Zoma dibaiyin Miller, Griswold & Yin, 2009

Suzuki, Yuya, Hiramatsu, Takehisa & Tatsuta, Haruki, 2022, Two new species and a new genus of ray spiders (Araneae, Theridiosomatidae) from the Ryukyu Islands, southwest Japan, with notes on their natural history, ZooKeys 1109, pp. 67-101 : 67

Zoma dibaiyin Miller, Griswold & Yin, 2009

Figs 4 , 5 , 11 , 12B , 13F-H

Zoma dibaiyin Miller, Griswold & Yin, 2009: 27, figs 10A-F, 11A-B, 13A-D (holotype male and paratypes from China; not examined); Ono and Ogata 2018: 120, 504, 505; Suzuki and Serita 2021 a: 231, figs 1-3.

Material examined.

Japan, Amami Is. (Kagoshima Prefecture): 1♂ 1 ♀ (NSMT-Ar. 21720, 21721), Ôshima District, Setouchi Town, Katsuura (28°12'33.7"N, 129°19'54.0"E, alt. 354 m), 4 Jul. 2021, Y. Suzuki leg. ; 1 ♂ 1 ♀, Amurogama (28°13'15.4"N, 129°18'59.3"E, alt. 111 m), 4 Jul. 2021, Y. Suzuki leg. ; 1 ♂, Amami City, Sumiyo Town, Nishinakama , Santarou-toge Pass (28°15'48.7"N, 129°25'09.0"E, alt. 141 m), 6 May 2021, Y. Suzuki leg. ; Okinawa Is. (Okinawa Prefecture): 1 ♂ 1 ♀, Kunigami District, Ôgimi Village, Nerome (26°40'49.7"N, 128°08'01.1"E, alt. 128 m), 14 Apr. 2021, Y. Suzuki leg. ; Kume Is. (Okinawa Prefecture): 1 ♂ 1 ♀, Shimajiri District, Kumejima Town, Uezu , Mt. Daruma-yama (26°21'42.9"N, 126°45'34.9"E, alt. 149 m), 10 Sep. 2021, Y. Suzuki leg.

Diagnosis.

Males of this species can be distinguished from congeners by the embolic apophysis with a curved tip running along the sclerotized surface of the ventral tegulum, and females by a nearly transverse posterior margin of the epigynal plate (more convex in Z. zoma and rounded in Z. taiwanica ) and lower position of the spermathecae (higher in Z. taiwanica ) ( Miller et al. 2009; Ballarin et al. 2021).

Description.

Male (NSMT-Ar 21720). Measurements. Body 1.62 long. Carapace 0.74 long, 0.68 wide, 0.60 high. Eye size and interdistances: AME 0.090, ALE 0.076, PME 0.093, PLE 0.065, AME-AME 0.015, AME-ALE 0.032, PME-PME 0.008, PLE-PLE 0.070. Leg length: leg I 0.80 + 0.23 + 0.57 + 0.47 + 0.28 = 2.35; leg II 0.50 + 0.21 + 0.46 + 0.31 + 0.28 = 1.76; leg III 0.40 + 0.19 + 0.23 + 0.24 + 0.24 = 1.30; leg IV 0.44 + 0.14 + 0.34 + 0.27 + 0.27 = 1.46. Abdomen 0.88 long, 0.95 wide, 1.01 high.

Carapace oval, longer than wide (CaL/CaW 1.34). Chelicerae with three teeth on promargin. Abdomen oval, wider than long (AL/AW 0.93).

Coloration and markings (Fig. 4A, B ). Carapace, chelicerae, maxillae, labium, sternum, and legs yellowish brown. Eyes on the dark bases. Cephalic groove stained with dark spots. Legs lacking annulation. Abdomen dark brown encircled dorsolaterally with a whitish silver band.

Palp (Figs 4C-H , 5 ). Paracymbium with sharp tip. Tegulum bulbous. Median apophysis weakly sclerotized, wider than long. Embolic division branched into a few bristle-like apophyses, embolus short and tubular, and a long and filiform embolic apophysis emerging beneath from a translucent conductor. Tip of embolic apophysis curved and running along sclerotized surface of the tegulum beneath the conductor. Conductor having two projections: posterior conductor projection strongly sclerotized and triangular with a blunt tip; retrolateral conductor projection strongly sclerotized and weakly curved anteriorly with a triangular posterior tip. Posterior margin of conductor with a sharp tip.

Female (NSMT-Ar 21721). Measurements. Body 2.04 long. Carapace 0.82 long, 0.76 wide, 0.67 high. Eye size and interdistances: AME 0.089, ALE 0.082, PME 084, PLE 0.076, AME-AME 0.023, AME-ALE 0.034, PME-PME 0.009, PLE-PLE 0.076. Leg length: leg I 0.66 + 0.32 + 0.42 + 0.33 + 0.22 = 1.95; leg II 0.64 + 0.30 + 0.41 + 0.33 + 0.21 = 1.89; leg III 0.36 + 0.18 + 0.20 + 0.25 + 0.18 = 1.17; leg IV 0.53 + 0.21 + 0.34 + 0.27 + 0.22 = 1.57. Abdomen 1.21 long, 1.32 wide, 1.16 high.

Carapace, mouthparts, and abdomen as in male (CaL/CaW 1.08; AL/AW 0.92).

Coloration and markings (Fig. 4I ) similar to male.

Genitalia (Fig. 4J, K ). Epigynal plate flat and wider than long with a sclerotized posterior margin and a median pit. Spermathecae touching each other, copulatory ducts wide at their openings, and the course of the ducts simple. See Miller et al. (2009) for further details.

Remarks.

A strongly sclerotized triangular projection with a rounded tip (Figs 4E , 5B ) and a cornered margin of the posterior membrane of the conductor (Figs 4E , 5B , arrowed) were visible in the ventro-posterior view of the male palp. The triangular projection does not seem to be homologous to conductor projection in Theridiosoma , as the former protrudes from the posterior margin of the conductor, while the latter was positioned on the surface of the conductor. Herein, we define it as posterior conductor projection (PCP).

The embolus on the male palp was not determined in Z. dibaiyin and Z. fascia ( Miller et al. 2009; Zhao and Li 2012). In Z. taiwanica , the embolus is described as a 'short and tubular structure’ but lacks explanations in illustrations ( Zhang et al. 2006). Ballarin et al. (2021) determined the embolus as a strongly sclerotized, thin, stick-like apophysis located on the retrolateral side of the embolic division ( Ballarin et al. 2021). Considering the shape of Theridiosoma 's embolus, which is short, tubular, and hidden under conductor (see Coddington 1986a: fig. 131), we suppose the ‘embolus’ of Zoma species determined in Ballarin et al. (2021) is not an embolus. The true embolus of Z. dibaiyin is found beneath basal part of embolic apophyses (Fig. 5D ). Hereafter we defined the sclerotized stick-like structure as a retrolateral conductor projection (RCP), and distinguishable from an embolus. The shape of RCP is useful as a taxonomic character for differentiating species within the genus Zoma : S-shaped with pointed tip in Z. fascia , claviform with rounded tip in Z. taiwanica ( Zhao and Li 2012: figs 28, 30; Zhang et al. 2006: figs 4-6; Ballarin et al. 2021: fig. 5B, C), and weakly curved anteriorly with a triangular posterior tip in Z. dibaiyin (Figs 4D , 5D ).

Distribution.

China (Yunnan), Japan (Honshu to the Ryukyu Islands; Fig. 11 ).

Habitat.

This species inhabits the forest floor and streamside in dim and wet forests (Fig. 12B ).

Web morphology.

This species weaves a concave orb web with radial anastomosis above the ground (Fig. 13F-H ). The orb web is almost horizontal. A tension line stretched from the center of the web and attached to substrates such as rocks and dead leaves. The mesh of sticky spirals tends to be fine (occasionally, the number of sticky lines is> 30). For details of the web morphology, see Hiramatsu (2021).

Egg sac.

light brown with a distinct circular suture at the upper end. The sac was suspended from a long horizontal line with a short stalk (see Hiramatsu 2021).

Figures

Figure 4. Zoma dibaiyin Miller, Griswold & Yin, 2009, male habitus and genitalia (NSMT-Ar 21720 A-H) and female habitus and genitalia (NSMT-Ar 21721 I-K) A habitus, dorsal view B habitus, lateral view C palp, retrolateral view D palp, ventral view E palp, posterior-ventral view F palp, prolateral view G embolic division, prolateral view H embolic division, posterior-ventral view I habitus, dorsal view J epigyne, ventral view K vulva, dorsal view. Abbreviations: C conductor CD copulatory ducts E embolus EA embolic apophysis FD fertilization ducts MA median apophysis PC paracymbium PCP posterior conductor projection RCP retrolateral conductor projection S spermatheca ST subtegulum T tegulum. Arrows in E, F, H indicate a cornered margin of posterior membrane of conductor. Arrow in J indicates a sclerotized median pit. Scale bars: 1.0 mm (A, B, I); 0.1 mm (C-H, J, K).

Figure 5. Zoma dibaiyin Miller, Griswold & Yin, 2009, male genitalia (NSMT-Ar 21720) A ventral view B posterior-ventral view C prolateral view D conductor and embolic division, retrolateral view E conductor and embolic division, posterior-ventral view. Abbreviations: C conductor CD copulatory ducts E embolus EA embolic apophysis MA median apophysis PC paracymbium PCP posterior conductor projection RCP retrolateral conductor projection ST subtegulum T tegulum. Arrows in B-E indicate a cornered margin of posterior membrane of conductor. Scale bars: 0.1 mm.

Figure 11. Distribution of theridiosomatid species in the Ryukyu Islands, Japan.

Figure 12. Habitats of theridiosomatid species in Ryukyu Islands A streamside in dim forest at Iriomote Island B forest floor of secondary forest at Kume Island C grassland at Kume Island D grassland at Yonaguni Island E crevices on limestone rocky wall at Iriomote Island.

Figure 13. Web of Theridiosoma and Zoma spiders at Ryukyu Islands, Japan A-C web of Theridiosoma nigrivirgatum sp. nov. D-E web of Theridiosoma alboannulatum F-H web of Zoma dibaiyin. Abbreviations: RA radial anastomosis SS sticky spirals TL tension line.