Species identification and delineation
Our operational criterion for the delimitation of species has been to test whether candidate species were phenotypically and genotypically distinct from each other (Sites and Marshall, 2004). Specimens have initially been grouped into morphospecies based on external morphology, including shell characters. These groups have been associated with already described species with respect to morphological similarity and distribution as based on comparison with types and/or topotypes. Morphospecies that could not be assigned to an available species name were treated as candidates for new species. Subsequently, we employed basic statistics of morphometric characters and comparative reproductive anatomy to assess the amounts of phenotypic differentiation within and between the so recognized morphospecies. In a final step we employed analyses of DNA sequences to assess the amount of mitochondrial differentiation within and between morphospecies.