DISTINGUISHING BETWEEN CLOSELY RELATED SPECIES WITHIN A LINEAGE: GEOMETRIC MORPHOMETRICS OF MULINIA OF THE ATLANTIC COASTAL PLAIN, U.S.A
Preliminary analysis of 388 valves reveals that differences between the two Mulinia species are significant enough to distinguish them from one another based on 15 geometric landmarks using the Procrustes method. Discriminant analysis yielded classificatory errors rates of 3% when individual specimens were reclassified into a priori groups based on average shape values of each species. Using M. congesta as a reference, thin-plate spline analysis suggests the umbo of M. lateralis moved towards the anterior of the valve, the pallial sinus is closer to the posterior of the valve and both muscle scars moved into the interior of the valve slightly. In addition to these allometry-free shape differences, the two species differ in terms of size (á=0.05, p <0.0001, Wilcoxon), with M. congesta having greater size variability and overall size than M. lateralis . These results imply that quantitative traits can be used successfully to distinguish Mulinia species, and support the taxonomic validity of the two species.