Orphnaecus pellitus Simon, 1892

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 pellitus Simon, 1892

Figs 2 A, B , 3 , 5

Orphnaecus pellitus Simon, 1892 ( Simon 1892: 36; Simon 1903: 956, figs 1106–1107; West et al. 2012: 25, figs 35 a – c; Acuña et al. 2025: figs 15 a, 20 g).

Type material examined.

Syntypes • 1 ♂ 2 ♀♀ MNHN AR 4678 ; Philippines: Luzon Island, Bicol Peninsula, Camarines Sur Province, Libmanan, ‘ Calapnitan Caves’ [ Culapnitan Caves ] (now Libmanan Caves National Park) . (VVW examined syntypes ♂ ♀; A.-E. Leguin sent images of another syntype ♀) (VVW examined syntypes ♂ ♀; A.-E. Leguin sent images of another syntype ♀).

Other material examined.

• 2 ♂♂ 3 ♀♀ 12 j, UST-ARC 0031 –0047; Philippines: Luzon Island, Bicol Peninsula, Camarines Sur Prov., Libmanan, Brgy. Sigamot, Libmanan Caves National Park (Culapnitan Caves), inside Kalangkawan Cave ; 50–300 m horiz. depth, 20 Apr 2023, LA Guevarra, DC Acuña, CN Noriega, JD Fornillos leg. • 4 j UST-ARC 0048 –0051; [same general locality data as for above], inside Alinsanay Cave ; 50 m horiz. depth, [same collection data as for above] • 2 ♂♂ 4 ♀♀ 1 j, UST-ARC 0052 –0058; [same general locality data as for the former], inside Laya Cave ; 30–50 m horiz. depth, 20 July 2023, LA Guevarra, DC Acuña, JD Fornillos leg. ( DCA examined) .

Gene sequence.

GenBank accessions: PP 778304 – PP 778306 and PP 778313 – PP 778315 (non-types).

Troglomorphism. The troglomorphic characters of O. pellitus are presented in Figs 3 , 4 . A noticeable troglomorphic characteristic of O. pellitus is its weakly pronounced ocular tubercles. Adult specimens of O. pellitus have distinctly tiny eyes making interocular distances greater than epigean and troglophilic congeners (Fig. 3 ). The AME and ALE range are 3.01–3.29 and 2.39–3.07, respectively. Lower ALE, as compared to AME, was only observed in O. pellitus but not in its congeners, suggesting that the eye morphology of O. pellitus is different from that of other Orphnaecus species (Fig. 4 ).

The colour of the body integuments of O. pellitus is lighter (brown) than that of other Orphnaecus species we recently collected and examined. The microstructures of the scales are greyish to dark brown and lack the typical purplish to dark blue sheen of the typical epigean Orphnaecus species. Both mature males and females had shorter leg I than leg IV with a leg formula of 4123 and RF ~ 99 (n = 15). The legs were stout and elongated. The tactile setae all over the body and appendages were also noticeably shorter.

Other subterranean adaptations. After subjecting live specimens of O. pellitus to hypoxia, we observed that they took 5–12 min before they completely lost consciousness and became motionless. On the other hand, epigean and troglophile species subjected to the same procedure became unresponsive less than 2 min after exposure to high CO 2 concentrations. Individuals were also observed to recover faster than non-troglobitic congeners, with no fatalities recorded.

Field observations indicate heightened sensitivity to ground movements in the surrounding environment. When the tarantulas were collected in the caves of the LCNP, they quickly retreated into their burrows when approached from more than a meter away, a behavior not observed in epigean species during our field sampling. In the laboratory, these tarantulas demonstrated rapid prey detection and capture behaviour when fed live insects ( Blaptica dubia , Blatta lateralis , and Gryllidae ). The live insects were introduced into their plastic enclosure and as soon as the insects touched the ground of the substrate, the spiders promptly captured their prey without pausing to observe their surroundings consistently. Notably, juveniles could prey on insects three times their body size. These behaviours could be attributed to the increased sensitivity of their ground movement-sensitive clavate trichobothria and their opportunistic instinct towards food in an environment with limited resources.

Remarks.

This study focused only on the troglomorphic characteristics of O. pellitus . Redescription of this species is being conducted in an ongoing study on the revision of the genus Orphnaecus .

Figures

Figure 2. Dorsal habitus of theraphosid species of LCNP A Orphnaecus pellitus, female B mature male C Orphnaecus tangcongvaca sp. nov., holotype female D Orphnaecus libmanan sp. nov., paratype female E holotype male. Note: Size on actual scale.

Figure 3. Anterior carapace of all known Orphnaecus species showing the comparison of ocular tubercles A, B O. pellitus, showing variation in eyes A ♂ UST-ARC 0055 B ♂ UST-ARC 0052 C O. libmanan sp. nov., holotype ♂ UST-ARC 0133 D O. tangcongvaca sp. nov., holotype ♀ UST-ARC 0142 E O. kwebaburdeos, paratype ♂ BPB 2112012-13 F O. adamsoni, holotype ♂ PNM 14889.

Figure 4. Eye indices (AME and ALE) of selected Orphnaecus species. Connecting lines denote the same individual. The ALE and AME diameter of O. pellitus are relatively smaller than its epigean and troglophile congeners and the ALE ≤ AME based on EI values. Note: Eye index is the ratio of the eye diameter of ALE or AME to the length of the carapace.

Figure 5. The heterospecificity of the three species in LCNP is well supported in the phylogenetic analysis, in which divergences started from ~ 41 Ma (Middle Eocene) to ~ 18 Ma (Early Miocene). The estimated divergence time of the COI gene of the different species of LCNP is represented by 95 % confidence intervals (CI), and the time is expressed in million years ago (Ma) (upper corner left). The Timetree was calculated using the Maximum Likelihood (ML) method and has bootstrap values, divergence time estimates, and error bars (pink) representing 95 % CI (upper left). Species divergences in LCNP are highlighted in pale blue in the ML tree and network, and divergences (nodes) of species in LCNP are marked with red dots in the ML tree. The p-distance heatmap matrix (upper right) with genetic distances is expressed in percentage. The generated phylogenetic network of the same COI gene sequences of different Orphnaecus species and outgroups (lower right). The distribution map shows the locations of the analyzed sequences (lower left). Philippine relief map: © 2024 Mapsland.