Orphnaecus tangcongvaca Acuña & Guevarra, 2025

Acuña, Darrell C., Ragasa, Lorenz Rhuel P., Santiago-Bautista, Myla R., von Wirth, Volker & Guevarra Jr, Leonardo A., 2025, Revisiting and rediscovering the tarantulas (Araneae, Theraphosidae) of Culapnitan (Libmanan) Caves in the Philippines: troglomorphism, taxonomy, phylogeny and ecological niche, Subterranean Biology 52, pp. 143-186 : 143-186

Orphnaecus tangcongvaca Acuña & Guevarra sp. nov.

Fig. 9

Orphnaecus sp. “L 4” Acuña et al., 2025.

Type material.

Holotype • ♀ PNM 18869 UST-ARC 0142 , field # CSL 06-02; Philippines: Luzon Island, Bicol Peninsula, Camarines Sur Prov., Libmanan, Brgy. Sigamot, Libmanan Caves National Park; burrows under fallen branch and stones on forest slope near Laya Cave , 20 July 2023, LA Guevarra, DC Acuña, JD Fornillos leg. Paratypes • 3 ♀♀ UST-ARC 0141 , 0143, 0144; [same data as for holotype]. ( DCA examined) .

Type gene sequence.

GenBank accession: PP 778316 (holotype).

Diagnosis.

O. tangcongvaca sp. nov. is placed in Orphnaecus based on its genetic affinity within the Orphnaecus clade and by its spermathecal morphology with lobe converging, slightly pointing inward, and mesoprolaterally concave (Fig. 10 J ) ( Acuña et al. 2025). It is currently the only species that exhibits dwarfism placed in Orphnaecus and has dramatically reduced stridulatory organ (lyra) on the prolateral maxilla (Fig. 10 H, I ). The females further differ from all Orphnaecus species (except O. adamsoni ) by the shape of their female spermathecal lobe, which is broad with its apex slightly narrower than the base but not distinctly narrower than the base (Fig. 10 J ) with SI ~ 90 (n = 4) (SI <65 in all congeners; narrow lobe in O. pellitus ; distinctly narrower apex than the base in O. kwebaburdeos and O. libmanan sp. nov., see Acuña et al. 2025, fig. 18). It also differs from O. libmanan sp. nov. and O. pellitus in having longer tibia I than IV with TBI ~ 105 (n = 4) (TBI ~ 90 in the two other species). It further differs in O. kwebaburdeos and O. libmanan sp. nov. in having shorter tarsus I than IV with TI ~ 91 (n = 4) (TI> 100 in the two other species). It also differs from O. kwebaburdeos for having shorter leg I than IV, with RF ~ 96 (n = 4) in females (I> IV with RF ~ 101 in O. kwebaburdeos female).

Remarks.

The male is unknown. O. tangcongvaca sp. nov. was not distinguished from the females of O. adamsoni since the paratype female is misidentified and misplaced in Orphnaecus (see remarks above).

Description.

Holotype female, PNM 18869 ( UST ARC 0142 , field # CSL 06-02), body length 16.06. (Fig. 9 ).

Prosoma. Carapace (Fig. 10 B ): CL 6.77, CW 4.93, CH 2.00, CR 4.77 long. Ocular tubercle (Fig. 10 D ): 0.95 long, 1.25 wide. Eyes (Fig. 10 D ): anterior row slightly procurved at 168 °, posterior row recurved at 148 °, ALE> AME> PME > PLE, AME 0.33, ALE 0.34, PME 0.32, PLE 0.28. Interocular distances: AME - AME 0.1, ALE - ALE 0.69, PME - PME 0.53, PLE - PLE 0.89, AME - ALE 0.05, AME - PME 0.02, AME - PLE 0.53, ALE - PME 0.24, ALE - PLE 0.14, PME - PLE 0.03. Fovea (Fig. 10 B ): 0.97 wide, procurved, curvature 131 °. Chelicerae (Fig. 10 E – G ): 3.96 long, 2.80 wide, teeth 10 (nine large, one very small), mesoventral denticles ~ 28, cheliceral strikers’ rows of pallid spiniform setae with filiform ends (Fig. 10 G ). Maxilla (Fig. 10 H, I ): 2.23 long, 1.71 wide, maxillary cuspules 187. Lyra (Fig. 10 H ): composed only of a single short and club-shaped stridulatory seta (Fig. 10 H , arrow) (the number could vary when more specimens become available), 0.45 long. Labium: 0.99 long, 1.27 wide, labial cuspules 332, labiosternal sigilla 0.54 long, 0.23 wide, 0.53 apart. Sternum (Fig. 10 C ): 2.89 long, 1.97 wide, anterior sigilla almost round, 0.17 long, 0.15 wide, 1.49 apart, median sigilla ovoid, 0.28 long, 0.17 wide, 1.63 apart, posterior sigilla ovoid, 0.44 long, 0.17 wide, 1.06 apart.

