Morphometrics Suggest Reduced Diversity in the Freshwater Snail Genus Gyrotoma Shuttleworth, 1845 (Gastropoda: Pleuroceridae)

ABSTRACT Alabama has long been recognized as an aquatic biodiversity hotspot, and the Coosa River was home to over 80 endemic freshwater snail species. Due to human activity, over 40% of the snails have been extirpated, including the pleurocerid genus Gyrotoma Shuttleworth, 1845. Gyrotoma species varied in terms of shell shape and sculpture and were restricted to certain reaches of the Coosa River. Diversity estimates based on shell morphology have ranged from 44 nominal taxa to the modernly recognized six Gyrotoma species. However, basing pleurocerid species boundaries on qualitative morphological features poses many taxonomic and systematic issues. To better estimate diversity in the genus, geometric morphometrics and Gaussian mixture models were used to assign individual Gyrotoma shells to one of three clusters. Individuals in each cluster had significantly different shapes along with different combinations of quantifiable shell traits. No specific distributional patterns were observed between clusters. Though each cluster was not assigned to any specific taxonomic unit, morphometrics suggested a significant reduction in the number of Gyrotoma taxa. The clusters presented represent testable hypotheses of possible Gyrotoma diversity for when additional data are available.