Morphological shell characterization of Fissurellidea and Fissurella (Vetigastropoda: Fissurellidae) along the Argentinean coast, from temperate to subantarctic waters

Abstract

Morphometric studies are approached through different methods, among them geometric morphometry, such as contours and landmarks. These methodologies gathered with classification methods, such as linear discriminant analysis (LDA) and principal component analysis (PCA), extract information efficiently and capture inter or intraspecific grouping. Three keyhole limpet species—Fissurellidea megatrema, Fissurellidea patagonica, and Fissurella radiosa—were contrasted through morphometrics: shell shape with linear morphometrics and foramen shape through elliptic Fourier analysis, and landmarks. The broad geographic range of F. radiosa allowed additional intraspecific analysis: three sampling sites, along the Southwest Atlantic coast (42°19′S 64°19′W–54°48´S 68°19′W), comprising two subspecies (F. radiosa radiosa and F. radiosa tixierae). The aim of this study was to evaluate which measurements most contribute to the classification of the species and to determine if the subspecies reflected a geographic pattern in the classification methods (LDA and PCA). The LDA revealed two linear morphological variables to differentiate between the three species and between localities of F. radiosa. For the subspecies (F. radiosa radiosa and F. radiosa tixierae), the LDA and PCA showed a biogeographic pattern related to the distribution (Argentinean and Magellan provinces). We concluded that the morphometrics methods and both classification analysis (LDA and PCA) capture information at the species and subspecies level and the foramen is the principal variable that contributes as a taxonomic tool.