Howaia alba, 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

Howaia alba sp. nov.

Figs 2A-J , 4E-H , 15C , 16B (Japanese name: tsuzupisuki-horahimegumo ツヅピスキホラヒメグモ)

Nesticella mogera Shimojana 1977: 353, fig. 6 (♂, misidentification).

Type material.

♂ Holotype (NMST-Ar. 25251): Japan: Okinawa Pref.: Miyako-jima Is.: Shimozato Hirara, Oharaminami Park, Tsuzupisuki-abu cave (ツヅピスキアブ), 32 m, long and humid cave, in the dark zone of the cave, 24.79468°N, 125.28192°E, 12.Nov.2020, F. Ballarin leg.

Paratypes: Japan: Miyako-jima Is.: 3♀, same data as the holotype (NSMT-Ar 25252); 1♀, same locality 14.Nov.2020, F. Ballarin leg. (RMUF); 5♀, same locality, 16.Sep.2022, F. Ballarin leg. (2♀ MNHAH, 3♀ FBPC); 4♀, Nobaru Ueno, Pinza-abu cave (ピンザアブ洞穴), 57 m, long and muddy cave, in the dark zone of the cave, 24.74853°N, 125.33443°E, 13.Nov.2020, F. Ballarin leg. (RMUF); 3♀, same locality, 17.Sep.2022, F. Ballarin leg. (FBPC).

Other material examined.

Japan: Miyako-jima Is.: 1 juv., Nakabari, Nakabari Limestone Cave (仲原鍾乳洞), 24.73384°N, 125.37610°E, 29.Dec.2021, R. Miyata leg. (FBPC) .

Etymology.

The specific name is derived from the Latin word for the color white (albus, adjective) referring to the whitish coloration of the species.

Diagnosis.

The new species is similar to H. mogera and to the troglobitic species H. rongtangensis (Lin, Ballarin & Li, 2016) from Hainan Island, H. subterranea sp. nov., and N. occulta sp. nov. Male of H. alba sp. nov. can be distinguished from male of H. mogera and H. rongtangensis by the different shape of the larger paracymbium (P) bearing a longer, slimmer, and sharper distal process (Di) (vs slimmer P with a shorter, larger, and blunter Di in H. mogera and H. rongtangensis ) (Figs 2A-D , 4E-G cf. Figs 1A-D , 4A-C and Lin et al. 2016: fig. 44A, B, D). Female of the new species are distinguished from female of H. mogera , H. subterranea sp. nov., and N. occulta sp. nov. by the larger and stockier scapus (Sc) with a slightly rounded posterior margin (vs slimmer Sc with a flat posterior margin in H. mogera , a longer Sc with a wider lobated tip in H. subterranea sp. nov., and a slimmer, tongue-like Sc ending with a strongly concave tip in N. occulta sp. nov.) (Figs 2E-G , 4H cf. Figs 1E-G , 3D, E , 4D , 11C, D , 13E, F ).

Description of male

(holotype). Habitus as in Fig. 2H . Total length 1.88. Prosoma 0.94 long, 0.83 wide. Carapace uniformly pale yellowish. Eyes completely degenerated and reduced to white maculae. Cervical groove and fovea indistinct. Chelicerae brownish. Labium, maxillae, and sternum of the same pale color as carapace. Legs uniformly pale yellowish. Leg formula: I, IV, II, III. Legs measurements as follows: I 6.17 (1.61, 0.47, 1.60, 1.72, 0.77), II 4.71 (1.32, 0.39, 1.20, 1.18, 0.62), III 3.89 (1.11, 0.31, 0.95, 1.02, 0.50), IV 5.17 (1.50, 0.37, 1.34, 1.31, 0.65). Opisthosoma uniformly greyish-yellow, covered with long, sparse hairs.

Male palp as in Figs 2A-D , 4E-G . Cymbium relatively elongated, covered with thin sparse setae, bearing some thicker setae on the distal-prolateral margin (Fig. 2D ). Paracymbium with a single distinctly sclerotized, stocky distal process (Di), slightly elongated near the tip and a single sharp, spine-like ventral process (Ve) (Figs 2A-D , 4E-G ). Embolus (E) long and filiform, origin of embolus positioned at ~ 6:00 o’clock on radix (Rx). Radical apophysis (Ra) broad, with a granulate surface. Conductor with 3 distinct processes (Cp, Cr, Cm) and a half-transparent distal lobe (Cl). Prolateral process of the conductor (Cp) flat, ribbon-like and headed counterclockwise, wrapped around embolus. Retrolateral process of conductor (Cr) wide and thick, curved internally, with a broadened, flat central part. Median process of conductor (Cm) stout, horn-like, strongly sclerotized bearing a smaller, stout ventral process. (Figs 2A-C , 4E, F ).

