ABSTRACT Cirripedes of the superorder Acrothoracica are normally found as epizoic borings on marine calcareous substrates. Armatoglyptes taiwanus (Utinomi, 1950) is a lithoglyptid acrothoracican barnacle reported from different parts of the Indo-Pacific. Recent studies have demonstrated phylogenetic breaks between the Indian and Pacific Oceans populations in widespread Indo-Pacific marine organisms due to isolation events during the Pleistocene glaciations. It is possible that A. taiwanus represents a cryptic species complex in the Indo-Pacific, which the previous studies have failed to identify from morphology alone. In the present study, we analyzed the morphology and the sequence divergence of the 12S rDNA of A. taiwanus from the Indo-Pacific region, including Taiwan and the Philippines in the Pacific, and Phuket Island (Thailand) and the Mozambique Channel in the Indian Ocean, to test whether A. taiwanus is a cryptic species across its geographical range. The results showed that A. taiwanus has a homo...