Aplustrum amplustre, also known as royal paper bubble, ship’s flag shell, swollen bubble, is a species of sea snails, bubble snails, marine opisthobranch gastropod mollusks in the family Aplustridae.

shell with horizontal lines, with lightbrown stripes, outlined in black, alternating with translucent white and pink stripes patterns; the animal is too large to fit inside its shell.

Empty shells are used by hermit crabs.

The species is distributed in warm sea[6]: 83 [2] around tropical Indo-Pacific: Australia, New Zealand, South of Kyūshū of Japan,[6]: 83  South Africa to Hawaii, Madagascar, Philippines.

It lives in shallow water (10 metres below sea level) on reefs, with a mix of fine sand, rock and turf algae.