Wikipedia
A micromollusk is a shelled mollusk which is extremely small, even at full adult size. The word is usually, but not exclusively, applied to marine mollusks, although in addition, numerous species of land snails and freshwater mollusks also reach adult size at very small dimensions.
These tiny mollusks or their tiny shells are easy to overlook, as many of them are not very noticeable to the naked eye, and thus many people are not aware that they even exist. Nonetheless there are large numbers of families and vast numbers of mollusk species, in particular marine gastropods or sea snails, which are minute enough to be considered micromollusks.
Considerable numbers of marine gastropod species are only about 5 or 6 mm in adult size; many others are only about 2 or 3 mm in adult size; and a few have adult shells which are as small as one millimeter or even smaller still. Despite their tiny size, many of the shells have a good deal of elaborate sculpture. A fair number of them are even quite colorful, although many others are colorless and translucent.
Certain species of micromollusks are very common in the right habitat, and can on occasion be present in huge numbers. However, because of their minute size, micromollusks often go unnoticed by beachcombers, shell collectors and even more serious conchologists.
Micromollusks are not very popular as a subject of study, even among professional malacologists, primarily because these minute species can be very challenging to work with. It can often require great care, patience and persistence to find micromollusks, sort them, store them, and identify them correctly. Working with them usually also requires special techniques and special equipment compared with that needed for most of the larger shelled species. Discriminating the features necessary for successful identification of micromollusks to the species level almost always requires a stereo or dissecting microscope. Identifying, or adequately photographing, the smallest species may sometimes require a scanning electron microscope. Access to a first rate scientific research library is also often necessary, since many of the popular shell identification books and field guides either omit micromollusks completely, or only include a very few species for any particular area.
Because of all these various challenges, micromollusks are poorly known compared to their larger relatives, and thus there are undoubtedly numerous species which have yet to be discovered and described. holotype), Truncatella bilabiata bilabiata, Truncatella pulchella.