Gastropods · Systellommatophora · Onchidiidae

Warty Slug

Onchidium verruculatum

Not Evaluated

It has not yet been assessed against the IUCN criteria. See full glossary

A pulmonate sea slug without a shell, its back warty and looking like a wet stone. It breathes air through a lung and comes out to feed as the tide retreats, rasping the microalgal biofilm from the rocks with its radula. When the tide comes back in it always returns to the same crevice.

Size

3 cm – 7 cm

Diet

Herbivore

Feeds mainly on plants.

Social structure

Colony

Lives in large concentrations, often for breeding reasons.

Sighting difficulty

Unknown

OceanHerbivore Colonial Ocean Mollusc

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Fun facts

As well as the eyes on its head, it has accessory eyes on the papillae of its back, complete with retina and lens, which let it detect the shadows of predators from above.
It is not a nudibranch despite its looks: it is a pulmonate, more closely related to land slugs than to sea slugs. It breathes air with a lung.
Its eyes sit at the tips of two head tentacles, and it also has dorsal eyes scattered over its back, which is most unusual.
It always returns to the same refuge. It comes out to feed at low tide and finds its way back along its own mucus trail; a 1981 study showed that the outward and return trails carry different information.
When submerged it unfurls branched gill papillae from its tubercles that look like a nudibranch's gills, and only on picking it up does its pulmonate anatomy become obvious.