Nudibranch

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The bottom-dwelling, jelly-bodied nudibranch (NEW-dih-bronk) might seem an unlikely canvas for Mother Nature to express her wildest indulgences of color and form. 

But these shell-less mollusks, part of the sea slug family, bear some of the most fascinating shapes, sumptuous hues, and intricate patterns of any animal on Earth.

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Nudibranch - Stiliger  Photo by Pipat Kosumlaksamee
Donut nudi by Pipat Cat Kosumlaksamee

There are more than 3,000 known species of nudibranch, and new ones are being identified almost daily. They are found throughout the world’s oceans, but are most abundant in shallow, tropical waters.

Their scientific name, Nudibranchia, means naked gills, and describes the feathery gills and horns that most wear on their backs. Generally oblong in shape, nudibranchs can be thick or flattened, long or short, ornately colored or drab to match their surroundings. They can grow as small as 0.25 inches (6 millimeters) or as large as 12 inches (31 centimeters) long.

nudi by Pipat Cat Kosumlaksamee
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Nudi

They are carnivores that slowly ply their range grazing on algae, sponges, anemones, corals, barnacles, and even other nudibranchs. To identify prey, they have two highly sensitive tentacles, called rhinophores, located on top of their heads. Nudibranchs derive their coloring from the food they eat, which helps in camouflage, and some even retain the foul-tasting poisons of their prey and secrete them as a defense against predators.

Nudibranchs are simultaneous hermaphrodites, and can mate with any other mature member of their species. Their lifespan varies widely, with some living less than a month, and others living up to one year.

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Nudi and shrimp
Nudibranchs

Nudibranchs possess both female and male reproductive organs, but they don’t often self-fertilize. Having both sexual organs means that there is always a chance for reproduction if two adults of the same species cross paths. This is smart, considering their solitary, wandering lifestyles. Egg masses are generally laid on whatever surface the animal is feeding on (as on hydroids in the picture below) and are usually spiral shaped or coiled. The eggs develop into planktonic (free swimming) larvae, which drift on ocean currents until they settle out as adults. Nudibranchs are gastropod mollusks.

They belong to the same phylum that includes the whelks and many other shells that you find along the beach. Nudibranchs have just evolved a different type of body for a very different lifestyle – one that doesn’t require them to surround themselves with a protective shell.

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Their body is soft and fleshy, they move around on a long muscular foot (similarly to land snails) and they have specializedtentacles (rhinophores) on their head that scientists believe they use to touch and sense their immediate environment.

Some nudibranchs have a bushy cluster of gills toward the back of their body that they use for respiration, while others have tentacle-like structures (cerata) all over their body that are used for both respiration and defense.

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August 25, 2016 |

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