I Present to you the Nudibranch...

Living Color

Toxic nudibranchs—soft, seagoing slugs—produce a brilliant defense

By Jennifer S. Holland

National Geographic Staff

Photograph by David Doubilet

Nudibranchs crawl through life as slick and naked as a newborn. Snail kin whose ancestors shrugged off the shell millions of years ago, they are just skin, muscle, and organs sliding on trails of slime across ocean floors and coral heads the world over.

Found from sandy shallows and reefs to the murky seabed nearly a mile down, nudibranchs thrive in waters both warm and cold and even around billowing deep-sea vents. Members of the gastropod class, and more broadly the mollusks, the mostly finger-size morsels live fully exposed, their gills forming tufts on their backs. (Nudibranch means "naked gill," a feature that separates them from other sea slugs.) Although they can release their muscular foothold to tumble in a current—a few can even swim freely—they are rarely in a hurry.

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