﻿A new monotypic genus of cobweb spiders from the Russian Far East (Araneae, Theridiidae)

﻿Abstract A new theridiid spider, Knoflachiakurilensisgen. et sp. nov., is described from the Kuril Islands (Kunashir). The new genus belongs to the ‘Anelosimus clade (clade 24)’ of Agnarsson (2004). A pair of raised, fused setal sockets on the cheliceral promargin adjacent to the fang base was found to be another synapomorphy of all the ‘distal theridiids’ (the ‘elongated central claw clade (clade 33)’: argyrodins, ‘Anelosimus clade’ and theridiins). Knoflachiakurilensissp. nov. demonstrates a male polymorphism similar to some Anelosimus Simon, 1891 species (e.g., A.studiosus (Hentz, 1850)).


Introduction
Theridiidae, or cobweb spiders, is the fourth largest family of the order.Currently, the family includes 2542 recent species placed in 124 genera.Among species-rich families with over 1000 species, it has the highest species/genus ratio 20.5 (WSC 2023).Worldwide Theridiidae genera were considered in three publications: Levi and Levi (1962), Agnarsson (2004) and Vanuytven (2021).Theridiidae of Far East Asia are relatively well studied due to revisions and surveys of Chinese, Japanese and Korean theridiids (Zhu 1998;Yoshida 2009;Kim 2021).
Over 30 years ago, the first author collected in Kunashir Island (Kuril Islands) a large series, over 200 specimens, of brightly-coloured theridiids, which he failed to identify to genus level.Recent attempts involving SEM microscopy allow us to recognize that the species is related to Anelosimus Simon, 189, a large genus with 75 named species (WSC 2023).The genus has chiefly a Pantropical distribution with 12 species occurring in Asia, from Indonesia northward to Korea and Japan (Zhang et al. 2011: fig. 19).The specimens from Kunashir have the habitus, colouration, pattern and copulatory organs different from Anelosimus species occurring in Asia.Comparison of somatic characters and conformation of copulatory organs between species from Kunashir Island with genotype, A. eximius (Keyserling, 1884)  the conclusion that the new species should be placed in a separate new genus.The goal of this paper is to provide detailed descriptions of the species and genus and to trace the position of the new genus among Theridiidae lineages.

Material and methods
SEM images were taken on a Tescan Vega2 and a Tescan Vega3 scanning electron microscope in the Palaeontological Institute (Moscow), operated in high vacuum mode at accelerating voltages of 10-20 kV, using SE and BSE detectors.Specimens were gradually dehydrated in 100% ethanol, dried, and sputter-coated with gold-palladium.Light microscopy photographs were obtained using an Olympus Camedia E-520 camera attached to an Olympus SZX16 stereomicroscope in the Zoological Museum of the University of Turku.Digital images of different focal planes were stacked with Helicon Focus 8.1.1.All measurements are given in millimeters.The holotype will be deposited in the Zoological Museum of the Moscow State University (ZMMU) and paratypes will be shared between the ZMMU and the Zoological Institute (ZISP) in St. Petersburg.Abbreviations of leg segments: Fe -femur, Mt -metatarsus, Pa -patella, Ta -tarsus, Ti -tibia.
Epigyne -as seen by light microscope (Fig. 9D, E): epigynal plate about as long as wide, weakly sclerotized, with pair of round membranous parts (Rm) separated by thin septum; endogyne with long coiled weakly sclerotized copulatory ducts (Cd) and dumbbell-shaped receptacles (Re) standing perpendicular to epigynal plate behind Rm.As seen by SEM (Fig. 7A, B): epigyne with kind of foveae, well delimited by latero-posterior rim (Lp) and septum (Sp).Rim and septum forming guide groove (Gg) for embolus, anteriorly from septum Gg shallower, Gg forms 2 coils (about 720°) and terminates in copulatory opening (Oc).
Composition and distribution.Only the type species, K. kurilensis sp.nov., known only from the type locality (South Kurile islands, Kunashir Island: Fig. 12).The future records of this genus are surely anticipated in other Far East regions such as Hokkaido.
Diagnosis.Same as for the genus.Well differs from other Theridiidae occurring in East Asia by colouration (Fig. 1), epigyne with septum (Fig. 9D) and male palp with strongly enlarged tibia covering half of the bulb (Fig. 9A-C).Description.Male (holotype).Total length 2.4.Carapace 1.38 long, 1.08 wide; abdomen 1.45 long, 1.35 wide.Prosoma, including legs orange-reddish, legs I as dark as carapace, sternum, mouthparts, and legs II-IV lighter.Abdomen uniformly dark dorsally, venter with lighter booklung covers and area near petiolus.Palp and leg lengths as per Table 1.Variations.Total length varies from 1.9 to 2.5.At least one male has leg colouration like in females.Variations -Total length varies from 2.25 to 2.85, colour of abdomen in alcohol from almost black to grey.
Natural history.All specimens were collected in one day by sweeping bushes.The great number of specimens collected in a few hours most likely indi- cates that they may form colonies, like Anelosimus.Some specimens look like penultimate.The presence of only one subadult specimen indicates that the species is monovoltine.
Distribution.Known from the single locality in Kunashir Island (Fig. 12).Male polymorphism.Males vary in size and relative length of the first leg (cf.Fig. 1C and 1D).Larger males have a relatively longer femur I (femur I/carapace length ratio ca.1.45 in large male and 1.33 in small).Larger males have a distinct tibial and metatarsal macrosetae on legs I and II (setae standing on tegumental stump-like outgrowth

