Nihonella chika, Ballarin & Yamasaki, 2021

Ballarin, Francesco & Yamasaki, Takeshi, 2021, Nihonella gen. nov., a new troglophilic genus of dwarf spiders from Japan with a discussion on its phylogenetic position within the subfamily Erigoninae (Araneae, Linyphiidae), European Journal of Taxonomy 733, pp. 1-18 : 8-14

Nihonella chika gen. et. sp. nov.

urn:lsid:zoobank.org:act:87924F73-CCDB-4872-99A3-20A5A3A4EBE9

Figs 1 A–G, 2–4 ; Table 1

Diagnosis

Male Nihonella chika gen. et. sp. nov. can easily be distinguished from males of species of the Savignia group by the clearly visible hypertrophic secondary DSA apophysis, long and hooked, which instead is absent or much shorter in species of Savignia and usually straight and tooth-shaped (see Figs 2 A–B, D, 3A–C, 4A–E vs Millidge 1977: figs 122–144). Another distinct character of the male Nihonella chika gen. et. sp. nov. is the shape of the prolateral tibial apophysis of the palp: long, partially covering the middle line of the cymbium, and ending with a triangular structure covered with short, stocky spikes ( Figs 2 A–C, 3A–B, D, 4E–F). Female Nihonella chika gen. et. sp. nov. are easily recognized by the general shape of the epigyne, which has two ovoid, flat inflations of the copulatory ducts where the lateral walls of the epigyne join to each other; further, the anterior wall protrudes slightly ( Figs 2E , 3E ). The epigyne also has a trapezoidal posterior median plate ( Figs 2 F–G, 3F), and a twisted course of the copulatory ducts ( Figs 2H , 3G ).

Etymology

The specific name is derived from the Japanese word ʻ chika ʼ (地下) meaningʻ underground, subterraneanʼ and thus refers to the habitat of the species, but it is also the pronunciation of a feminine given name in the Japanese language. Name in apposition.

Material examined

Holotype JAPAN • ♂; Honshu Island, Okayama Prefecture, Takahashi-shi , Kawakamichō , Kōyamaichi , Anatoyama Shrine, Anatoyama cave (穴 門山洞窟); 34.7440° N, 133.3918° E; 480 m a.s.l.; 22 Apr. 2019; Ballarin F. and Yamasaki T. leg.; narrow and long cave behind a Shinto shrine; NSMT-Ar 20909 .

Paratypes JAPAN • 1 ♂, 14 ♀♀; same collection data as for holotype; NSMT-Ar 20910 • 1 ♂, 10 ♀♀; Niimi-shi , Toyonagauyama, Uyama-do cave ( 宇山洞); 34.94226° N, 133.57499° E; 423 m a.s.l.; 21 Apr. 2019; Ballarin F. and Yamasaki T. leg.; large and deep humid cave with a subterranean creek; NSMT-Ar 20911 .

Other material JAPAN • 1♀; Honshu Island, Nara Prefecture, Yoshino District,Tenkawa-shi , Dorogawa, Komorinoiwaya cave (蝙蝠の窟); 34.2686° N, 135.8906° E; 06 Oct. 2019; Ballarin F. and Tanikawa A. leg.; NSMT-Ar 20912 .

Description

Male (holotype)

HABITUS. As shown in Fig. 1 A–C.

MEASUREMENTS. Total length: 1.79, carapace 0.97 long, 0.75 wide.

PROSOMA. Carapace, chelicerae, labium, and sternum uniformly light brownish. Head distinctly raised, AME = 0.04, PME, ALE, PLA = 0.06. Anterior margin of cheliceral groove bearing 5 robust teeth.

OPISTHOSOMA. Opisthosoma uniformly grayish, lacking any pattern, covered with numerous short hairs. Central area of ventral side of opisthosoma slightly lighter.

LEGS. Legs uniformly light brownish. Femur I with 1 prolateral spine. Patella I and Tibia I with 1 dorsal spine. Tibial spine formula = 1.1.1.1. One trichobothrium on metatarsi I–III, absent on metatarsus IV. TmI = approx. 0.55. Leg measurements as follows: Leg I: 3.02 (0.84, 0.23, 0.80, 0.71, 0.44); Leg II: 2.92 (0.81, 0.24, 0.73, 0.66, 0.48); Leg III: 2.44 (0.68, 0.23, 0.58, 0.56, 0.39); Leg IV: 3.15 (0.87, 0.26, 0.82, 0.69, 0.51).

