Stygothrombium garzensis Li & Guo, 2021

Li, Haitao, Jin, Daochao & Guo, Jianjun, 2021, A new species of the genus Stygothrombium, representing a newly recorded superfamily Stygothrombioidea Mullen & Vercammen-Grandjean, 1980 (Acari: Stygothrombiae) from China, Zoological Systematics 46 (4), pp. 281-288 : 283-287

Stygothrombium garzensis Li & Guo , sp. nov. ( Figs 1–5 )

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 ); eyes completely absent ( Fig. 2A ); with eight pairs of gld and seven pairs of gll (gld- 1–8, gll- 1–7 in Fig. 2A ), six pairs of glv (glv- 1–6 in Fig. 2B ); 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 ); excretory pore placed near posterior end of ventral surface and between glv -5 ( Fig. 2B ).

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 ); chelicera two-segmented, basal segment expanded and long ( Fig. 3B ); 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 ).

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 ).

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 ); Cx-III and Cx-IV nearly triangular, with some setae respectively ( Fig. 4B ).

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 ).

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 ); tarsus of I–IV-L with two pectinate lateral claws and one smooth middle empodium, empodium considerably smaller than lateral claws ( Fig. 1D ).

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 .

Figures

Figure 1. Stygothrombium garzensis Li & Guo, sp. nov., ♀, holotype (SC-ST-20200801). A. Ventral view. B. Gll-1. C. Gll-2. D. I-L-4, stomatoid lyrifissures. Scale bars: A=500μm; B–D=10μm.

Figure 2. Stygothrombium garzensis Li & Guo, sp. nov., ♀, holotype (SC-ST-20200801).A. Dorsal view. B. Ventral view. Scale bars =500μm.

Figure 3. Stygothrombium garzensis Li & Guo, sp. nov., ♀, holotype (SC-ST-20200801).A. Infracapitulum, dorsal view. B. Chelicera. C. Pedipalp, one lateral view. D. Pedipalp, another lateral view. E. Prodorsal plate. Scale bar=200μm.

Figure 4. Stygothrombium garzensis Li & Guo, sp. nov., ♀, holotype (SC-ST-20200801). A. Anterior coxal group (Cx-I+Cx-II). B. Posterior coxal group (Cx-III+Cx-IV), genital field. Scale bar=200μm.

Figure 5. Stygothrombium garzensis Li & Guo, sp. nov., ♀, holotype (SC-ST-20200801). A. I-L-1–6. B. II-L-1–6. C. III-L-1–6. D. IV-L-1–6. Scale bar=200μm.