Micromollusks, by definition, never grow larger than 5 mm (0.2 inches). Despite their small size, micromollusks may have shells as attractive as those of their larger-sized cousins, and have life processes just as complex. Scientific surveys done in different regions of the planet indicate that very large shares of the marine mollusk biodiversity in those areas consist of micromollusks.
For instance, on Sanibel and Captiva islands (Florida) alone, there are at least 20 species of vitrinellas (photo) in the closely related families Tornidae and Teinostomatidae. To learn more about “micros,” register for my upcoming (May 17) talk “Micromollusks-The Allure of Small Size” at the National Shell Museum web site.