micromollusk

Micromollusk is a descriptive term used for mollusks whose shells or bodies are very small, typically less than 5 millimeters in maximum dimension. It is not a formal taxonomic group; rather it groups numerous tiny gastropods and bivalves, many of which remain poorly known due to their size. Some authors apply a stricter threshold (1–2 mm) for certain subgroups, which can lead to variation in what is counted as a micromollusk.

Micromollusks occur in a wide range of environments, including marine, freshwater, and terrestrial habitats, across most geographic regions. They are especially common in microhabitats such as leaf litter, mosses, sediment grains, coral rubble, and shallow aquatic zones. Their small size makes them easy to overlook, but they can be highly diverse and abundant in suitable microhabitats.

Studying micromollusks requires specialized collection and identification methods. Researchers typically use fine sieves and sediment or litter decanting to separate microfauna, followed by examination under a dissecting or compound microscope. Identification relies on shell morphology, and for many groups, features of the soft body or radula. Increasingly, molecular techniques such as DNA barcoding, and imaging methods like scanning electron microscopy, aid in distinguishing closely related species.

Ecology and life history vary among micromollusks, but most are detritivores, microalgae grazers, or filter feeders. They can be hermaphroditic, with diverse reproductive strategies and developmental modes. Because of their abundance and sensitivity to environmental change, micromollusks are used in biodiversity assessments, ecological surveys, and paleontological studies as indicators of habitat quality and historical conditions.