Troglotheridion, Hu & Liu, 2025

Hu, Changhao & Liu, Jie, 2025, A new troglobitic genus of the family Theridiidae Sundevall, 1833 (Araneae: Theridiidae) from China, Zootaxa 5627 (2), pp. 387-400 : 388-389

Genus Troglotheridion gen. nov.

Type species. Troglotheridion lamellatum sp. nov..

Etymology. The generic name is a combination of Troglobiont (referring to the cave habitat) and Theridion (type genus of the subfamily Theridiinae , referring to this new genus belongs to the subfamily Theridiinae ). The gender is neuter.

Diagnosis. Troglotheridion gen. nov. resemble those of Takayus Yoshida, 2001 in having thick embolus (E) almost as wide as palpal tibia, and epigyne with sclerotized posterior margin ( Figs 2 , 3 , 5 , 6 vs. figs 41, 52, 54 in Chikuni 1989; figs 80B‒E, 83B‒E, 93B‒E, 94B‒E, 108B‒E, 114B‒F, 115B‒E, 116B‒E, 117B‒E, 118B‒E, 119B‒E, 120B‒D, 125B‒C in Zhu 1998; figs 2‒6 in Yoshida 2001; fig. 1 in Baba & Tanaka 2019; figs B296b, B 297 in Vanuytven 2021; fig. 25A, B in Zhang et al. 2022), but they differ by 1. habitus pale yellow, without patterns (vs. with bright color and dark brown fleck in Takayus ); 2. eyes vestigial (vs. eight eyes present in Takayus ); 3. tegular apophysis (TA) longitudinally elongate (vs. indistinct in Takayus ); 4. conductor (C) elongate and distinct (vs. indistinct in Takayus ); 5. epigyne without scapus (vs. with a distinct scapus in Takayus ); and 6. fertilizated ducts (FD) arising from center of spermathecae (S) (arising from posterior part of spermathecae (S) in Takayus ).

Troglotheridion gen. nov. also resemble that of Yunohamella Yoshida, 2007 in the conductor (C) conjugating with tegulum (T) ( Figs 2 , 3 , 5 , 6 vs. figs 57, 63, 64 in Chikuni 1989; figs 107‒109 in Gao & Li 2014; figs 37‒39 in Marusik & Logunov 2017; figs 3E‒G, 4A in Lee & Kim 2021; figs B2336a, b, B 337 in Vanuytven 2021; figs 1, 3, 5A, B, 6A, B, 7A‒C, 9A‒C in Zhong et al. 2025), but they differ by 1. habitus pale yellow, without patterns (vs. habitus dark with distinct red to dark brown cardiac pattern in Yunohamella ); 2. eyes vestigial (vs. eight eyes present in Yunohamella ); 3. palpal tibia longer or almost as long as cymbium (vs. almost half the length of cymbium in Yunohamella ); 4. tegular apophysis (TA) longitudinally elongate (vs. horizontal in Yunohamella ); 5. embolus (E) thick, almost as wide as palpal tibia (vs. thin in Yunohamella ); and 6. copulatory openings adjacent (vs. separated in Yunohamella ).

Description. Tiny to small sized spiders with total length between 1.59‒2.40. PME absent, AME reduced or absent, ALE and PLE strongly reduced. Carapace and sternum pale yellow. Chelicerae pale yellow, with one promarginal tooth, without retromarginal tooth. Legs pale yellow and haired. Leg formula: I-II-IV-III. Abdomen haired, dorsum with a white mark in front of spinnerets. Prosomal stridulatory ridges and abdominal stridulatory pick rows present in male, absent in females. Prosomal stridulatory ridges long and continuous; two stridulatory pick rows placed dorsally relative to the pedicel on the abdomen. Colulus absent ( Figs 1 , 2 , 5 ).

Palp: Tibia longer or almost as long as cymbium, without prolateral trichobothria (Tb), with two retrolateral trichobothria (Tb). Cymbium kidney-shaped, cymbial hood (Chd) narrow, located at distal cymbium; tarsal organ (TO) enlarged, almost three times the diameter of setal sockets. Subtegulum (ST) bowl-shaped. Tegulum (T) ventrally narrow, retrolaterally with an apophysis (TRA), sperm duct (SD) in prolateral tegulum (T) thick, while retrolateral tegulum (T) thin. Median apophysis (MA) wide, irregular shaped and unbranched. Tegular apophysis (TA) longitudinally elongate, almost as long as embolus (E). Conductor (C) elongate, conjugating with tegulum (T). Embolus (E) drop-shaped, short and thick, prolateral embolus (E) with a triangular projection (EP I), retrolateral embolus (E) with two projections (EP II, EP III) ( Figs 3A‒C , 4 , 6A‒C ).