Description of female

(one of the paratypes). Habitus as in Figs 2I , 15C . Total length 2.3. Prosoma 1.09 long, 0.92 wide. Cephalic area as in Fig. 2J . Coloration and other details as in male. Legs measurements as follows: I 6.56 (1.83, 0.50, 1.74, 1.67, 0.82), II 5.09 (1.46, 0.42, 1.27, 1.22, 0.72), III 4.09 (1.31, 0.36, 0.90, 0.92, 0.60), IV 5.46 (1.65, 0.45, 1.42, 1.27, 0.67).

Epigyne and vulva as in Figs 2E-G , 4H . Scapus (Sc) short and stumpy, approximately as long as wide, ending with a slightly rounded posterior margin (Figs 2E, F , 4H ). Copulatory opening (Co) at the inner-lateral sides of scapus. Internal ducts slightly visible through the transparent tegument, shaped as a narrow V. Copulatory ducts (Cd) short and thick, slightly divergent to each other, slightly twisted in the inner trait with 1 coil, curving outward and then inward before reaching the spermathecae. Insemination ducts (Id) thin, coiled around the Cd). Spermathecae (S) small and rounded, separated from each other by ~ 2 × their diameter (Fig. 2G ).

Size variation.

Female (based on 5 specimens): total length: 2.00-2.67, prosoma length: 1.05-1.12, prosoma width: 0.92-0.97.

Distribution.

Endemic to Miyako-jima Is., Ryukyus, Japan (Fig. 16B ).

Habitat and ecology.

Howaia alba sp. nov. is found in the natural caves in Miyako-jima Is. This species builds simple scaffold webs between rocks and in crevices at the base of the walls or on the floor of the caves. It dwells exclusively in the dark zone of the caves, in areas characterized by relatively high and uniform temperature and humidity (e.g., Tsuzupisuki-abi cave: temp: 25.2 °C, hum: 94.1%; Pinza-Abu cave: temp: 25.1 °C, hum: 92.6%) (Fig. 15G ). Adults of Howaia alba sp. nov. were observed preying on Schizomida ( Bamazomus siamensis (Hansen, 1905) which roam the floor of the caves in Miyako-jima Is. Females carrying the eggs cocoon attached to their spinnerets were also observed (but not collected) sitting on webs or wandering under rocks. Despite extensive surveying, no specimens were found in the numerous artificial tunnels or underground water reserves dug in the limestone rocks of the island. The complete absence of eyes and pigmentation, the lack of external records and the finding of the species only in the deepest areas of the caves identify H. alba sp. nov. as a true troglobiont.

Remarks on misidentifications.

This species was recorded and illustrated for the first time by Shimojana (1977: fig. 6A-C). Due to the general similarities in the shape of genitalia, it was identified as H. mogera although the author highlighted the lack of eyes in these specimens ( Shimojana 1977: 353). Our analysis, based on both morphology and molecular data, supports H. alba sp. nov. as a closely related species but clearly distinct from H. mogera .

Figures

Figure 1. Howaia mogera A male palp (holotype), ventral view B same, retrolateral view C same, ventro-prolateral view D same, dorsal view E female epigyne ventral view (specimen from Tokyo area) F same after dissection, shape variation G vulva, dorsal view H habitus of male (specimen from Tokyo area) I habitus of female J cephalic area of female, frontal view. Abbreviations: Cd - copulatory duct; Co - copulatory opening; Id - insemination duct; S - spermatheca; Sc - scapus. Scale bars: 0.2 mm (A-G, J); 1.0 mm (H, I).

Figure 2. Howaia alba sp. nov. A male palp (holotype), ventral view B same, retrolateral view C same, ventro-prolateral view D same, dorsal view E female epigyne (one of the paratypes), ventral view F same, shape variation G vulva, dorsal view H habitus of male (holotype) I habitus of female (one of the paratypes) J cephalic area of female, frontal view. Abbreviations: Cd - copulatory duct; Co - copulatory opening; Id - insemination duct; S - spermatheca; Sc - scapus. Scale bars: 0.2 mm (A-G, J); 1.0 mm (H, I).

Figure 3. Howaia subterranea sp. nov. A habitus of female (holotype) B cephalic area of female, frontal view C habitus of female, lateral view D female epigyne, ventral view 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 4. Genitalia of Howaia mogera and H. alba sp. nov. A male palp of H. mogera, ventral view B same, retrolateral view C detail or paracymbium, dorsal view E female epigyne, ventral view E male palp of H. alba sp. nov., ventral view F same, retrolateral view C detail or paracymbium, dorsal view H female epigyne, ventral view. Abbreviations: Cl - lobe of conductor; Cm - median process of conductor; Co - copulatory opening; Cp - prolateral process of conductor; Cr - retrolateral process of conductor; Di - distal process 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 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).