PALP. As shown in Figs 2 A–D, 3A–D, 4E–F. Embolic division as in Fig. 4 A–D. Palpal tibia bearing 1 trichobotrium and long prolateral tibial apophysis approximately as long as the cymbium and partially covering it along its median line. PTA triangle-shaped when observed dorsally, ending with triangular spiked structure. Cymbium ovoid when observed dorsally, covering whole bulb with exception of the tip of secondary branch of distal suprategular apophysis. Deep groove along middle line of cymbium, in which rests ventral part of PTA. Paracymbium stumpy and simple, lacking in apophyses. Tailpiece of radix slightly protruding, with well-developed, thin apophysis, hook-like and frontally-oriented. DSA well-developed, hook-like and ending with blunt tip. Secondary branch of distal suprategular apophysis hypertrophic, long and thin, strongly protruding frontally and ventrally, ending with sharp tip. Median membrane transparent and barely visible, protruding retrolaterally. Embolus hook-like, initial trait oriented frontally then ventro-posteriorly, stumpy, ending with blunt end near tip of DSA.

Female (based on three paratypes)

HABITUS. As shown in Fig. 1 D–G.

MEASUREMENTS. Total length: 2.10-2.47, carapace 1.00-1.06 long, 0.80-0.83 wide.

PROSOMA AND OPISTHOSOMA. Coloration and other details of carapace, chelicera, and opisthosoma as in male. Head only slightly raised.

LEGS. Legs coloration, tibial spine formula, trichobothria and TmI as in male. Leg measurements as follows (based on one paratype): Leg I: 3.59 (1.02, 0.3, 0.95, 0.77, 0.55); Leg II: 3.36 (0.95, 0.28, 0.87, 0.75, 0.51); Leg III: 2.87 (0.81, 0.25, 0.71, 0.68, 0.42); Leg IV: 3.65 (1.05, 0.3, 1.01, 0.82, 0.47).

EPIGYNE AND VULVA. As shown in Figs 2 E–H, 3E–G. Lateral walls converging anteriorly. Anterior wall of epigyne with small projection. End of copulatory ducts with inflation, forming two small, transparent, ovoid plates in central part of the epigyne. Internal ducts visible through epigyne by transparency. Posterior medium plate larger than wide, approximately trapezoidal when epigyne is observed dorsally. Receptacles subspherical, located lateral to the PP. Copulatory ducts starting from posterior/inner side of receptacles, initial trait oriented towards posterior part of the epigyne, then turning frontally before reaching copulatory opening with twisted course. Copulatory openings located under ovoid plates, approximately at joining point of lateral walls.

Ecology and habitat

Although lacking extreme troglomorphic characters (e.g., eye loss), N. chika gen. et. sp. nov. shows troglophilic adaptations, such as body depigmentation. This species has only been found inside caves, several meters from the entrance, in the twilight and transition zones where the light is strongly reduced or absent. N. chika gen. et. sp. nov. builds small sheet-webs inside cracks or empty spaces between rocks on the cave floor.

Distribution

Endemic to Western Honshu, Japan. Currently known only for few caves in Okayama and Nara Prefectures ( Fig. 6 ). Type locality: Anatoyama cave (穴 門山洞窟) in Okayama Prefecture ( Fig. 1H ).

Figures

Fig. 1. Habitus and habitat of Nihonella chika gen. et. sp. nov. A. ♂, holotype (NSMT-Ar 20909), habitus, dorsal view. B. Ditto, ventral view. C. Ditto, lateral view. D. ♀, paratype (NSMT-Ar 20910), habitus, dorsal view. E. Ditto, ventral view. F. Ditto, lateral view. G. Ditto, cephalic region, frontal view. H. Entrance of Anatoyama Cave, type locality of the species. Scale bar = 1 mm.

Fig. 2. Genitalia of Nihonella chika gen. et. sp. nov. A. ♂, holotype (NSMT-Ar 20909), palp, retrolateral view. B. Ditto, prolateral view. C. Ditto, dorsal view. D. Ditto, ventral view. E. ♀, paratype (NSMT- Ar 20910), epigyne, ventral view. F. Ditto, dorsal view. G. Ditto, posterior view. H. Ditto, vulva after being cleared, ventral view. Scale bars: A–D = 0.2 mm; E–H = 0.1 mm.

Fig. 3. Nihonella chika gen. et. sp. nov. A. ♂, holotype (NSMT-Ar 20909), palp, retrolateral view. B. Ditto, prolateral view.C. Ditto, ventral view.D. Ditto, palpal tibia, dorsal view.E. ♀, paratype (NSMT- Ar 20910), epigyne, ventral view. F. Ditto, dorsal view. G. Ditto, vulva, dorsal view. Abbreviations: see Material and methods. Scale bar = 0.1 mm.

Fig. 4. Embolic division and details of the male palp of Nihonella chika gen. et. sp. nov. A. ♂, paratype (NSMT-Ar 20911), embolic division, ventro-retrolateral view. B. Ditto, frontal view. C. Ditto, dorsal view. D. Ditto, ventral view. E. ♂, paratype (NSMT-Ar 20910), palp under SEM microscope, anteroretrolateral view. F. Ditto, detail of the tip of the prolateral tibial apophysis. Abbreviations: see Material and methods.

Fig. 6. Distribution of Nihonella chika gen. et. sp. nov. in Western Japan. The star refers to the type locality.