The fat Guam partula or humped tree snail, scientific name Partula gibba, is an endangered species of air-breathing land snail, a terrestrial gastropod mollusk in the family Partulidae.

This species occurs throughout the Mariana Archipelago, and has been reported in the greatest densities and population sizes on the isle of Sarigan.

[4] On Sarigan, the species has been recorded most frequently in high-elevation native forests on the trunks of large Erythrina variegata specimens, often resting at the base of branches.

On 19 May 2015 specimens were found consuming the Pandanus-fruit ejecta of the Mariana fruit bat on the leaves of a Pandanus tectorius tree.

Mariana partulids have been noted to consume plant material, both living and decaying.