Marine Pulmonate slugs

Order: Systellommatophora
Family: Onchidiidae


Worldwide, intertidal.


Onchidium damelii, a common onchidiid in mangrove swamps in New South Wales, Australia, where it is found in large numbers on the mudflats. Length 35mm.
PHOTO: Stephanie A. Clark.

The onchidioideans are shell-less slug-like marine molluscs. They range in size from 10-70mm long. They are usually oval in shape with a hard leathery mantle which ranges from smooth in some species to tuberculate in others. Some species have gill-like papillae scattered over the back and in other species there are eye-like sensory structures on the back. These relatives of the land snails have a section of the mantle cavity modified as a lung to breath air. It opens through a pore alongside the posteriorly opening anus, below the mantle.

Onchidiids live intertidally, often in sheltered estuaries on rocks, mud, and in mangrove swamps. They are also found on limestone cliffs with wide raised intertidal limestone platforms. Little has been published on their natural history but it is thought they feed on the organic film of diatoms, other algae, and bacteria which coat rocks and mud on sheltered intertidal shores. Genera include Onchidium, Onchidella, Onchidina and Platevindex.

Authorship details
Rudman, W.B., 1999 (January 13) Marine Pulmonate slugs. [In] Sea Slug Forum. Australian Museum, Sydney. Available from

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