Epigyne: Epigyne with a slightly sclerotized posterior margin. Copulatory openings adjacent. Copulatory ducts (CD) V-shaped. Fertilizated ducts (FD) curved, branched and arising from center of spermathecae (S) ( Figs 3D‒F , 6D‒F ).

Composition. Troglotheridion lamellatum sp. nov. and Troglotheridion sangzhiense ( Zhu, 1998) comb. nov.

Relationships. In Liu et al. (2016), Theridion sangzhiense was placed in the subfamily Pholcommatinae Simon, 1894 , but this species does not conform to all the characteristics of Pholcommatinae , including: an upward pointing cymbial hook located on the ectal margin, a grooved tegular apophysis (TA), portions of embolus (E) spiral enclosed entirely within tegular apophysis (TA), and the embolic base shifted ectally and partially hidden by cymbium ( Agnarsson 2004). Thus, we consider Theridion sangzhiense in Liu et al. (2016) was probably misidentified.

The two species of this genus exhibit all the characteristics of Theridiinae , including the reduction of prolateral trichobothria (Tb) on the male palpal tibia, epiandrous gland spigots spread over genital plate, and the absent of colular setae ( Agnarsson 2004). Agnarsson (2004) noted that the reduction of retrolateral trichobothria (Tb) on the male palpal tibia occurs within the subfamily, though some reversals exist (with two trichobothria (Tb)), such as in Nesticodes Archer, 1950 and Parasteatoda Archer, 1946 . The two species of the genus Troglotheridion also exhibit two retrolateral trichobothria (Tb) on the male palpal tibia. Therefore, we consider this genus to clearly belong to the subfamily Theridiinae .

Distribution. China (Caves of Yunnan-Guizhou Plateau).

Figures

FIGURE 1A‒D. A posterior margin of carapace of male Troglotheridion lamellatum sp. nov., showing prosomal stridulatory ridges; B anterior abdomen of male T. lamellatum sp. nov., showing stridulatory pick rows; C eye area of male T. lamellatum sp. nov.; D eye area of male T. sangzhiense (Zhu, 1998) comb. nov.. Scale bars: 0.1 mm. Abbreviations: ALE = anterior lateral eye; AME = anterior median eye; PLE = posterior lateral eye.

FIGURE 2A‒D. Troglotheridion lamellatum sp. nov., habitus. A male, dorsal view; B male, ventral view; C female, dorsal view; D female, ventral view. Scale bars: 0.5 mm.

FIGURE 3A‒F. Troglotheridion lamellatum sp. nov. A‒C Left male palp (A prolateral, B ventral, C retrolateral); D epigyne, ventral view, uncleared; E epigyne, ventral view; F vulva, dorsal view.Scale bars:0.1 mm (A‒C), 0.05 mm (D‒F).Abbreviations: C = conductor; CD = copulatory duct; E = embolus; EP I = embolic projection I; EP II = embolic projection II; EP III = embolic projection III; FD = fertilization duct; MA = median apophysis; S = spermatheca; SD = sperm duct; ST = subtegulum; T = tegulum; TA = tegular apophysis; Tb = trichobothria; TO = tarsal organ; TRA = tegular retrolateral apophysis.

FIGURE 4A‒B. Left male palp of Troglotheridion lamellatum sp. nov. A expanded, dorsal; B cymbium, ventral. Scale bars: 0.05 mm. Abbreviations: C = conductor; Chd = cymbial hood; E = embolus; MA = median apophysis; ST = subtegulum; TA = tegular apophysis.

FIGURE 5A‒D. Troglotheridion sangzhiense (Zhu, 1998) comb. nov., habitus (male abdomen missing). A male, dorsal view; B male, ventral view; C female, dorsal view; D female, ventral view. Scale bars: 0.5 mm.

FIGURE 6A‒F.Troglotheridion sangzhiense (Zhu, 1998) comb. nov. A‒C left male palp (A prolateral, B ventral, C retrolateral); D epigyne, ventral view, uncleared; E epigyne, ventral view; F vulva, dorsal view. Scale bars: 0.1 mm (A‒C), 0.05 mm (D‒F). Abbreviations: C = conductor; CD = copulatory duct; E = embolus; EP I = embolic projection I; EP II = embolic projection II; EP III = embolic projection III; FD = fertilization duct; MA = median apophysis; S = spermatheca; SD = sperm duct; ST = subtegulum; T = tegulum; TA = tegular apophysis; Tb = trichobothria; TO = tarsal organ; TRA = tegular retrolateral apophysis.