Small, flat, and gray: Cryptic diversity in chthamalid barnacles in the global context of marine coastal biogeography (Cirripedia: Balanomorpha: Chthamalidae)

Abstract

Abstract In the past 40 years, the ability to distinguish phenotypically similar species by using molecular methods has rapidly changed the study of taxonomy, biogeography, and community diversity. A cosmopolitan family of acorn barnacles, Chthamalidae Darwin, 1854, can be found on almost every non-boreal coast, with very similar habitat requirements, larval life histories, and external (test) morphologies among its species. Here I review how molecular methods have aided the description of new species as well as the characterization of phylogenetic diversity within species, and also broadened our understanding of the biogeography of this family. Multiple regional analyses have shown that the coastal habitat appears to drive diversity and diversification in generally similar ways regardless of location, while a global perspective allows us to identify regions and questions that merit further study. Variation in the spatial patterning of genomic diversity among species sometimes provides evidence as to how key life history parameters determine responses of species to ocean currents and forcing, thermal environments, and competition.