1 6 boundaries; systematics 1 7 1 8 2 ABSTRACT 1 9 Synchronous flashing fireflies of the genus Pteroptyx are ubiquitous throughout 2 0Southeast Asia, yet, knowledge on its biodiversity and evolutionary history remains 2 1 lacking. Recent studies have revealed notable population-level phylogeographic 2 2 structure within the P. tener and P. bearni groups in Malaysia, suggesting that cryptic 2 3 species may exist. Additionally, the close morphological and genetic affinity of the 2 4 recently described species P. balingiana to P. malaccae has raised questions about 2 5 its validity. In this study, we assembled the most densely sampled genetic dataset on 2 6Pteroptyx to-date to estimate a comprehensive phylogeny using mitochondrial and 2 7 nuclear DNA and subsequently implemented a suite of distance-, phylogeny-, and 2 8 coalescent-based species delimitation methods to characterize species boundaries 2 9 within the P. tener, P. bearni, and P. balingiana/P. malaccae groups. Using a total 3 0 evidence approach from multiple lines of evidence, we showed that populations of P. 3 1 tener along the west coast of Peninsular Malaysia are sufficiently divergent from 3 2 populations from the east coast and Borneo to warrant specific recognition, despite 3 3