The genus Pimoa Chamberlin & Ivie, 1943, is highly diverse and currently contains 85 species, of which 67 are distributed in Asia. In this study, a new species of Pimoa is described from Southwest China: P. shimian Wang, Yao & Zhang, sp. nov. (♂♀). This new species is closely related to P. bomi Zhang & Li, 2021, and P. reniformis Xu & Li, 2007. The taxonomic keys for distinguishing these three closely related species and a distribution map of all Asian pimoids are also provided.

Asia, biodiversity, invertebrate, morphology, taxonomy

The Pimoidae Wunderlich, 1986, is currently known to be a sister lineage of the Linyphiidae Blackwall, 1859. Pimoidae once included four genera: Nanoa Hormiga, Buckle & Scharff, 2005; Pimoa Chamberlin & Ivie, 1943; Putaoa Hormiga & Tu, 2008; and Weintrauboa Hormiga, 2003 (Xu et al. 2021). However, based on molecular and morphological data, Hormiga et al. (2021) revised the classification of this family, transferring Putaoa and Weintrauboa to Linyphiidae. Therefore, Pimoidae currently contains 86 extant species, belonging to two genera: Pimoa and Nanoa (WSC 2024). Despite significant morphological differences between Nanoa and Pimoa, previous research has supported the idea that these two genera are sister groups (Hormiga et al. 2005, 2021). Species of the monotypic genus Nanoa are distributed only in the West of the Rockies, USA. Pimoa is the most species-rich genus in Pimoidae, with 85 species distributed disjunctly across three mountainous regions of the Northern Hemisphere: the western Nearctic (from Washington to California), the western Mediterranean, and Asia (from the Himalaya to Beijing) (Lin et al. 2023). For the global transoceanic disjunctions of pimoids, Wang et al. (2008) proposed that vicariance, driven by the breakup of Laurasia, played a major role in shaping the distribution pattern. Hormiga et al. (2021) proposed that pimoids were originally distributed in the ancestral boreotropical forests of the northern latitudes. Post-Eocene gradual cooling and aridification led to the retreat of those ancestral forests, resulting in the fragmentation of pimoid distributions.

Pimoids were once considered a relict lineage and had long been considered to exhibit low species diversity (Hormiga 1994). By 2019, only four pimoid species were known to occur in the Alps and Pyrenees (Mammola et al. 2016), 15 in the West of the Rockies (Hormiga and Lew 2014), and 12 in Asia (Zhang and Li 2019). However, in recent years, an unexpectedly high diversity of Pimoa (54 species) has been revealed in the Pan-Himalayan region (Himalayas, Tibet, and Hengduan Mountains), leading to its recognition as the diversity center for Pimoidae, accounting for 76% of the total diversity (Xu et al. 2021; Irfan et al. 2022). Among Asian pimoids, China exhibits remarkable diversity, with 49 species recorded to date. Therefore, we recently conducted a field survey targeting pimoids in Southwest China and discovered a new species of Pimoa (Fig. 1). In this paper, we have photographed and described this new species. Additionally, we provide taxonomic keys to distinguish it from two other morphologically similar species that also occur in Southwest China.

Figure 1. 

Distribution records of all Asian pimoids. The green triangle represents Pimoa shimian sp. nov., the blue rectangle represents a new record of P. reniformis, and red dots represent the type localities of 67 known species. 1 P. anatolica Hormiga, 1994 2 P. anning Zhang & Li, 2021 3 P. binchuanensis Zhang & Li, 2019 4 P. bomi Zhang & Li, 2021 5 P. cawarong Zhang & Li, 2021 6 P. clavata Xu & Li, 2007 7 P. cona Zhang & Li, 2020 8 P. crispa Fage, 1946 9 P. daman Zhang & Li, 2021 10 P. danba Zhang & Li, 2021 11 P. deqen Zhang & Li, 2021 12 P. dongjiu Zhang & Li, 2021 13 P. duiba Zhang & Li, 2020 14 P. exigua Irfan, Wang & Zhang, 2021 15 P. gagna Zhang & Li, 2021 16 P. gandhii Hormiga, 1994 17 P. guiqing Zhang & Li, 2021 18 P. gyaca Zhang & Li, 2021 19 P. gyara Zhang & Li, 2021 20 P. gyirong Zhang & Li, 2021 21 P. heishui Zhang & Li, 2021 22 P. indiscreta Hormiga, 1994 23 P. jinchuan Zhang & Li, 2021 24 P. khaptad Zhang & Li, 2021 25 P. koshi Zhang & Li, 2021 26 P. lata Xu & Li, 2009 27 P. lemenba Zhang & Li, 2020 28 P. lhatog Zhang & Li, 2021 29 P. lihengae Griswold, Long & Hormiga, 1999 30 P. mainling Zhang & Li, 2020 31 P. mechi Zhang & Li, 2021 32 P. miandam Zhang & Li, 2021 33 P. miero Zhang & Li, 2021 34 P. mude Zhang & Li, 2021 35 P. muli Zhang & Li, 2021 36 P. nainital Zhang & Li, 2021 37 P. naran Zhang & Li, 2021 38 P. nematoides Hormiga, 1994 39 P. ninglang Zhang & Li, 2021 40 P. nyalam Zhang & Li, 2021 41 P. nyingchi Zhang & Li, 2020 42 P. phaplu Zhang & Li, 2021 43 P. pingwuensis Irfan, Wang, Zhao & Zhang, 2022 44 P. putou Zhang & Li, 2021 45 P. rara Zhang & Li, 2021 46 P. reniformis Xu & Li, 2007 47 P. rongxar Zhang & Li, 2020 48 P. samyai Zhang & Li, 2020 49 P. sangri Zhang & Li, 2021 50 P. shigatse Zhang & Li, 2021 51 P. shimian sp. nov. 52 P. shoja Zhang & Li, 2021 53 P. sinuosa Hormiga, 1994 54 P. tengchong Zhang & Li, 2021 55 P. thaleri Trotta, 2009 56 P. trifurcata Xu & Li, 2007 57 P. wanglangensis Yuan, Zhao & Zhang, 2019 58 P. wulipoensis Irfan, Wang & Zhang, 2021 59 P. xiahe Zhang & Li, 2021 60 P. xinjianensis Zhang & Li, 2019 61 P. yadong Zhang & Li, 2020 62 P. yajiangensis Irfan, Wang, Zhao & Zhang, 2022 63 P. yejiei Zhang & Li, 2021 64 P. yele Zhang & Li, 2021 65 P. zayu Zhang & Li, 2021 66 P. zekogensis Irfan, Wang, Zhao & Zhang, 2022 67 P. zeluni Lin & Li, 2023 68 P. zhigangi Zhang & Li, 2021.

