Sea Slugs
En Español
Dive into the underwater world of nudibranchs. Learn how they turn the food they eat into color, energy, and even weapons.
You are what you eat. Have you heard that before? Food gives you energy. Well, for sea creatures called nudibranchs, food is more than just energy. Food makes them colorful. Sometimes it protects them from enemies. Of course, nudibranchs are very choosy eaters. And it's no wonder. Their food holds the secrets to their survival.
Out of Their Shell
Before we get to the food facts, you should know a bit about nudibranchs. They are a type of sea slug. Sea slugs are mollusks. Clams, oysters, and snails are mollusks, too. All those animals have shells for protection.
Nudibranchs don't. They are just blobs of muscle, skin, and organs. They breathe through gills. The gills stick out of their backs like feathers!
Slugs On the Move
Most nudibranchs are about the size of your finger. They live in both cold and warm waters. Some even live near hot underwater volcanoes!
Nudibranchs are slow. They use a muscle called a sticky foot to crawl along the seafloor. Some can swim. The Spanish dancer squeezes and releases its muscles to swim. It looks like a dancer's swishing skirt!
Living Color
Some nudibranchs are as colorful as a candy store. One type has pink dots and red gills. Another is blue with yellow and black stripes. Some are round. Others are long.
Now you're ready for the first food fact. Nudibranchs get their colors from their food! Nudibranchs dine on anemones, corals, and sponges.
When a slug eats a red sponge, it turns red. Matching the color of its food helps a nudibranch survive. A predator may not see a red slug eating a red sponge. Nudibranchs cannot see their own colors. They see only white, black, and gray.
A nudibranch doesn't have a nose, ears, or tongue. Instead, it has rhinophores. Sea slugs use them to smell, feel, and taste.
Snack Attack!
Ready for food fact number two? Nudibranchs can turn their food into weapons! Some eat stinging anemones. The stingers settle in the cerata. Those are parts some nudibranchs have for breathing and digestion. If attacked, the sea slugs can use the stingers as weapons!
That's not all. Some nudibranchs eat toxic sponges. The slugs save the poisons in their bodies. Then when an enemy is near, they let out a cloud of the poison. Spanish dancers even put the poison in their eggs. This protects their eggs until they hatch.
Some nudibranchs can't store poison. So they mimic ones that do! Predators can't tell the two species apart. So they leave them both alone.
Solar Power
Many nudibranchs eat only one kind of coral or anemone. It can be hard for them to find food. They might have to wait a long time between meals. No problem! Here's the last food fact. Some sea slugs make food inside their bodies. Here's how.
The blue dragon eats coral filled with tiny plants called algae. The slug saves the algae in its cerata. This is the secret to its survival.
Algae, like other plants, use sunlight to make food. This is called photosynthesis. Inside the slug's body, the algae keep using sunlight to make food. That food gives the nudibranch energy. Now it can go for days without eating!
Slug Studies
Scientists think nudibranchs are important to study. They want to know how nudibranchs are able to learn and remember things. This could help teach scientists more about how the human brain works.
The chemicals the slugs use may be important, too. They might help heal human organs. Imagine! Not bad for a little blob at the bottom of the ocean.
Article by Rebecca Paley. Top-of-page photograph © Borut Furlan/Peter Arnold Inc. "Sea Slugs" appears on page 2 of the Nov.-Dec. 2009 issue.
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