Systematics and Evolution of Littorina

Snails belonging to the genus Littorina are the familiar periwinkles found on rocky sea shores throughout Western Europe, Scandinavia, North America, Siberia and Japan. Although common and intensively studied, new discoveries over the last three decades have revolutionized knowledge of these animals. Shells of Littorina are remarkable for their extreme variation in shape and colour, which has led to considerable taxonomic controversy. In this volume the complex taxonomy is revised, based on original anatomical studies and recent genetic research. Detailed descriptions of all 19 living and additional fossil species are illustrated by two colour plates, 63 black-and-white plates of shells and radulae, 24 pages of anatomical drawings and 19 distribution maps. The previously bewildering diversity of the shells is resolved to reveal simple, repeated patterns of intraspecific variability. These are explained in terms of life history and gene flow, adaptation to selection by predators and the physical environment, and ecophenotypic influences. Using information from the cladistic analysis of morphological characters, from the fossil record, and from published work on allozyme frequencies and DNA sequences, a detailed species-level phylogeny has been reconstructed. This, together with distributional and ecological data, reveals likely mechanisms of speciation and morphological adaptation. It is shown that the evolutionary radiation occurred largely in the northern Pacific Ocean, and that invasion of the Atlantic took place following the trans-Arctic biotic interchange during the late Pliocene.