Abstract
The anatomy of the marine pulmonate slug Onchidium vaigiense Quoy and Gaimard, 1824, originally described from West Papua, Indonesia, is re-described here based on 44 specimens from 15 localities from the Philippines, Papua New Guinea, Indonesia and Singapore, many of which are new distribution records. Onchidium marmoratum Lesson, 1826, and Onchidium leopoldi Labbé, 1934, are regarded as new synonyms of Onchidium vaigiense. The anatomy of Onchidium vaigiense is compared with that of other species; its supra-specific relationships are discussed; and some important features in onchidiid systematics are discussed.