Specimens were examined with a LEICA M205C stereomicroscope. Images were captured with a Canon EOS 750D wide-zoom digital camera (24.2 megapixels) mounted on the stereomicroscope mentioned above and assembled using Helicon Focus v. 3.10.3 image stacking software (Khmelik et al. 2005). Epigyne and male palp were examined after dissection. The left palp was illustrated. Epigyne was removed and treated in a warmed 10% potassium hydroxide (KOH) solution.

All measurements were obtained using a LEICA M205C stereomicroscope and are given in millimeters. We measured the length of the legs and body using an ocular micrometer. Eye sizes were measured as the maximum diameter from either dorsal or frontal views. Leg measurements are shown as total length (femur, patella + tibia, metatarsus, tarsus). The terminology used in the text and the figure legends follows Hormiga (1994). The distribution map was generated with ArcGIS v. 10.2 (ESRI Inc.). Abbreviations used in this paper and in the figure legends: ALE = anterior lateral eye, AME = anterior median eye, AME–ALE = distance between AME and ALE, AME–AME = distance between AMEs, AS = alveolar sclerite, C = conductor, CD = copulatory duct, CDP = cymbial denticulate process, CO = copulatory opening, DP = dorsal plate of the epigyne, E = embolus, FD = fertilization duct, MA = median apophysis, P = paracymbium, PCS = pimoid cymbial sclerite, PEP = pimoid embolic process, PLE = posterior lateral eye, PME = posterior median eye, PME–PLE = distance between PME and PLE, PME–PME = distance between PMEs, S = spermatheca, T = tegulum, VP = ventral plate of epigyne. All specimens are deposited in the College of Life Science, Shenyang Normal University (SYNU) in Liaoning, China.

Family Pimoidae Wunderlich, 1986

Genus Pimoa Chamberlin & Ivie, 1943

Pimoa: Chamberlin and Ivie 1943: 9; Hormiga 1994: 4; Hormiga and Lew 2014: 1; Mammola et al. 2016: 1.

Note

In 1943, Chamberlin and Ivie erected the genus Pimoa, which included four pimoid North American species that had previously been placed within the genus Labulla Simon, 1915, plus three new North American species. Then, Hormiga (1993) synonymized Louisfagea Brignoli, 1971, with Pimoa, raised Pimoinae Wunderlich, 1986, to family rank, and brought an end to the history of pimoids being placed in different families.

Diagnosis

Pimoa (total length ranges from 4.00–12.0 mm) is larger in size than Nanoa (1.42–1.65 mm). The males of Pimoa can be distinguished from Nanoa by the long and membranous pimoid embolic process and the elongate cymbial denticulate process with many cuspules (vs. the pimoid embolic process absent and short cymbial process only with one strong cuspule) (Fig. 2; Hormiga et al. 2005: figs 1, 2). The females of Pimoa can be distinguished from Nanoa by the absence of a ventral scape-like septum (vs. epigynum with a distinct septum) (Fig. 3A; Hormiga et al. 2005: figs 3, 5).

Figure 2. 

Left palp of Pimoa shimian sp. nov., holotype A. Prolateral view; B. Ventral view; C. Retrolateral view. Abbreviations: AS = alveolar sclerite; C = conductor; CDP = cymbial denticulate process; E = embolus; MA = median apophysis; P = paracymbium; PCS = pimoid cymbial sclerite; PEP = pimoid embolic process; T = tegulum. The blue arrow represents the tegular apophysis. Scale bar: 0.50 mm (A–C).

