Animated coloured scanning electron micrograph (SEM) of Mediterranean mollusk (gastropod) shell (Danilia octaviana). This gastropod shell is considered a microshell with very ornate structure. A micromollusc is a shelled mollusk (also called a micro shell) which is very small, even at full adult size. It is hard to discern them with the naked eye. Marine micromolluscs (marine gastropods) have a large number of families and species.