Taxonomic notes on Stemmops O. Pickard-Cambridge, 1894 (Araneae, Theridiidae) of China

Abstract Background The theridiid spider genus Stemmops O. Pickard-Cambridge, 1894 includes 27 extant species and is distributed in America (23 spp.) and Asia (4 spp.). Three species, S.forcipus Zhu, 1998 (♂♀), S.nigrabdomenus Zhu, 1998 (♂) and S.nipponicus Yaginuma, 1969 (♂♀), are currently known from China. New information Two new species of Stemmops are described from China: S.atratus sp. n. (♀, Jiangsu, Zhejiang) and S.lini sp. n. (♂♀, Fujian, Zhejiang). In addition, the previously unknown female of S.nigrabdomenus Zhu, 1998 is described. Photos and morphological descriptions are provided.


Introduction
The comb-footed spider family Theridiidae Sundevall, 1833 comprises 124 genera and 2541 known extant species worldwide (World Spider Catalog 2023).Stemmops Gerstaecker, 1873 was described with S. bicolor O. Pickard-Cambridge, 1894 from Teapa, Tabasco, Mexico as its type species.This genus can be separated from other related genera by: 1) chelicerae lacking tooth, 2) large eyes relatively close to one another, 3) short, stout legs, 4) the presence of only two spermathecae and 5) the colulus replaced by two setae (Levi 1955).
Stemmops currently comprises 27 extant species, distributed in America (23 spp.) and Asia (4 spp.).Although the Chinese spider taxonomists have published a large number of papers during the 21 century, due to the rich biodiversity of the country, many groups remain poorly studied (Li 2020, Li et al. 2021, Yao et al. 2021, Lu et al. 2022, Zhao et al. 2022).Regarding Stemmops, Chen and Zhang (1991) provided the first data on this genus from China, by reporting S. nipponicus Yaginuma, 1969 from Zhejiang.However, the figures in that article are extremely schematic and the specimens are lost; therefore, it is impossible to determine whether the species identification is correct.Zhu (1998) described two species and, since then, the study of Stemmops in China has remained at the stage of reporting new distribution data.Therefore, three Stemmops species are currently known from China: S. forcipus Zhu, 1998, S. nigrabdomenus Zhu, 1998 andS. nipponicus (Chen andZhang 1991, Zhu 1998).
During the examination of Chinese Stemmops specimens, we found two new species, as well as the unknown female of S. nigrabdomenus from Guangxi, all of which are described and illustrated in this paper.

Materials and methods
All specimens are preserved in 80% ethanol.The epigynes were cleared in trypsin enzyme solution to dissolve non-chitinous tissues.Specimens were examined under a Leica M205C stereomicroscope and photographed using an Olympus C7070 zoom digital camera (7.1 megapixels).Photos of the live specimens were taken with a Sony A7RIV digital camera equipped with a Sony FE 90 mm Goss lens.Photos were stacked with Helicon Focus® (Version 7.6.1)or Zerene Stacker® (Version 1.04) and processed in Adobe Photoshop CC2022®.The distribution map was generated with ArcGIS v.10.2 (ESRI Inc.).
All measurements are in millimetres (mm) and were obtained with an Olympus SZX16 stereomicroscope with a Zongyuan CCD industrial camera.All measurements of body st lengths do not include the chelicerae.Eye sizes are measured as the maximum diameter from either the dorsal or frontal view.Leg measurements are given as follows: total length (femur, patella+tibia, metatarsus, tarsus).The terminology used in the text and figures follows Agnarsson (2004)    Colouration (Fig. 1a, Fig. 10a).Carapace dark-brown, covered with long sparse brown setae, eyes with black rings.Endites and labium green-brown.Sternum green-brown.Legs orange-brown, covered with sparse setae, more distinct on metatarsi and tarsi.Opisthosoma with two large white spots anteriorly and posteriorly, three pairs of small white symmetrical spots along the mid-line and a pair of white spots laterally, slightly larger than the small white spot in the middle.Spinnerets black.
Epigyne (Fig. 2A and B).Epigynal plate almost as long as wide, with hood anteriorly, hood almost six times wider than long.Copulatory openings located on posterior portion of epigyne.First half of copulatory ducts slightly curved and second half coils around the middle of the spermathecae for four turns.Spermathecae kidney-shaped.Fertilisation ducts kidney-shaped. Male.Unknown.

