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Nudibranchs General

Mollusca Gastropoda

Nudibranchs are colorful, soft-bodied marine snails that lack a hard shell. They are commonly known as sea slugs. They are members of the class gastropoda (snails and slugs) and move around on a large muscular foot which often leaves a slime trail. There are about 3000 known species.

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SPECIES IN DETAIL

Nudibranchs General

Mollusca Gastropoda

CONSERVATION STATUS: Not evaluated

CLIMATE CHANGE:

Geographic Distribution

Sea slugs can be found throughout the world occupying a wide range of environments. They prefer warm tropical reefs but can be found in temperate waters as well. A few species are able to survive in extreme areas such as the Antarctic waters and deep sea hydrothermal vents.

Habitat

Nudibranchs live in a wide range of habitats including shallow tide pools, coral reefs, and sandy bottoms to the oceans’ depths at or over 2000 meters (6,561 feet). All nudibranchs are benthic animals meaning they crawl along on the ocean bottom.

Physical Characteristics

Rhinophores, a pair of tentacles, are found on the head of nudibranchs. The tentacles are used to taste, touch and smell. A tiny pair of eyes is located near the base of the rhinophores. The name nudibranch in Latin means “naked gill” and several gills may be seen along the back and rear of the animal that stick out from the body. The gills absorb oxygen out of the water.

Size

The smallest nudibranchs are microscopic or just a few millimeters long while the largest animals can grow to half of 1 meter (18—19 inches). The heaviest nudibranchs can weigh up to 1.5 kilograms (3 pounds).

Diet

Nudibranchs are carnivorous and feed on sea anemones, sponges, soft corals, tunicates, and other invertebrates. Many nudibranchs use a toothed scraping structure called a radula to help them feed. The radula is tough enough to scrape materials off hard surfaces or tear off small pieces of their prey. A few types will inject their prey with chemicals which begin digesting the body and then they suck out the liquified tissues. Still others will use symbiotic zooxanthellae algae like many corals to convert sunlight into food.

Reproduction

Nudibranchs are hermaphroditic which means they have both male and female reproductive organs. As slow moving solitary animals, nudibranchs benefit from their hermaphroditism as they can mate with any adult they encounter. After mating, nudibranchs lay masses of coiled (spiral shaped) eggs. The eggs hatch into larvae which settle to the ocean bottom. Most nudibranchs do not care for either the eggs or young.

Behavior

Nudibranchs play an important part in the food web both as predators of soft corals, sea anemones, tunicates, and sponges and as prey of other nudibranchs, sea slugs, crabs, lobsters, turtles and humans. Nudibranchs spend much of their day grazing or prowling for food.

Adaptation

An animal with a soft body makes a tempting target for predators. To protect themselves, nudibranchs employ a number of adaptations. Some nudibranchs blend in with their environment using camouflage or mimicry. Predators have a hard time seeing a nudibranch when it blends in with the sponge or coral it is crawling upon. Other nudibranchs are brightly colored to warn potential predators that they are distasteful or toxic. Nudibranchs can give off offensive tastes and odors depending on what they have been feeding on. Once predators have had a bad experience with a nudibranch they tend to avoid a second encounter. A few nudibranchs can feed on animals with stinging cells like corals and jellies. The stinging cells can move into the cells of the nudibranch without being digested and pass on their ability to sting.

Longevity

The average lifespan of nudibranchs is about one year.

Conservation

Conservation efforts should create, maintain, and manage marine protected areas to prevent habitat destruction—particularly at reefs. The establishment of support programs that mitigate the effects of global warming which affects the range of nudibranchs should be prioritized. Protective limits need to be managed to restrict overfishing of nudibranch species for the aquarium trade.

Special Notes

The Spanish dancer is a large bright red nudibranch which has the ability to swim from one location to another by flexing its entire body back and forth. The movement resembles the back and forth movement of the skirt of a Spanish flamenco dancer.

