Living members of the tribe Austromegabalanini are large balanid barnacles (Crustacea: Cirripedia: Neobalanoformes) that live in temperate and cold waters of the Southern Hemisphere. During the Neogene, however, the austromegabalanines also inhabited the Northern Hemisphere, as well as some low-latitude tropical environments. This paper describes a new taxon of austromegabalanines, Perumegabalanus calziai gen. et sp. nov., from the shallow-marine, nearshore, lower Miocene (19 to 17 Ma, Burdigalian) deposits of the Chilcatay Formation (East Pisco Basin, southern Peru). Among austromegabalanines, this new taxon is characterised by the presence of thick, ornamented, multitubiferous parietes, where the parietal tubes are irregularly partitioned by auxiliary septa; in addition, the sheath is vesicular. Based on morphofunctional considerations, the peculiar shell architecture of P. calziai is here interpreted as well-suited for an existence in the intertidal zone. In the Chilcatay strata, two taxa of Austromegabalanini (i.e., Austromegabalanus carrioli and P. calziai) coexist, representing some of the geologically oldest records of austromegabalanines worldwide – an observation that strongly supports the hypothesis of a circum-equatorial origin and early diversification for this successful lineage of acorn barnacles.