Diagnosis
The female of this new species is similar to that of S. nipponicus Yaginuma, 1969 by the split atrium (Fig. 2A).However, it can be distinguished by the presence of hood (Fig. 2A) (vs.absent) and the copulatory ducts coiled four times around the spermathecae (Fig. 2B) (vs.once in S. nipponicus).Furthermore, it differs by its habitus: S. atratus sp.n. lacks obscure yellow spots on the lateral view of opisthosoma (Fig. 1a, Fig. 10a Right) [vs.present in S. nipponicus, Yaginuma (1969) (Fig. 1d)].

Etymology
The specific epithet is derived from the Latin word ātrātus, meaning darkened, referring to the colour of the new species.

Biology
All specimens were collected under stones.

Notes
The dark venter of opisthosoma and epigynal hood indicate that the illustrated female of S. nipponicus in Jin ( 2018) is misidentified.Herein, we determine this species as S. atratus sp.n.
Compared species and material examined.Palp (Fig. 3A, B, Fig. 4A-E).Patella almost as long as tibia.Cymbium almost as long as wide.Cymbium covered with sparse setae.Subtegulum on the lateral posterior side of the bulb, half encasing tegulum.Sperm duct S-shaped, the first bend obscured by embolus, not obvious, the second bend three times as wide as the diameter of the sperm duct.Median apophysis (Fig. 4D) hidden behind the conductor and tip with a hood.Theridiid tegular apophysis (Fig. 4B) divided into two parts by a translucent membrane: anterior part slightly curved, sickle-shaped, posterior almost quadrilateral.Conductor (Fig. 4C) tip pincer-shaped, located posterior to embolic basal apophysis.Embolic basal process (Fig. 4C) with two parts: embolic basal apophysis black with sharp end and folds, embolic basal flat extension semi-circular, flaky and transparent.Embolus (Fig. 4E) falciform, with spoon-shaped embolic terminal apophysis, connected by a membrane.Colouration (Fig. 10b Right).Similar to that of male, except darker.
Epigyne (Fig. 5A, B).Epigynal plate almost as long as wide, with a weakly-developed hood anteriorly.Copulatory openings situated on posterior portion of epigyne.

Etymology
The species is named after Lin Zexu (1785-1850), a famous historical person born in Fujian who fought against imperialist aggression.

Biology
All specimens were collected under stones.

Notes
The presence of embolic basal apophysis and embolic basal flat extension and the spoon-shaped embolic terminal apophysis show the male of S. nipponicus in Jin ( 2018) is misidentified.Herein, we treat the male as S. lini sp.n.
Compared species and material examined.Epigyne (Fig. 9A, B).Epigynal plate longer than wide, almost oval, with a pair of triangular hoods posteriorly.Septum emerges from a central position to the posterior.

Diagnosis
The male can be easily recognised by the embolic basal apophysis white and transparent, without obvious sclerotisation (Fig. 6b) and the terminal of embolus not modified (Fig. 7c).Females can be distinguished by the large, oblong epigynal plate, with a pair of hoods posteriorly (Fig. 9A).

Notes
The female is described here for the first time.
with modifications.The type material is deposited at the Institute of Zoology, Chinese Academy of Sciences in Beijing (IZCAS).Abbreviations: ALE anterior lateral eye; AME anterior median eye; C conductor; CD copulatory duct; CO copulatory opening; E embolus; EBA embolic basal apophysis; EBF embolic basal flat extension; EBP embolic basal process; ETA embolic terminal apophysis; FD fertilisation duct; H hood; MA median apophysis; Se septum; PLE posterior lateral eye; PME posterior median eye; S spermatheca; SD sperm duct; ST subtegulum; T tegulum; TTA theridiid tegular apophysis.