Morphological analysis
To confirm the molecular results (i.e., the presence of two distinct lineages detected from the molecular analysis), we examined shell morphometrics of M. virgata populations. A total of 15 shell characters (supplementary Fig. 1) were measured from 50 randomly selected individuals from each lineage (100 individuals in total). Measured shell characters were log-transformed, and principal components analysis (PCA) was performed in R-studio to assess morphological differences between the two lineages.