Everything Nudibranch

Want to learn more about nudibranchs? You’ve come to the right place! Scroll to learn more about these fascinating sea creatures.

What are nudibranchs?

Nudibranchs (pronounced new-de-brawks) are a type of sea slug. Nudibranchs are classified as soft-bodied marine gastropod mollusks. Technically, all nudibranchs are sea slugs, but not all sea slugs are nudibranchs. Confused yet? Let’s break it down.

All animals in the world are part of the animal kingdom - this includes everything from bugs to fish to birds to mammals. Animals are then organized into smaller and more specific groups using a system of taxonomy. Here’s what the nudibranch taxonomy looks like:

Two types of nudibranchs

Mollusks: Mollusks are soft-bodied invertebrate animals with shells. But wait, you say, nudibranchs don’t have shells! And that’s mostly true. Nudibranchs shed their shells after the larval stage - so teeny, tiny baby nudibranchs had shells at one point, but as adult animals, they don’t need their shells any longer because they have other, better defense mechanisms (more on that in a minute). Other mollusks include octopuses, snails, oysters, clams, cuttlefish, and periwinkles.

Gastropods: Gastropods are slugs and snails. They can live in freshwater, saltwater, or on land. All gastropods have a muscular foot they use to propel them on land or through water, and most have sense organs on the head that help the animal find prey and escape predators. Many gastropods have shells and many do not. Some gastropods you might be familiar with include banana slugs, abalone, and whelks.

Nudibranchs: Nudibranchs are a type of sea slug. Just like land slugs, they slide along the ground, but nudibranchs do so underwater. The word “nudibranch” means naked gills. This is in reference to the appendages that protrude from their backs. On dorid nudibranchs, these appendages look like rosette plumes on the nudibranch’s rear end, and on aeolid nudibranchs, they look like dozens of spikes running along the nudibranch’s back. These appendages are the nudibranch’s gills.

Not nudibranchs but close: Nudibranchs are related to other sea slugs like sea hares, sap-sucking slugs like the leaf sheep, and bubble snails. While they may not be nudibranchs, we love them anyway!

There are two main types of nudibranchs: Dorid nudibranchs and aeolid nudibranchs. These terms refer to what the nudibranch body shape looks like.

Dorid Nudibranchs

Dorid nudibranchs look fairly smooth, like typical land slugs. There is a tuft of feathery appendages toward the back of these nudibranchs that serve as gills.

Nudibranch Anatomy

• Rhinophores: The word rhinophore comes from the Greek root rhino, which means “nose.” Rhinophores are scent receptors that sense chemical molecules dissolved in the water. Rhinophores help nudibranchs find their food. Because rhinophores are vulnerable to environmental dangers, many species of nudibranch are able to retract the rhinophores into a pocket beneath the skin.

• Gill Plume: The flower-like plume on the back of dorid nudibranchs is used for respiration. These are the “naked gills” for which nudibranchs are named.

• Cerata: In aeolid nudibranchs, cerata are the nudibranch’s respiratory organ much like the gill plume is in dorid nudibranchs. In some species, cerata are used for attack and defense.

• Foot: The flat, broad muscle at the bottom of the nudibranch is how a nudibranch propels itself across the ground. Some nudibranchs can short distances by flexing the foot muscle.

• Eye Spots: Nudibranchs do have eyes, but scientists believe these rudimentary organs can only discern the difference between light and dark.

• Mantle: In dorid nudibranchs, the mantle extends over the foot, offering some protection to the creatures.

• Oral Tentacles: The oral tentacles are used for identifying food by touch and taste.

Blue Dragon (Glaucus atlanticus)

Size: Up to 3 centimeters long

Diet: Portuguese man o’ war and blue button jellyfish

Habitat: Atlantic, Pacific, and Indian Oceans

Interesting facts: The blue dragon lives its entire life floating on the open ocean. It often floats upside, showing its bright blue markings to airborne predators.

Nudibranch Facts

• There are over 3,000 species of nudibranchs. They are found all over the world.

• Nudibranchs vary widely in size from a quarter of an inch long to 12 inches long.

• Nudibranchs are fierce predators, and individual species have very specific food preferences. Generally, nudibranchs eat sponges, coral, anemones, hydras, jellyfish, bryozoans, and ascidians.

• Nudibranchs have something called a radula inside their mouths, which is a ribbon-like structure made of teeth.

• Nudibranchs can steal stinging cells from their prey and store toxins inside their cerata for later use against threats.

• Nudibranchs get their color from the food they eat, which aids in camouflage.

• Some nudibranchs glow in the dark using a process called bioluminescence.

• Some nudibranchs emit pleasant smells! The Melibe leonina smells like watermelon, the Acanthodoris lutea smells like cedar, and the Peltodoris nobilis smells like citrus.

• Nudibranchs are hermaphrodites. After mating, both parents will lay eggs. Eggs are laid in ribbon shapes.

• Some nudibranchs don’t even have to eat - these nudibranchs store photosynthetic algae in their cerata. The algae then converts light into energy for the nudibranchs.

• The nudibranch life span is short - between a few weeks and up to a year.

Meet the Ebb Tide Toys Nudibranchs