Zoma taiwanica Ballarin & Yamasaki & Su 2021, comb. nov.

Zoma taiwanica (Zhang, Zhu & Tso, 2006) comb. nov.

Fig. 5A ̅G.

Theridiosoma taiwanica Zhang, Zhu & Tso, 2006: 265, f. 1̅6 (³♀).

Material examined. TAIWAN: 3♀♀, 3 juv., Taitung County, Orchid Island (Lanyu), Hongtou neighborhood, along the trail to Datianchi lake († R ¨), Elev. 106 m a.s.l., (22°00’46.2”N, 121°34’13.9”E), rainforest litter along the trail, 13. JUNE.2019, (NMNS); 1³, 1♀, 1juv., along the trail to Datianchi lake († R ¨), Elev. 270 m a.s.l., (22°00’59.1”N, 121°34’20.5”E), rainforest litter, 13. VI.2019, (NMNS); 2♀♀, 3 juv. Hongtou forest, walking trail under a bridge, Elev. 68 m a.s.l., (22°00’34.8”N, 121°34’26.1”E), rainforest litter, 17. JUNE.2019, (NMNS); 2♀♀, Dongqing neighborhood, Elev. 50 m a.s.l., (22°01’42.5”N, 121°34’36.4”E), rainforest litter, 14. JUNE.2019, (MSNV); 2³³, 3♀♀, same locality, Elev. 40 m a.s.l., (22°01’47.6”N, 121°34’30.3”E), rainforest litter with many stones, 15.JUN.2019, (FBPC); 2♀♀, 2 juv., Langdao neighborhood, near the Shiaotientci lake, Elev. 160 m a.s.l., (22°04’39.7”N 121°30’35.8”E), rainforest litter, 17. JUNE.2019, (NMNS); 4♀♀, near the Lanyu lighthouse, Elev. 200 m a.s.l., (22°04’53.2”N, 121°30’17.7”E), rainforest litter, 17. JUNE.2019, (NSMT). All leg. Ballarin F.

Diagnosis. Male Zoma taiwanica comb. nov. can be distinguished from male Z. dibaiyin Miller, Griswold & Yin, 2009 by the shorter embolic apophysis (see Fig. 5A, B vs. fig. 10F in Miller at al. 2009), and from male Z. fascia Zhao & Li, 2012 by the different shape of the embolus (straight rather than Z-shaped and with a different tip, see Fig. 5B, C vs. figs. 28C, 30B in Zhao & Li, 2012). Female Z. taiwanica comb. nov. can be separated from female Z. dibaiyin and Z. zoma Saaristo, 1996 by the different, rounded shape of epigynal plate and the higher position of spermathecae (see Fig. 5D, E vs. fig. 11A, B in Miller et al., 2009 and fig. 5 in Saaristo 1996). Apparently, no distinct characters can be found in epigyne and vulva to clearly separate female Z. taiwanica comb. nov. from female Z. fascia.

Description. Habitus of male and female as in Fig. 5F, G. Male palp as in Fig. 5A ̅C. Female epigyne and vulva as in Fig. 5D, E. For a detailed description of male and female see Zhang, Zhu & Tso 2006, p. 265.

Distribution. Southern Taiwan (Pingtung County, Kenting National Park), Orchid Island. Widespread throughout the island. (Fig. 7).

Habitat. Humid rainforest leaf litter.

Remarks. This species was originally described by Zhang et al. (2006) and placed in the genus Theridiosoma O. Pickard-Cambridge, 1879. In the diagnosis, the authors did not discuss the similarities of the new species with the genus Zoma Saaristo, 1996, established on the base of a single species: Zoma zoma Saaristo, 1996 from the Seychelles. Careful examination of samples of Z. taiwanica comb. nov. from Orchid Island, and comparison with the drawings by Zhang et al. (2006) allowed us to identify the diagnostic characters of the genus Zoma in Z. taiwanica comb. nov. Similar characters include a flat, bluntly triangular epigynal plate with a wide and shallow median pit (Saaristo 1996); a filiform embolic apophysis of the male palp extending beyond the conductor tip; an embolic division with moderate, simple branching; silver patches on the abdomen forming a curved transverse stripe; and juxtaposed posterior median eyes (Miller et al. 2009) (see Fig. 5A ̅G). On the base of this evidence, we propose to transfer Theridiosoma taiwanica Zhang, Zhu & Tso, 2006 to the genus Zoma.

A similar species, Z. fascia Zhao & Li, 2012, was described from Hainan Island, China. The diagnosis of this species does not include a comparison with Z. taiwanica comb. nov., which at the time of publication was still included in the genus Theridiosoma. We did not have the opportunity to examine the type specimens of Z. fascia. However, the comparison with the excellent illustrations from Zhao & Li (2012), reveals that the females of Z. fascia and Z. taiwanica are morphologically very similar. We failed to find any discernible diagnostic characters in the shape of the epigynal plate, internal ducts, or position of spermathecae that would allow a clear separation of the two species. Males, on the other hand, show minor differences in the shape of the embolus. Due to only a single male being illustrated in Zhao & Li (2012), we cannot advise if such differences indicate distinct species, or if they are better interpreted as intraspecific variability within a single, widespread species. We are inclined to suggest that the latter is probably the most parsimonious explanation. A direct morphological comparison between a larger number of specimens from Hainan and Taiwan, as well as the use of molecular data, may help to solve this problem in future.