Thylacodes sipho, the common worm-shell, is a species of sea snail, a worm shell, a marine gastropod mollusc in the family Vermetidae, the worm snails.

Endemic to Australia, found in all coastal states, more common in the south.

The habitat is subtidal exposed reefs and rock platforms.

The early whorls of the shell are attached to a substrate such as rocks or shells, sometimes in aggregated groups.

Feeding is on organic matter, trapped in strings of mucous, there is no operculum.