1. Trivia arctica withdrawing into shell. The animal can completely withdraw into the slit aperture of the shell. It lacks an operculum to block the opening, relying on its constriction to exclude attackers.
2. Trivia arctica withdrawing into shell. The animal can completely withdraw into the slit aperture of the shell. It lacks an operculum to block the opening, relying on its constriction to exclude attackers.

Trivia arctica withdrawing into shell. The animal can completely withdraw into the slit aperture of the shell. It lacks an operculum to block the opening, relying on its constriction to exclude attackers.