Revisiting and rediscovering the tarantulas (Araneae, Theraphosidae) of Culapnitan (Libmanan) Caves in the Philippines: troglomorphism, taxonomy, phylogeny and ecological niche

In 1892, French naturalist Eugène Simon described samples of cave-dwelling tarantula species collected from Culapnitan Caves in the Philippines, a cave system that is now part of the present-time Libmanan Caves Natural Park (LCNP). One of these is the new monotypic tarantula genus and species of that time, Orphnaecus pellitus Simon, 1892. Based on Simon’s notes and quick observation of the eyes of the syntypes, this species is highly suspected to be troglobitic.

In the present study, we rediscovered O. pellitus from its reported site and investigated its troglobitic characteristics. Morphological analysis of O. pellitus shows troglomorphic characteristics which include reduced eye size, attenuated limbs, shortened tactile setae, and diminishing pigmentation. Tolerance to hypoxia and heightened sensitivity to ground movements are the other subterranean adaptations that were observed.

Phylogenetic analysis revealed a cladistic relationship among tarantula morphologically identified from the genus Orphnaecus. Our findings provide evidence that O. pellitus is a true troglobitic tarantula reported worldwide, and currently the only one known from Asia. We also report two new species of Orphnaecus, Orphnaecus libmanan sp. nov. and the dwarf Orphnaecus tangcongvaca sp. nov., collected from the forest grounds of the LCNP.

The ecological niche differentiation of theraphosid species in the LCNP is also provided. Our findings are supported by morphology, molecular phylogeny, and ecology.