Figure 3. 

Epigyne and habitus of Pimoa shimian sp. nov., female paratype and male holotype A. Epigyne, ventral view; B. Vulva, dorsal view; C. Schematic course of internal copulatory duct system, ventral view; D. Schematic course of internal copulatory duct system, dorsal view; E. Male habitus, dorsal view; F. Female habitus, dorsal view; G. Female habitus, ventral view. Abbreviations: CD = copulatory duct; CO = copulatory opening; DP = dorsal plate of the epigyne; FD = fertilization duct; S = spermatheca; VP = ventral plate of epigyne. Scale bars: 0.10 mm (A–D); 1.00 mm (E–G).

Composition

The 85 Pimoa species are known from the northern hemisphere, with 14 from the western Nearctic, four from the western Mediterranean (Italy, France, and Spain), two from Pakistan, seven from India, nine from Nepal, and 49 from China (WSC 2024).

Type species

Labulla hespera Gertsch & Ivie, 1936, from California, USA.

Identification keys to three closely related species from Southwest China

Males

1	Tegulum with pointed apophysis; pimoid cymbial sclerite nearly U-shaped (Fig. 2)	P. shimian sp. nov.
–	Tegulum without apophysis; pimoid cymbial sclerite nearly V-shaped (Fig. 4)	2
2	Cymbial denticulate process short and broad; paracymbium short, ca. 1/5 of cymbial length, finger-shaped (Fig. 4A, C, E)	P. bomi
–	Cymbial denticulate process narrow and distally curved; paracymbium short, ca. 1/4 of cymbial length, hook-shaped (Fig. 4B, D, F)	P. reniformis

Females

1	Spermathecae separated by ca. 1/3 the width of a spermatheca; dorsal plate narrow and distally blunt (Fig. 3A, B)	P. shimian sp. nov.
–	Spermathecae unseparated; dorsal plate broad and distally pointed (Fig. 5)	2
2	Spermathecae round; copulatory ducts linear and with 3 strong turns (Fig. 5A, B, E, F)	P. bomi
–	Spermathecae nearly bean-shaped; copulatory ducts broad, with 2 strong turns and with posterior part narrower than 1/4 width of anterior part (Fig. 5C, D, G, H)	P. reniformis

 Pimoa bomi Zhang & Li, 2021

Figs 1, 4A, C, E, 5A, B, E, F

Pimoa bomi Zhang & Li, in Xu et al. 2021: 9, figs 3, 4, 54B (♂♀).

Type material examined

Holotype : • ♂ (IZCAS-Ar41925), China, Tibet, Nyingchi, Bomi Co., Karlung Vill. (30.04°N, 95.56°E, 3147 m), 26 Jul. 2019, X. Zhang et al. leg. Paratypes: • 1♂2♀ (IZCAS-Ar41926-Ar41928), same data as holotype.

Figure 4. 

Pimoa bomi (A, C, E), P. reniformis (B, D, F) A, B. Prolateral view; C, D. Ventral view; E, F. Retrolateral view. Abbreviations: AS = alveolar sclerite; C = conductor; CDP = cymbial denticulate process; E = embolus; MA = median apophysis; P = paracymbium; PCS = pimoid cymbial sclerite; PEP = pimoid embolic process; T = tegulum. A, C, E were modified from Xu et al. (2021). Scale bars: 0.30 mm (A–F).

Note

Cheliceral stridulatory striae present in the male, vestigial in the female.

Figure 5. 

Pimoa bomi (A, B, E, F), P. reniformis (C, D, G, H) A, C. Epigyne, ventral view; B, D. Schematic course of internal copulatory duct system, ventral view; E, G. Vulva, dorsal view; F, H. Schematic course of internal copulatory duct system, dorsal view. Abbreviations: CD = copulatory duct; CO = copulatory opening; DP = dorsal plate of the epigyne; FD = fertilization duct; S = spermatheca; VP = ventral plate of epigyne. A, B, E, F were modified from Xu et al. (2021). Scale bars: 0.30 mm (A–H).

With more new pimoid species being discovered in the Pan-Himalaya, it has become a diversity center of pimoids (WSC 2024). However, the map of Asian pimoids reveals that there are still large areas where pimoids have not been recorded (Fig. 1), such as eastern Tibet, western Sichuan, and southern Qinghai. Therefore, we believe that more new pimoids will be reported with further collections. We have recently collected abundant pimoid specimens in the Pan-Himalaya, and further molecular systematic research in pimoids will shed more light on true species diversity and diversification processes in this region.

The manuscript has greatly benefited from the comments provided by Danilo Harms, Gustavo Hormiga, and an anonymous reviewer. We thank Yuri M. Marusik (Magadan, Russia) for language editing and Ying Wang for his contribution to the collection of specimens. This study is supported by the Basic Scientific Research Support Project of Liaoning Province (LJ232410166067).