The coffee bean snail (Melampus bidentatus) is a common detritivore in salt marshes on the US Atlantic coast. Using single gene sequencing, three cryptic species have been identified within M. bidentatus. Despite their high potential for dispersal as larvae, the three species have very different range extents, especially their northern limits. We are exploring physiological differences that may help explain this. Surprisingly, we have found that all three species have similar abilities to survive freezing conditions. We are now using tests of multiple stressors to examine the relationship between freeze tolerance and oceanic salinity. At the same time, we are using whole genome sequencing to more fully understand the relationship among cryptic species. Interestingly, karyotyping work from half a century ago suggests that chromosomal differences could exist between taxa.