Female (Holotype, IZCAS-Ar43547): Habitus as in Fig. 2A and B. Carapace 10.88 long, 8.62 wide, 8.92 high. Carapace nearly equally wide at pars cephalica and pars thoracica. Carapace red-brown with white setae; pars cephalica elevated. Eye sizes and interdistances: AME 0.21, ALE 0.26, PME 0.51, PLE 0.33, AME–AME 0.37, AME–ALE 3.56, PME–PME 0.65, PME–PLE 2.52, AME–PME 0.11. Pars cephalica with a pointed posterior margin dorsally, almost as long as wide. Chelicerae covered with narrowed white and black setae. Legs with a white ring of setae at joints. Legs with ventral macrosetae on Ta, Mt and Ti I–IV. Leg measurements: I: 17.83 (5.17+5.90+3.94+2.82); II: 16.46 (5.54+5.89+2.94+2.09); III: 14.77 (4.80+5.68+2.63+1.66); IV: 19.53 (6.33+7.29+3.74+2.17). Abdomen dark brown, covered with black setae, with white spots, sigilla conspicuous, surrounded by white setae.

Figure 1.  

Eresus da sp. n. holotype female. A habitat; B microhabitat; C tunnel wrapped with beetle skeleton; D beetle skeleton (Pimeliinae sp.); E spider with nest.

Figure 2.  

Eresus da sp. n. holotype female (A, B) and E. yukuni sp. n. holotype male (C, D), habitus. A, C dorsal view; B, D lateral view.

Epigyne (Fig. 3) with sclerotised margins, longer than high. Middle plant beyond posterior edge of epigyne margin. Fissure bow-shaped. Copulatory duct translucent, with spermathecal epithelium on anterior edge. Spermathecae distinctly lobed, reaching further laterally than copulatory ducts.

Figure 3.  

Eresus da sp. n. holotype female A epigyne, ventral view; B vulva, dorsal view.

Male. Unknown.

Females of Eresus da sp. n. are similar to those of E. kollari by a relatively gentle slope of the ocular area (Fig. 2C and D; Řezáč et al. 2008, fig. 4D; Miller et al. 2012, fig. 2F) and with the epigynal area longer than high (Fig. 3A; Řezáč et al. 2008, figs. 2A–J). This species can be distinguished from E. kollari by the abdomen with a large number of white spots (Fig. 2D) (vs. abdomen uniformly black in E. kollari), the anterior edge of copulatory duct within the anterior edge of epigyne (vs. beyond the anterior edge of epigyne in E. kollari) and the ventral of fissure curved (vs. almost straight in E. kollari) (Fig. 4).

Figure 4.  

Eresus spp., outlines of copulatory organs (green line, Eresus da sp. n.; red line, E. kollari, changed after Řezáč et al. (2008). A epigyne, ventral view; B vulva, dorsal view.

The species name is a noun in apposition derived from the Chinese pinyin “dà” (giant) and refers to the large size of this new species.

Known only from the type locality (Xinjiang, China).

The spider was found behind a clump of desert plants (Fig. 1A). The spider habitat is under the ground, with a silk tunnel (around 20 cm in length) connecting its opening and underground nest (Fig. 1A and B). This underground living strategy may be an adaptive strategy for escaping from the sunlight heating and extremely high temperature of the ground surface. As the silken tunnel was wrapped with dozens of empty beetle exoskeletons (Fig. 1C and D), we assume that the desert-living beetles are the main diet of the spider, which has a thick fang to pierce the beetles while feeding. In addition, the small size of the spider’s eyes suggest that the spider may adopt a sit-and-wait hunting strategy and that it does not rely on visual signals for hunting.

Male (Holotype, IZCAS-Ar43546): Habitus as in Figs. 2C and D. Total length: 6.48, carapace 3.35 long, 2.44 wide, 1.76 high. Abdomen 3.20 long, 2.88 wide. Carapace black with white setae; pars cephalica elevated. Eye sizes and interdistances: AME 0.09, ALE 0.13, PME 0.18, PLE 0.08, AME–AME 0.12, AME–ALE 0.78, PME–PME 0.19, PME–PLE 1.03, AME–PME 0.04, ALE–PLE 1.88. Pars cephalica with a pointed posterior margin dorsally, almost as long as wide (2.54 long, 2.83 wide). Chelicerae covered with black and few white setae. Leg I with a white ring of setae at joints, black; leg II–IV with white setae dorsally. Leg measurements: Leg I 6.54 (1.95+2.15+1.32+1.12); leg II 5.11 (1.51+1.67+1.00+0.93); leg III 4.55 (1.47+1.50+0.81+0.77); leg IV 6.12 (1.93+2.22+1.14+0.83). Abdomen dark brown, with four black spots, covered with dense white setae dorsally; ventrum with black setae, sigilla conspicuous, surrounded by black setae.

Palp (Fig. 5). Tegulum round. Conductor height is greater than width, with a slight shoulder and curved terminal tooth; the height of the lamella is almost twice the length of terminal tooth; groove deep and narrow.

Figure 5.  

Eresus yukuni sp. n., holotype, right palp (Horizontal flip). A conductor, prolateral view; B same, ventral view; C same, retrolateral view; D palp, prolateral view; E same, retrolateral view.

Female. Unknown.

Male of Eresus yukuni sp. n. is similar to the E. lavrosiae Mcheidze, 1997 by having black carapace covered with short black and white setae that is almost as wide at the pars cephalica as it is at the pars thoracica (Fig. 2A and B; Zamani et al. 2020, fig. 15). However, this species can be distinguished from E. lavrosiae by the abdomen with dense white setae dorsally (Fig. 2A) [vs. with a frontally abrupt white circle in E. lavrosiae (Zamani et al. 2020, fig. 15)]. The palps are similar to those of E. lavrosiae by the strongly curved terminal tooth and the conspicuously deep lamellar groove, but can be distinguished by the shoulder near the base of the embolus in retrolateral view (Fig. 5B) (vs. shoulder far from the base of the embolus in E. lavrosiae (Zamani et al. 2020, fig. 19) and the conductor higher than wide in ventral view (Fig. 5C) [vs. wider than high in E. lavrosiae (Zamani et al. 2020, fig. 18)].

The species is named after Mr. Kun Yu, who collected the holotype; noun (name) in the genitive case.

Known only from the type locality (Xinjiang, China).