The blue glaucus (blue dragon), unlike most nudibranchs that crawl along the bottom, floats near the surface of the ocean. At the surface it feeds on the stinging cells of the Portuguese man o’ war. These stinging cells can move through the body of the animal without being digested. The cells settle in the tissues of the animal and if touched can give a powerful and painful sting as if you touched the Portuguese man o’ war itself.

SPECIES IN DETAIL | Print full entry

Nudibranchs General

Mollusca Gastropoda

CONSERVATION STATUS: Not evaluated

CLIMATE CHANGE:

Sea slugs can be found throughout the world occupying a wide range of environments. They prefer warm tropical reefs but can be found in temperate waters as well. A few species are able to survive in extreme areas such as the Antarctic waters and deep sea hydrothermal vents.

Nudibranchs live in a wide range of habitats including shallow tide pools, coral reefs, and sandy bottoms to the oceans’ depths at or over 2000 meters (6,561 feet). All nudibranchs are benthic animals meaning they crawl along on the ocean bottom.

Rhinophores, a pair of tentacles, are found on the head of nudibranchs. The tentacles are used to taste, touch and smell. A tiny pair of eyes is located near the base of the rhinophores. The name nudibranch in Latin means “naked gill” and several gills may be seen along the back and rear of the animal that stick out from the body. The gills absorb oxygen out of the water.

The smallest nudibranchs are microscopic or just a few millimeters long while the largest animals can grow to half of 1 meter (18—19 inches). The heaviest nudibranchs can weigh up to 1.5 kilograms (3 pounds).

Nudibranchs are carnivorous and feed on sea anemones, sponges, soft corals, tunicates, and other invertebrates. Many nudibranchs use a toothed scraping structure called a radula to help them feed. The radula is tough enough to scrape materials off hard surfaces or tear off small pieces of their prey. A few types will inject their prey with chemicals which begin digesting the body and then they suck out the liquified tissues. Still others will use symbiotic zooxanthellae algae like many corals to convert sunlight into food.

Nudibranchs are hermaphroditic which means they have both male and female reproductive organs. As slow moving solitary animals, nudibranchs benefit from their hermaphroditism as they can mate with any adult they encounter. After mating, nudibranchs lay masses of coiled (spiral shaped) eggs. The eggs hatch into larvae which settle to the ocean bottom. Most nudibranchs do not care for either the eggs or young.

Nudibranchs play an important part in the food web both as predators of soft corals, sea anemones, tunicates, and sponges and as prey of other nudibranchs, sea slugs, crabs, lobsters, turtles and humans. Nudibranchs spend much of their day grazing or prowling for food.

An animal with a soft body makes a tempting target for predators. To protect themselves, nudibranchs employ a number of adaptations. Some nudibranchs blend in with their environment using camouflage or mimicry. Predators have a hard time seeing a nudibranch when it blends in with the sponge or coral it is crawling upon. Other nudibranchs are brightly colored to warn potential predators that they are distasteful or toxic. Nudibranchs can give off offensive tastes and odors depending on what they have been feeding on. Once predators have had a bad experience with a nudibranch they tend to avoid a second encounter. A few nudibranchs can feed on animals with stinging cells like corals and jellies. The stinging cells can move into the cells of the nudibranch without being digested and pass on their ability to sting.

The average lifespan of nudibranchs is about one year.

Conservation efforts should create, maintain, and manage marine protected areas to prevent habitat destruction—particularly at reefs. The establishment of support programs that mitigate the effects of global warming which affects the range of nudibranchs should be prioritized. Protective limits need to be managed to restrict overfishing of nudibranch species for the aquarium trade.

The Spanish dancer is a large bright red nudibranch which has the ability to swim from one location to another by flexing its entire body back and forth. The movement resembles the back and forth movement of the skirt of a Spanish flamenco dancer.

The blue glaucus (blue dragon), unlike most nudibranchs that crawl along the bottom, floats near the surface of the ocean. At the surface it feeds on the stinging cells of the Portuguese man o’ war. These stinging cells can move through the body of the animal without being digested. The cells settle in the tissues of the animal and if touched can give a powerful and painful sting as if you touched the Portuguese man o’ war itself.