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.

Complex patterns of Gondwanan biogeography revealed in a dispersal‐limited arachnid

“…The Crozet Islands have never had a continental connection and are volcanic in origin, with the oldest islands being <9 Ma (Meyzen et al, 2016). The relationship of Promecostethus to other triaenonychid genera is uncertain, and several hypotheses have been put forth, including relationships to taxa from South America, Australia, and New Zealand (Forster, 1954; Hickman, 1939; Maury, 1990), an uncertainty that persists even after more detailed morphological examinations (Porto & Pérez‐González, 2020). Derkarabetian et al (2021) hypothesized that the Crozet Islands endemic is derived from Australian taxa, suggesting east to west dispersal.…”

Harvestmen in the first twenty years: a scientometric analysis of Zootaxa’s contribution to opilionology (Arthropoda, Arachnida, Opiliones)

“…The sole paper published on harvestmen from the Antarctic realm (Fig. 6) was a redescription of Promecostethus unifalculatus Enderlein, 1909, by Porto & Pérez González (2020 in Volume 4861, No. 1.…”