Nudibranchs are shell-less marine molluscs that weaponize their prey to survive in the wild.

Nature · Published 29 September 2026 Swipe more like this →

In short: These soft-bodied creatures shed their shells after the larval stage, evolving into masters of chemical warfare and camouflage. From the intertidal zone to the deep ocean, they use stolen stinging cells and toxic metabolites to deter predators, proving that being naked in the sea is a surprisingly effective strategy.

Nudibranchs, a group of about 3,000 known species, are marine gastropod molluscs that undergo a dramatic transformation. While most begin life as swimming veliger larvae with coiled shells, they shed these protective coverings during metamorphosis. As adults, they are typically benthic, crawling across the substrate, though a few species like the neustonic Glaucus nudibranchs float upside down at the surface, and the recently described Bathydevius exhibits a unique bathypelagic lifestyle at depths near 2,500 meters.

Their survival strategies are remarkably diverse. Many species are carnivores that feed on sponges, hydroids, or anemones. Some, such as those feeding on hydrozoids, perform a feat of biological theft by sequestering their prey's stinging cells, or nematocysts, within their own dorsal appendages known as cerata. These kleptocnidae are transported through the gut to the hind body, where they are deployed as a defensive weapon. Other nudibranchs concentrate chemical defences from their diet, rendering themselves distasteful to potential predators, while some species can even synthesize their own chemical compounds de novo.

Taxonomy remains a field of active revision. Traditionally grouped within the now-invalidated Opisthobranchia, nudibranchs are currently understood as part of the Nudipleura clade. Recent research, including a 2025 study by Korshunova and colleagues, has proposed further restructuring, suggesting the separation of dorid nudibranchs—recognized by their rosette of naked gills—into their own order. This ongoing debate highlights the complexity of these organisms, which range in size from 4 to 600 millimeters and continue to surprise scientists with behaviors like bioluminescence and even reports of audible communication.

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