MORPHOMETRIC ANALYSIS OF ASTARTE (BIVALVIA: ASTARTIDAE) FROM THE ATLANTIC COASTAL PLAIN

The Atlantic Coastal Plain has long been recognized as a natural laboratory useful for testing hypotheses about various environmental and ecological effects on marine fauna. A reliable taxonomy for genera within the Atlantic Coastal Plain would allow these studies to be conducted rigorously, and produce easily repeatable results. The bivalve genus Astarte, from the family Astartidae, has many species that have been formally named and identified. However, previous work has noted a lack of diversification within the genus and anecdotal evidence suggests that some species lack true morphological separation, with individuals possessing intermediate morphologies. Bivalves, such as Astarte, have complex morphologies and yield numerous landmarks, making them good candidates for a study using geometric morphometrics to discriminate morphospecies.

A preliminary dataset of 46 shells from the Florida Museum of Natural History, representing four different species from the Pliocene of the Atlantic Coastal Plain, were digitally imaged. A total of 6 landmarks and 4 pseudo-landmarks were collected using the program ImageJ. Procrustes analysis was performed to align and resize all individuals for multivariate analysis. Principle Components Analysis was conducted on the Procrustes coordinates, with PC1 and PC2 accounting for 51.4% of variation. These preliminary results show the different species occupying their own morphospace with some slight overlap between three of the four species. Astarte concentrica shows the most variability relative to the other species. Astarte concentrica partially occupies its own morphospace while also crossing into the morphospace of Astarte undulata and Astarte symmetrica. Astarte undulata shows the second highest morphological variability but does not cross into the morphospace of Astarte symmetrica showing that those two proposed species are likely valid.

If this pattern is robust to the addition of more individuals and species, the resulting data can be used to pinpoint morphological differences between species and aid in identification of the species studied. If this pattern does not hold, the data collected can be used to suggest which species within the genus should be synonymized.