A MORPHOLOGICAL COMPARISON OF RECENT AND PLEISTOCENE PHRONTIS VIBEX (MOLLUSCA: GASTROPODA: NASSARIIDAE) FROM SOUTHWESTERN FLORIDA

Phrontis vibex is a species of snail in the family Nassariidae. Nassariids (Nassa mud snails) are marine grazing organisms which are found in intertidal habitats. Extant Phrontis vibex populations are widely distributed along the Atlantic coast, in the Gulf of Mexico, and throughout the Caribbean. They are also abundant in the Quaternary fossil record. For this study, we compared body size and morphological traits of fossil and Recent Phrontis vibex to identify patterns in their shell size and shape over time. The Recent Phrontis vibex specimens (n=120) are from six separate localities and the fossil specimens (n=80) are from two localities of the lower Pleistocene Caloosahatchee Formation and two localities of the upper Pleistocene Fort Thompson Formation (all from southwestern Florida). The Recent and fossil specimens are respectively reposited at the Invertebrate Zoology Division and the Invertebrate Paleontology Division at the Florida Museum of Natural History.

Specimens used for this pilot study were photographed and the linear variables (total length, body whorl length and width, aperture length and width, penultimate whorl length and width, width of the parietal shield, thickness of outer lip, angle of spire, and length of the spire) were extracted from the photographs using the software ImageJ. A Principal Component Analysis (PCA) using eleven linear measurements was conducted. The Recent and fossil specimens do not form distinct groups in the PCA ordination plots and the morphological variability is comparably high for both Recent and fossil specimens. These are preliminary results and future landmark based Geometric Morphometric Analyses, based on an expanded specimen-level dataset should help us to assess preliminary patterns of body size and shape in fossil and Recent Phrontis vibex specimens.