Opisthosoma. Abdomen (Fig. 10 A ): 7.52 long, 4.24 wide, ovular elongated. Spinnerets: PMS, 1.00 long, 0.4 wide, PLS, basal segment 1.23 long, 0.55 wide, median segment 0.72 long, 0.6 wide, apical segment 1.16 long, 0.47 wide.

Genitalia. Spermathecae (Fig. 10 J ): spermathecal lobe 0.52 long, basal width 0.39, distal width 0.35, basally 0.20 apart, unilobed, distally slightly converging, apically slightly pointing inwards, and concave mesoprolaterally.

Legs. Leg formula 4123. Leg lengths (fem., pat., tib., met., tar.): palp 10.56 (3.58, 2.08, 2.52, n / a, 2.38), leg I 16.48 (4.8, 2.72, 4.08, 2.8, 2.08), leg II 14.32 (4.08, 2.48, 3.12, 2.56, 2.08), leg III 11.72 (3.52, 1.56, 2.16, 2.52, 1.96), leg IV 17.12 (5.00, 2.04, 3.88, 3.92, 2.28). Leg widths (fem., pat., tib., met., tar.): palp (1.42, 1.04, 1, n / a, 0.78), leg I (1.64, 1.28, 1.2, 0.88, 0.76), leg II (1.48, 1.2, 1.04, 0.84, 0.64), leg III (1.33, 1.12, 0.88, 0.72, 0.6), leg IV (1.36, 1.16, 1, 0.72, 0.6). Coxae (Fig. 10 C ): (palpcoxa, see Prosoma: Maxilla) Length (coxa I – IV) 2.93, 2.13, 1.87, 2.21. Width (coxa I – IV) 1.33, 1.31, 1.33, 1.44. Trochantera: Length (troch. palp – IV) 0.79, 1.44, 1.31, 1.1, 1.09. Width (troch. palp, I – IV) 1.29, 1.25, 1.15, 1.12, 1.47. Tarsi III and IV with transverse weakening (cracked or bent), tarsi I and II with no visible weakening. Spines: Metatarsal spines (dorsal-ventral), met. I 0–1, met. II 0–3, met. III 2, 3, met. IV. 2, 3. Claws: palp with one claw, tarsi I – III with pair of claws, tarsus IV with unpaired inferior third claw, all claws have no teeth.

Setation. Tactile setae (TS) — brown to pale brown, pallid apically, strong TS covering body and legs, dense on ventral tibia I. Dark spiniform and translucent setae present on all lateral coxae. Femoral setation on femur I sparsely covered with fine needleform setae, intermixed with scales. Scales (SC) — lanceolate SC, reflecting pale brown color, covering all legs, sternum, chelicerae, and spinnerets brown on the entire abdomen. Cottony pale brown SC covering the carapace. Trichobothria — clavate trichobothria present on all tarsi, intermixed with epitrichobothria. Clusters of epitrichobothria are present on all metatarsi, tarsi, and tibiae. Filiform trichobothria are present sparsely on all dorsal legs. Filiform trichobothria present on all dorsal legs, sparsely. Chemosensory sensilla — short, translucent, tapering distally, present singly on the entire body except the carapace and chelicerae. Scopulae — tarsal palp, entire, divided by one or two rows of stiff setae; tar. I, entire, divided by two or three rows of stiff setae; tar. II, entire, divided by two or three rows of stiff setae; tar. III, entire, divided by two or three rows of stiff setae; tar. IV, entire, divided by rows of stiff setae; met. I, almost entire, divided by a row of very sparse long setae; met. II, almost entire, divided by a row of very sparse long setae; met. III, covering 3 / 5, divided by one or two rows of very sparse long setae; met. IV, covering half, divided by two or three rows of sparse long setae.

Color. Entirely uniform brown clothed with brownish setation (Fig. 10 A ).

Indices. CI 72.82, CHI 29.54, CRI 70.46, EI (AME) 4.88, EI (ALE) 5.02, RF 96.26, LI 119.01, TBI 105.16, TI 91.23, SI 89.74.

Male. Unknown. An adult dwarf male was found under the same fallen branch as the holotype female, but managed to escape on the vegetation.

Etymology.

The specific epithet is a noun in apposition in honor of the Tangcong Vaca Guerilla Unit, founded in Camarines Sur and established its base at Tangcong Vaca mountain in Libmanan during the Japanese occupation of the Philippines.

Figures

Figure 9. Orphnaecus libmanan sp. nov., paratype ♀ opisthosoma and genitalia A abdomen, dorsal view B magnified view of the setation on the dorsal abdomen showing two types of setae: tactile setae (TS) and scales (SC) C spermathecae, dorsal view.

Figure 10. Orphnaecus tangcongvaca sp. nov., holotype ♀ A habitus, dorsal view B prosoma, dorsal view C prosoma, ventral view D ocular tubercle, dorsal view E left chelicera, retrolateral view F left chelicera, prolateral view G cheliceral strikers at ventrolateral chelicerae H left maxilla prolateral surface showing a single stridulatory seta (arrow) I left maxilla, prolateral view J spermathecae, dorsal view.