Changes in the Barnacle Fauna Since the Miocene and the Infraspecific Structure of Tetraclita in Japan (Cirripedia; Balanomorpha)

A zone formed by converging warm and cold oceanic currents along the coast of Japan constitutes a biogeographical barrier separating warm and cold water communities. Historically there have been changes in distribution as well as in paleogeographic composition through immigration and extinction of certain barnacle species, and these changes indicate that there have been latitudinal fluctuations of this zone apparently in response to paleoclimatic changes in the northwest Pacific since the Miocene. The ranges of cold water species extended further south between the early Middle Miocene and Pliocene due to lower temperatures. During interglacial stages of the Pleistocene, warm water species of embayment, intertidal and sublittoral zones, migrated northward with warm currents to inhabit expanding shallow water regions produced by rising sea level. The present-day cold and warm water barnacle species became established in the Pliocene and Pleistocene, respectively. The extinction of species, migration of species into vacant niches, speciation, evolution and infra-specific taxonomy of Tetraclita squamosa are discussed in terms of their morphology, ecology, and distributions in time and space.