The Surprisingly Bold and Beautiful World of Sea Slugs

On land, slugs are far from nature's most beautiful creatures—but underwater, the family of shell-less creatures known as nudibranchs come in bright neons, glowing pastels, and vibrant primary colors. The 3,000 different kinds of nudibranchs get their color from the food they eat—and, in some cases, secrete the poisons from their prey to defend themselves against predators.

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Fried Egg Nudibranch

credit: Migrated Image

The Fried Egg Nudibranch gets its name from the perfect yellow-and-white circles that line its back. These nudibranchs grow to about three inches long, and live in the waters of the Pacific and the Red Sea. Click through for more brilliant 'branches in a rainbow of colors. Photo via Jon Hanson @ flickr

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Nembrotha Kubaryana

credit: Migrated Image

You'll recognize this nudibranch by its distinctive black, green, and orange coloring; look for them in Indonesia, Malaysia, the Philippines, and Australia. While nudibranchs are in danger from the same threats that face other marine life -- like plastic and other pollution and coastal development --their population status is harder to figure out: scientists don't have a good idea of how many exist, total, so it's tricky to determine their decline. Photo via Prilfish @ flickr

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Chromodoris Elizabethina

credit: Migrated Image

Also known as the Twisted Nudibranch, the Chromodoris family is known for its yellow edging, though the other colors can range from turquoise and white to red and black. Photo by Cybersam @ flickr

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Notodoris Minor

credit: Migrated Image

These neon slugs make their homes on reefs in the Indo-West Pacific waters, where they eat chalky sponges that contain calcium carbonate, nourishment that helps them grow as long as 5 inches. Photo via Prilfish @ flickr

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Dendronotus Irus

credit: Migrated Image

"Giant" is a relative term when it comes to nudibranchs, but these Pacific coast-dwelling slugs earned it for their potential to measure as much as a foot long. Photo via Dan Hershman @ flickr

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Glaucus Atlanticus

credit: Migrated Image

The brilliant blues of this nudibranch--which lives on top of the water rather than under the sea--camouflage it from airborne predators; underneath, they're a pale gray to slip past underwater enemies. Photo via Neatorama

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Tritoniopsis Elegans

credit: Migrated Image

Found in waters all over the world, the Tritonopsis Elegans shows up in orange, white, and reddish tones--though the variety in this case doesn't seem to be dependent on food, since different organisms on the same coral have been found in different colors. Photo via threefingeredlord @ flickr

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Dirona Albolineata

credit: Migrated Image

This glowing frosted nudibranch looks gentle, but it's outfitted with a strong mouth that lets it feed on snails--so it thrives on docks, pilings, and shoreside rocks where food is plentiful. Photo via Dan Hershman @ flickr

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Triopha Catalinea

credit: Migrated Image

The white body and circus-orange spots gave this slug its nickname: clown nudibranch. They're still easy to miss, though, since most are less than three inches long. Photo via Ed Bierman @ flickr

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Pectenodoris Trilineata

credit: Migrated Image

The tiniest nudibranch on this list, the bluish-purple Pectenodoris Trilineata often stops growing at just 7 millimeters; look for them on similarly-colored coral in the western Pacific ocean. Photo via Stephen Childs @ flickr