Three new species of Onomastus Simon, 1900 (Araneae: Salticidae) from India and Sri Lanka: highlighting the value of collaborative cross-border taxonomic research.

The genus Onomastus represents an ancient, basal lineage of jumping spiders confined to the Oriental region. In this study, three new species, O. brahmagiri Jose & Benjamin, sp. nov. (male, female) and O. silentvalley Jose & Benjamin, sp. nov. (male, female) from India, and O. wijesinghei Benjamin & Jose, sp. nov. (male, female) from Sri Lanka are described. O. patellaris Simon, 1900 is redescribed based on new material. Detailed morphological descriptions, diagnostic illustrations and scanning electron micrographs are provided. Newly described species, along with recently reported species are incorporated into a revised cladistic framework based on 36 morphological characters across 25 taxa. The analysis supports the monophyly of the genus and separates it into South East Asian and South Asian clades. Within the South Asian clade, the Indian species forms a separate monophyletic group and in the South East Asian clade, O. chenae, O. subchenae, O. zhuwu, O. kanoi, and O. complexipalpis form a cluster. This further substantiates the phylogeographic structuring and micro-endemism within South Asian Onomastus. The study highlights the restricted distribution of the genus within the sky islands of the Western Ghats, rendering them particularly vulnerable to rising global temperatures and habitat loss.