Discussion
The following characters of Knoflachia gen.nov.should be discussed in more detail, in comparison with other theridiid genera.In the naming (and the numbering) of the theridiid clades we are following Agnarsson's (2004: fig. 105) cladogram.
(1) Prosoma-abdomen stridulatory mechanism."Typically, pairs of elevated setal bases, here called stridulatory picks (SP; the term plectrum refers to such stridulatory parts in general) bordering [as a row, SPR] the pedicel on the abdomen interact with ridges on the posterior margin of the carapace (pars stridens)" (Agnarsson 2004: char. 128).This mechanism is characteristic of theridiid spiders, and the presence of SPR was stated as a synapomorphy of the theridiids minus hadrotarsines ('SPR clade, clade 50')."Although commonly present in both sexes, both the picks [...] and the ridges [...], are usually much reduced in the female, and the stridulatory role in male courtship shown for a number of species [...] can thus be presumed to be universal" (Agnarsson 2004: p. 474).The sexual dimorphism of this character in Knoflachia gen.nov. is extremely strong: SPR setal bases sharply differ in male (longitudinal and strongly keeled: Fig. 4D, E) and in female (dome-shaped, as well as other setal bases: Fig. 4F), while a ridged prosomal pars stridens is present in the male (Fig. 4A, B) and completely absent in the female (Fig. 4C).As regards the male prosomal stridulatory ridges (PSR), the two characters with two modalities may be distinguished here: (1) pars stridens separated into two patches, or continuous (Agnarsson 2004, char. 129); (2) ridges clear and deep, or fine, sometimes irregular (Agnarsson 2004, char. 128).Accordingly, every theridiid genus may be nested by its pars stridens parameters into the four-cell matrix: (  4A, B) only, as it is known.Besides, tetragonal in profile SPR setal bases vertically protruded from its medial portion setae seem to be unique in Knoflachia gen.nov.(Fig. 4D, E) (i.e., neither ectally nor mesially directed: Agnarsson 2004, chars 153, 156, 157).
(2) Size of tarsal organ: "The typical araneoid tarsal organ (all legs and palpi) is about the size of a macrosetal or trichobothrial socket, with the opening clearly smaller than the width of adjacent setae […] Some theridiids (clade 46) have enlarged tarsal organs in which the circumference is equal to or larger than adjacent setal sockets, and the opening is as large or larger than those of setal or trichobothrial sockets" (Agnarsson 2004: char. 198).The tarsal organ opening of Knoflachia gen.nov. is clearly larger than those of the setal sockets (Fig. 5E), and it belongs to the 'enlarged TO clade (clade 46)', uniting all the non-hadrotarsin and non-latrodectin theridiids.

Figure 1 .
Figure 1.General appearance of Knoflachia kurilensis sp.nov.A, B female C, F male A, F dorsal B-D lateral E ventral C, D showing the size difference of males.Scale bars: 0.5 mm (A-D, F); 0.2 mm (E).

Figure 2 .
Figure 2. Somatic characters of Knoflachia kurilensis sp.nov.A part of male tibia I, showing modified ventral seta B whole male leg I C male prosoma, dorsal D posterior part of the female abdomen, ventral, cellular setae indistinct.Scale bars: 0.2 mm.

Figure 3 .
Figure 3. Prosoma of Knoflachia kurilensis sp.nov.A male carapace and legs, lateral view B female sternum C female carapace, dorsal view D lateral margin of male carapace E female labium F cheliceral promargin of female (note fused setal socket adjacent to fang base).

Figure 4 .
Figure 4. Prosoma-abdomen stridulatory mechanism in Knoflachia kurilensis sp.nov.A posterior margin of male carapace, prosomal stridulatory ridges B the same, enlarged C posterior margin of female carapace (note absence of PSR) D male abdominal stridulatory pick row E the same, enlarged F female abdominal stridulatory pick row (note dome-like setal bases of SPR, the same as surrounding setal bases).Abbreviations: PSR -prosomal (carapace) stridulatory ridges; SPR -stridulatory pick row.

Figure 5 .
Figure 5. Knoflachia kurilensis sp.nov.: leg setae, tarsal organ and trichobothria A ventral macrosetae of male metatarsus I B tarsus IV comb of female C same, enlarged D tarsal organ of female leg II E same, enlarged F trichobothrial bases of male palpal tibia.

Figure 6 .
Figure 6.Knoflachia kurilensis sp.nov.: tarsal claws A tarsus IV of male B tarsus IV of female C tarsus II of female D female palpal claw.

Table 1 .
Palp and leg lengths of the male holotype.

Table 2 .
Palp and leg lengths for female allotype.