Cystiscus vavauensis is a species of very small sea snail, a marine gastropod mollusk or micromollusk in the family Cystiscidae.

The following is from the Wikipedia page for the genus Cystiscus: Shell minute to small (adult length 1 to 6 mm (0.039 to 0.236 in)).

Color white, hyaline; surface smooth, glossy.

Shape usually elliptic, obovate, or subtriangular; weakly shouldered.

Lip slightly to distinctly thickened, flared posteriorly in some species, smooth on inside edge to weakly denticulate, lacking lirae, external varix absent.