this family exhibits a great diversity in shell morphology but extremely homogeneous anatomical traits. diversity of shell morphology is linked to substantial eco-phenotypic plasticity. hubendick (1951) illustrated this point by compiling up to 1143 species names, a large number of which he synonymized. in contrast, the anatomy of their reproductive tracts (including prostate, penis and preputium) is extremely homogeneous. immunological, cytogenetical, enzyme electrophoresis studies, and dna-based approaches have demonstrated extensive homoplasy in anatomical characters.