A new species of Tithaeidae (Arachnida: Opiliones: Laniatores) from Mindanao reveals contemporaneous colonisation of the Philippines by Sunda Shelf opiliofauna

Abstract

The Philippine archipelago harbours a remarkable diversity of harvestmen, with respect to both taxonomy and complexity of biogeographic origins. Among the armoured harvestmen (suborder Laniatores), six families of distantly related groups occur in this archipelago. Here, we describe a new species of the family Tithaeidae, Tithaeus odysseus sp. nov., discovered during a collecting campaign on the island of Mindanao. The description of this species expands the known distribution of the family and demonstrates another exception to the zoogeographic boundary known as Huxley’s Line which putatively separates the biota of the Philippines (excluding the Palawan island group) from the Sunda Shelf biota. Given the coincident distributions of Tithaeidae and the mite harvestman family Stylocellidae (Cyphophthalmi), a group renowned for its poor dispersal ability, we inferred phylogenetic relationships and divergence times of the Philippines lineages of both families by using a comprehensive molecular dating analysis of all Opiliones. The internal phylogeny of Tithaeidae mirrored the biogeography of Philippine Stylocellidae, showing a close affinity between the Philippine and Bornean species. Molecular dating showed contemporaneous colonisation of Mindanao by both families in the Cretaceous. We infer these patterns to reflect faunal connections between the southern Philippines and Borneo via the Zamboanga Peninsula. To render the genus Tithaeus monophyletic, we synonymise Metatithaeus with Tithaeus (new synonymy).