Paromoionchis tumidus is a species of small, air-breathing sea slug, a shell-less marine pulmonate gastropod mollusc in the family Onchidiidae.
Paromoionchis tumidus is widely distributed in the Indo-Pacific from Japan in the north, to Hong Kong, Vietnam, the Philippines, Brunei Darussalam, Singapore, Peninsular Malaysia, the Andaman Islands, Indonesia, and Australia (New South Wales, Northern Territory, Queensland).
The following names have been synonymized with Paromoionchis tumidus: