Molecular and morphological characterization of Rhabdias luzonensis n. sp. (Nematoda: Rhabdiasidae) from Sanguirana luzonensis (Boulenger, 1896) (Amphibia: Ranidae) from Luzon Island, Philippines.

A lung-dwelling nematode Rhabdias luzonensis n. sp. is described based on 6 specimens collected from the Luzon frog, Sanguirana luzonensis, on Luzon Island, Philippines. The new species is readily distinguishable from congeneric nematodes occurring in eastern and south-eastern Asia by the very distinct structure of the buccal capsule which consists of anterior thick-walled portion and posterior thin-walled portion; both parts are similar in length. Rhabdias luzonensis is the third species of the genus described from Philippines and the first species described from amphibians of this archipelago. Phylogenetic relationships of the new species and other Rhabdias spp. have been studied using nuclear rDNA (ITS region + partial 28S gene). Our phylogenetic analysis placed the new species in a clade containing several species originating from disparate geographic regions and demonstrating apparent widespread evolutionary host-switching among several families and even orders of amphibians. Given our discovery of the first Rhabdias specific to Philippine frogs, the remaining 120 species of amphibians (∼80 % endemic) native to this archipelago should be the focus of targeted surveys aimed at characterizing undocumented helminth diversity during future field studies. Partial sequences of mitochondrial cox1 and 12S genes have been generated for the new species and several phylogenetically and geographically closest congeners for the purpose of species differentiation and facilitate molecular species identification in future surveys of Rhabdias biodiversity in the Philippines and other SE Asian archipelagos.