Ammonicera is a genus of minute sea snails, marine gastropod molluscs or micromollusks in the family Omalogyridae. They are found in various locations such as the Eastern Pacific coasts of the United States and Mexico, Japan, and the Mediterranean.

This genus comprises the smallest gastropods known, featuring discoid, planispiral shells that typically measure in the adult state 1 mm or even less in size. The protoconch is characterized by distinct ridges and grooves. The teleoconch typically displays prominent sculpture, though it is occasionally weak. The aperture ranges from rounded to subquadrate.

The diet of the Ammonicera is not confirmed, however, based on the diets of other Omalogyridae, it is assumed to feed on several algal species in its habitat.

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