Nesticella occulta, Ballarin & Eguchi, 2023

Ballarin, Francesco & Eguchi, Katsuyuki, 2023, Integrative taxonomic revision of the genera Nesticella and Howaia in Japan with the description of five new species (Araneae, Nesticidae, Nesticellini), ZooKeys 1174, pp. 219-272 : 219

Nesticella occulta sp. nov.

Figs 11A-E ; 13F , 15D , 16B (Japanese name: kakure-horahimegumo カクレホラヒメグモ)

Material examined.

♀ Holotype: Japan: Okinawa Pref.: Ishigaki-jima Is.: Kabira, Kabirano-ana cave (川平の穴), long and superficial cave with many rocks, in the dark zone of the cave, 24.47384°N, 124.13416°E, 20.Sep.2022, F. Ballarin leg. (NSMT-Ar 25259) . Paratypes: 1♀, same locality as the holotype, 1.Apr.2019, K. Uchida leg. (NSMT-Ar 25260) ; 1♀, same locality, 2.Jan.2022, K. Uchida leg. (RMUF) ; 2♀, same locality and date as the holotype, F. Ballarin leg. (FBPC) .

Other material examined.

1♂ subad., same locality as the holotype, 16.Oct.2020 ; 1♂ subad., same locality, 2.Jan.2022 ; 1♂ subad., same locality, 28.Mar.2022 , all K. Uchida leg. (RMUF).

Etymology.

The specific name derives from the Latin adjective occultus (= hidden, secret). It refers to the troglobitic lifestyle and rarity of the species, hidden in the deep recess of a single cave in Ishigaki-jima Is.

Diagnosis.

This species closely related to N. kaohsiungensis Lin, Ballarin & Li, 2016 from Taiwan. The new species can be easily distinguished from N. kaohsiungensis by the strongly reduced eyes and the lack of pigmentation and pattern on the opisthosoma (vs eyes well-developed, clear pattern on the opisthosoma and pigmentation present in N. kaohsiungensis ) (Fig. 11A, B cf. Lin et al. 2016: fig. 69A, C). In addition, the female of this species can be distinguished from the female of N. kaohsiungensis by the different shape of scapus, lacking a lobated tip (vs ending with a lobated tip in the latter species) (Figs 11C, D , 13F cf. Lin et al. 2016: fig. 69E, F).

Description.

Female (holotype). Habitus as in Fig. 11A , 15D . Total length 2.48. Prosoma 1.08 long, 0.93 wide. Carapace piriform, uniformly pale yellowish. Cephalic area as in Fig. 11B . Eyes completely degenerated. Cervical groove and fovea indistinct. Chelicerae uniformly brownish. Labium, maxillae, and sternum pale yellowish as carapace. Legs uniformly pale yellowish. Legs measurements: I 6.36 (2.18, 0.47, 1.48, 1.46, 0.77), II 6.13 (1.97, 0.45, 1.60, 1.42, 0.69), III 4.36 (1.43, 0.38, 0.95, 0.90, 0.70), IV 6.02 (1.94, 0.46, 1.54, 1.32, 0.76). Opisthosoma uniformly greyish, covered by long, sparse hairs.

Epigyne and vulva as in Figs 11C-E , 13F . Scapus (Sc) long and protruding, tongue-like, ~ 2 × longer than wide, ending with a rounded tip (Figs 11C, D , 13F ). Copulatory opening (Co) at the inner-lateral sides of scapus. Internal ducts slightly visible through the transparent tegument, V shaped. Copulatory ducts (Cd) short and straight, strongly diverging from each other (Figs 11C-E , 13F ) distal trait coiled, reaching spermathecae with 1 coil. Insemination ducts (Id) thin, coiled around the copulatory ducts. Spermathecae (S) small and rounded, separated from each other by ~ 2.5 × their diameter (Fig. 11E ).

Male. Unknown.

Size variation.

(based on 4 females) Total length: 1.75-2.48, prosoma length: 1.06-1.10, width: 0.92-0.94 wide.

Distribution.

Ishigaki-jima Island. Known only from the type locality (Fig. 16B ).

Habitat and ecology.

Nesticella occulta sp. nov. lives in the dark zone of the type locality cave characterized by high and stable temperature and humidity (e.g., temp: 25.8 °C, hum: 94.4%) (Fig. 15H ). It builds small and simple scaffold-webs among the crevices and empty spaces between the numerous rocks covering the floor of the cave and on the lower part of the cave walls. These spiders appear scattered inside the cave and rather infrequently, suggesting a relatively small population. The compete eyes degeneration, the lack of pigmentation and the presence of the species only in the deepest section of the cave suggest that N. occulta sp. nov. is a true troglobiont. These characteristics as well as the rarity of the species, inhabiting a single cave, make N. occulta sp. nov. a good target for species conservation.

Nesticella okinawaensis group

Figures

Figure 11. Nesticella occulta sp. nov. A habitus of female (holotype) B cephalic area of female, frontal view C female epigyne, ventral view D same, shape variation E vulva, dorsal view. Abbreviations: Cd - copulatory duct; Co - copulatory opening; Id - insemination duct; S - spermatheca; Sc - scapus. Scale bars: 1.0 mm (A, C); 0.2 mm (B, D, E).

Figure 13. Genitalia of Nesticella okinawaensis, Howaia subterranea sp. nov., and N. occulta sp. nov. A male palp of N. okinawaensis, ventral view B same, retrolateral view C detail or paracymbium, dorsal view D female epigyne, ventral view; E H. subterranea sp. nov., female epigyne, ventral view F N. occulta sp. nov. female epigyne, ventral view. Abbreviations: Ca - apophysis of the retrolateral process of conductor; Cl - lobe of conductor; Cm - median process of conductor; Co - copulatory opening; Cp - prolateral process of conductor; Cr - retrolateral process of conductor; Di I-II - distal processes I and II of paracymbium; E - embolus; P - paracymbium; Ra - radical apophysis; Rx - radix; S - spermatheca; Sc - scapus; Sd - sperm duct; St - subtegulum; Te - tegulum; Ve - ventral process of paracymbium. Scale bars: 0.2 mm.

Figure 15. Nesticella and Howaia species in life and their natural habitats A female of H. mogera B female of N. terrestris C female of H. alba sp. nov. D female of N. occulta sp. nov. E female of N. okinawaensis F example of the epigean habitat of Nesticella species in the Ryukyus G habitat of H. alba sp nov. (dark zone of Tsuzupisuki-abu cave) H habitat of N. occulta sp. nov. (dark zone of Kabirano-ana cave) (all photos by F. Ballarin).

Figure 16. Distribution of Nesticella and Howaia species in mainland Japan and Ryukyu Archipelago A distribution of N. brevipes and N. terrestris in mainland Japan and neighboring countries B distribution of Nesticella and Howaia species endemic to the Ryukyu Archipelago C distribution of H. mogera in mainland Japan and neighboring countries D distribution of H. mogera in the Ryukyu Archipelago and neighboring countries. Colored squares refer to the type localities of the species, colored dots indicate the locations of specimens whose morphology has been checked during this study, dashed areas refer to the generally known distribution of the species, question marks refer to unclear distributions (see " remarks on misidentifications " of N. brevipes and N. terrestris).