Stygothrombium garzensis Li & Guo, 2021

Stygothrombium garzensis Li & Guo , sp. nov. ( Figs 1–5 View Figure 1 View Figure 2 View Figure 3 View Figure 4 View Figure 5 )

Habitat. Interstitial waters.

Material examined. Holotype female, Chaqingsongduo National Nature Reserve, Sichuan, China (31°00′88′′N, 99°24′71′′E, elev. 3523 m), water depth 30–40 cm, located at the hillside, running water with organic detritus, dead wood and leaves on the bottom, collected by Boyan Li, 30.VIII.2020, Slides No. SC-ST-2020080101.

Etymology. “ garze -” is derived from the name of the Garze Tibetan Autonomous Prefecture, Sichuan Province, China, where the specimen was collected.

Diagnosis. Soft and papillate idiosoma vermiform; eyes completely absent; infracapitulum base approximately 3.5 times as long as rostrum; P-A with two stout subventrodistal harpagones, above harpago seta thicker than other one; on one side of P-B, tibia with one four-pronged odontus claws bulging above tarsus; se about half length of posterior portion of prodorsal plate; one seta and two rather long setae at lateral margin of Cx-I; stalked Ac-1–3 arranging in an almost straight line, glv- 2 between Ac-3 and inner posterior angle of Cx-IV, located at one-third of interval near Ac-3 approximately; empodium considerably smaller than lateral claws.

Description. Female (SC-ST-2020080101). Soft and papillate idiosoma vermiform ( Fig. 1A View Figure 1 ); eyes completely absent ( Fig. 2A View Figure 2 ); with eight pairs of gld and seven pairs of gll ( gld- 1–8, gll- 1–7 in Fig. 2A View Figure 2 ), six pairs of glv ( glv- 1–6 in Fig. 2B View Figure 2 ); idiosomal glandularia (or modified stomatoid lyrifissures) without sclerite platelets but surrounded by unpapillate cuticle, a long seta and short seta associated with glandularia except gll -1 with only a short seta ( Figs 1B–C View Figure 1 ); excretory pore placed near posterior end of ventral surface and between glv -5 ( Fig. 2B View Figure 2 ).

Gnathosoma retractable into idiosoma; infracapitulum base approximately 3.5 times as long as rostrum; two pairs of setae on rostrum, posterior one longer than anterior one ( Fig. 3A View Figure 3 ); chelicera two-segmented, basal segment expanded and long ( Fig. 3B View Figure 3 ); fused pedipalp two-segmented: first segment including trochanter + femur + genu (P-A); P-A with numerous dorsal setae, a thin ventrodistal seta, two stout subventrodistal harpagones (above harpago seta thicker than other one) and two ventroproximal setae (one normal seta and one long curved seta); tibia + tarsus fused into short second segment (P-B); on one side of P-B, tibia with one four-pronged odontus claws bulging above tarsus, one stout gladius seta, one thick and short lancea seta, one parodontus, and two normal setae on tarsus; P-B with six normal setae on another side, single solenidion on dorsum and alantoid seta with rounded tip at terminus ( Figs 3C–D View Figure 3 ).

Prodorsal plate bearing vi, si, ve and se; long and narrow posterior portion of prodorsal plate approximately six times as long as short and wide anterior portion; se about half length of posterior portion, longer than vi, si and ve ( Fig. 3E View Figure 3 ).

Coxal plates in four groups; two ACG not fused but close, two PCG widely separated; Cx-I trapezoidal, with numerous setae near inner apical angles and three setae (one seta and two rather long setae) at lateral margin; Cx-II trapezoidal, with one seta near outer posterior angles ( Fig. 4A View Figure 4 ); Cx-III and Cx-IV nearly triangular, with some setae respectively ( Fig. 4B View Figure 4 ).

Genital field with about twenty tiny setae; stalked Ac-1–3 arranging in an almost straight line, interval from Ac-1 to Ac-2 and Ac-2 to Ac-3 almost equal; gonopore surrounded by three or four setae on each side; glv- 2 between Ac-3 and inner posterior angle of Cx-IV, located at one-third of interval near Ac-3 approximately ( Fig. 4B View Figure 4 ).

Legs without swimming setae but numerous setae present; I-L thicker than other pairs of legs, I-L-3–5 with stomatoid lyrifissures on one side ( Figs 5A–D View Figure 5 ); tarsus of I–IV-L with two pectinate lateral claws and one smooth middle empodium, empodium considerably smaller than lateral claws ( Fig. 1D View Figure 1 ).

Male. Unknown.

Measurements ( holotype). Idiosoma L 3857 (from peak of protrusible integument to bottom), W 1114; excretory pore L 108; Infracapitulum L 783, base L 607, rostrum 176; Chelicera base segment L 477, claw L 102; P-A dL 253, P-B dL 97, alantoid seta L 60, above harpago seta L 64, nether harpago seta L 66; prodorsal plate L 478, anterior portion L 73, posterior portion L 405; ACG L 274; PCG L 346; gonopore L 119, Ac-1 L 76, Ac-2 L 66, Ac-3 L 80; Legs segments dL: Ⅰ-L-1 100, Ⅰ- L-2 164, Ⅰ-L-3 173, Ⅰ-L-4 182, Ⅰ-L-5 189, Ⅰ-L-6 159, claw dL 88; II-L-1 88, II-L-2 134, II-L-3 136, II-L-4 166, II-L-5 190, II-L-6 140, claw dL 84; III-L-1 123, III-L-2 134, III-L-3 139, III-L-4 186, III-L-5 205, III-L-6 153, claw dL 78; IV-L-1 101, IV-L-2 173, IV-L-3 213, IV-L-4 259, IV-L-5 280, IV-L-6 191, claw dL 81.

Remarks. The present new species is similar to S. monotrichum Nagasawa & Abé, 2014 from Japan in quantity and location of idiosomal glandularia and pedipalp structures. The new species differs from the latter in the following aspects: (1) idiosoma L 3857 in S. garzensis Li & Guo , sp. nov., but 1560–1830 in S. monotrichum ; (2) glv -1 between ACG and PCG in S. garzensis Li & Guo , sp. nov., while absent in S. monotrichum ; (3) glv- 2 between Ac-3 and inner posterior angle of CxIV in S. garzensis Li & Guo , sp. nov., but located posteromedially to the posterior acetabula in S. monotrichum ; (4) setae on ACG and pedipalp much more multiple than S. monotrichum ; (5) P-A dL 253 in S. garzensis Li & Guo , sp. nov., while P-A dL 88 in S. monotrichum . (Nagasawa & Abé 2014)

Funding This research was supported by National Natural Science Foundation of China (31772421, 31750002), Guizhou Science and Technology Project (Qiankehe Pingtai Rencai [2017] 5788) and National Key R & D Program of China (2017YFD0201000).

Acknowledgements We are grateful to Boyan Li ( Institute of Entomology, Guizhou University, P. R. China) for collecting the specimen and processing the photos. Furthermore, we are thankful to Zhuhui Ding ( Institute of Entomology, Guizhou University, P. R. China) for helping to take photos of specimen .