The red triangle slug, Triboniophorus graeffei, is a species of air-breathing land slug, a terrestrial pulmonate gastropod molluscs in the family Athoracophoridae, the leaf-veined slugs. Native to eastern Australia, this species is named after the distinctive red triangle marking on its back. Reaching lengths of up to 15 centimeters (about 6 inches), it is not only striking in appearance but also holds the title of Australia's largest native land slug. It’s a familiar and widespread presence in its natural habitat.

Triboniophorus graeffei is the type species of its genus, Triboniophorus, the key representative of the group. A closely related and visually unique species of Triboniophorus has been identified from Mount Kaputar, though it has yet to be formally described.

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