Quantitative shape analysis as a diagnostic and prescriptive tool in determining Fragilariforma (Bacillariophyta) taxon status

Abstract

For 120 specimens and figures of Fragilariforma, 10 Legendre coefficients were calculated as shape descriptors. For each half valve apically bisected, 50 x,y coordinates were used to calculate Legendre coeffi cients. Principal components analysis (PCA) was used to ordinate the shape descriptors as a total shape gradient of valve forms. The first four principal components explained 90.3 % of total shape variation. Ten shape groups were circumscribed based on clustering in shape space, and designated taxonomic names were used as a guide. Multiple discriminant analysis cross-validated results from PCA in that no specimen misclassifi cations occurred. Along with historical taxonomic information, shape analysis was used as a tool in diagnosing taxon identifi- cations and prescribing where additional investigation is still necessary. Taxonomic status of Fragilariforma constricta, F. constricta f. stricta, and F. lata was evaluated based on shape group results. Results from shape group analysis indicated Fragilariforma constricta/F. constricta f. stricta shape groups may encompass two different species groups. Fragilariforma lata shape groups also may comprise two different species groups. During the course of this study, it was found that the nomenclature of Fragilariforma hungarica var. tumida is questionable and in need of revision. Overall, shape analysis produced biologically meaningful results and was used as a diagnostic and prescriptive tool in combination with descriptive taxonomic history for taxa in Fragilariforma.