Redescription of Promecostethus unifalculatus, the only known harvestman from Crozet Islands (Opiliones: Triaenonychidae)

Abstract

Promecostethus unifalculatus Enderlein, 1909, is the only representative of the order Opiliones from the Crozet Islands. The species belongs to the family Triaenonychidae and is biogeographically interesting because it is a candidate for transoceanic dispersal, a very rare event in this ancient family. Despite this significance, P. unifalculatus is taxonomically still poorly known, and a redescription of this species using modern taxonomic standards is urgently needed. Here we redescribe the species, offer the first description and illustrations of the male genitalia and provide a full exomorphological survey of the species using scanning electron microscopy. Furthermore, we provide an emended diagnosis for the genus Promecostethus and discuss its relationship with some morphologically similar genera.