsewhere.

Key to Tmeticus species
Th e males of T. nigriceps and T. ornatus cannot be distinguished.

Tmeticus ornatus
Description. ♂ 2.5-3.3, ♀ 2.8-35. TmI 0.73-0.78. Carapace orange with darker cephalic region. Abdomen dark. Palp as in 51,54. Epigyne as in Figs 17,[47][48] Distribution. Th is species has a trans-Nearctic distribution, recorded from British Columbia to Quebec and south to New York (Buckle et al. 2001). It does not occur north of 55°N and has a more southern distribution in comparison to the Palaearctic T. affi nis, T. tolli and T. nigriceps.

Species Incertae Sedis
Th e three species from Japan assigned to Tmeticus remain unstudied and belong elsewhere (see 'Comments' below).
Comments. Judging from the available fi gures, this species might belong in Tmeticus. Th e male has a long palp with a patellar tooth. However, the chelicera appears to lack a mastidion and the tibial apophyses are absent. Figures of the male palp are unclear, TmI index (0.59) is lower than in Tmeticus species (>0.63).

Comments.
Th is species is clearly not related to T. affi nis or other members of the genus due to the short palpal patella lacking a tooth in the male, embolic division of a diff erent shape, the relatively long tibial apophysis, lack of a mastidion, epigyne with a septum and some other additional characters. Th e correct generic placement remains unclear.

Comments.
Th is species is clearly not related to T. affi nis or other members of the genus due to the short palpal patella lacking a tooth in the male, embolic division of a diff erent shape (anterior radical process absent), and some other characters. Th e correct generic placement remains unclear.
Diagnosis. Th e new genus is easily distinguished from the similar Tmeticus by lacking distinct tibial apophyses, and in having the papillate tegular sac larger than the protegulum, a slightly twisted embolic division, a sharply pointed embolic membrane and a large distal suprategular apophysis, longer than the embolic division. In contrast to Tmeticus, the median plate of the epigyne in the new genus is widest in the anterior region, rather than in the posterior region.
Description. Medium-sized erigonine spiders. Uniformly coloured, male carapace without modifi cations, male chelicera with mastidion, inner row with 4 inner teeth and 5 outer teeth (all smaller than inner teeth). TmI 0.63-0.65. Male palp elongate, with patella as long as tibia, tibia lacks apophyses, distal suprategular apophysis longer than embolic division; embolic division slightly twisted with two arms: anterior radical process and embolus proper; embolus parallel to process with lamellate basal process; epigyne without cavity, median plate widest anteriorly.
Composition. Th e type species only.