USING SHELL PARAMETERS AS COMPLEMENTARY DATA IN PHYLOGENETIC SYSTEMATIC ANALYSES - EVOLUTION OF FORM IN 5 SPECIES OF LITTORINIDS (MOLLUSCA,GASTROPODA)

Gastropod shells contain records of ontogeny and so, house a wealth of biological information. In this paper, I present a methodology for th e analysis of shell forms which yields data that may be used in phylog enetic systematic analyses. I use a mathematical model which considers two aspects of a shell's aperture throughout growth, the ''aperture t rajectory'' and the ''aperture scaling,'' to describe shell shape and size. The aperture trajectory describes the path in space followed by the center of the aperture from the apex to the final lip of a shell, while the aperture scaling represents the changes in the dimensions of the aperture along the trajectory. I treat each whorl of a shell as a separate entity, consider horizontal and vertical components of the t rajectory and scaling as characters, code character states in a conser vative manner, and use them in a cladistic analysis. As an example, I apply the method to shells of five species of periwinkles (Gastropoda: Littorina). I obtain a phylogeny (interpreted cladogram) that differs from recently published hypotheses derived from other types of data, and I compare, contrast, and combine my results with these. Finally, I discuss the assumptions and limitations of the methodology I present.