Nudibranchs - Splendid Sea Slugs
View the video "Nudibranchs" to learn about the adaptations of nudibranchs - colorful sea slugs with a remarkable means of defense.
Watch it online.
Video length: 1 minutes 52 seconds
Nudibranchs are sea slugs. They are soft-bodied animals, and like clams, snails and squid, they are mollusks. Nudibranchs belong to phylum Mollusca, class Gastropoda, order Nudibranchia. Found in oceans all over the world, they range in size from .25 inch to longer than a foot. There are more than 3,000 known species of nudibranchs, and they come in all colors, from bright blue to pink to white with orange polka dots.
Nudibranchs get their name from the feathery gills exposed on their backs. The word nudibranch actually means "naked gills." The two most common groups of nudibranchs are the dorids and aeolids. Dorids have a circular tuft of gills on their back that can be withdrawn into their body. Aeolids have fingerlike projections, called cerata, that function as gills and are always exposed. Cerata also contain branches of the digestive tract.
To find food, nudibranchs use their rhinophores - organs that sense chemical signals in the water. Most dorid nudibranchs feed on sponges that contain unpleasant or toxic chemicals. The nudibranchs aren't harmed by the chemicals, but instead incorporate them into their own bodies, making the nudibranchs taste as bad as the sponges. Some nudibranchs can also secrete these chemicals when disturbed. Aeolids, on the other hand, eat cnidarians, a group that includes anemones, corals, hydroids and jellies. Cnidarians have stinging cells, called nematocysts, which are used for defense. Aeolid nudibranchs have the amazing ability to consume cnidarians without causing the nematocysts to fire. Instead, the nematocysts get passed up to the tips of the nudibranchs' cerata and stored, where they then work as the nudibranchs' defense mechanism.
The nudibranchs' bright contrasting colors advertise to potential predators that they are unpalatable. This is called warning coloration. Other animals, including flatworms and nontoxic nudibranchs, have evolved to mimic the colors of the nudibranchs in order to be left alone. In some cases, these colors, even bright ones, help nudibranchs hide by enabling them to camouflage perfectly with their sponge or anemone prey. Since nudibranchs have tiny eyes and most likely don't see much besides light and dark, their colors are not so beneficial for attracting mates, unlike vertebrates. They are hermaphrodites - having both male and female sex organs - and can (and do) fertilize each other reciprocally.
Have students brainstorm a list of colorful animals (e.g., butterflies, birds, frogs, fish). Research and discuss why these animals are colorful. How do they benefit from having bright colors? Review with students what adaptation means and have them describe some adaptations of other animals.
Play the clip with the video turned off so that students only hear the narration. As they listen, have them write down notes about nudibranchs and develop an image in their mind about what a nudibranch might look like. After the clip is done playing, ask the students to each draw a quick sketch. Play the clip again, this time showing the video. Afterward, discuss if anything about the appearance of the nudibranchs was surprising. Let a few students share their drawings with the class.
FOCUS QUESTIONS FOR VIEWING
- Where do nudibranchs get the toxins and stinging cells they have in their bodies? from their prey
- How did nudibranchs get their name? they have feathery gills located on their backs
- What does the word nudibranch mean? naked gills
- How many known species of nudibranchs are there in the world? more than 3,000
- How does the Spanish shawl nudibranch get its color? from its prey
- What do the horn-like appendages, called rhinophores, do? allow nudibranchs to sense chemicals in the water and find food
- What is special about the blue dragon nudibranch? it captures and farms microscopic plants in its body
Discuss the answers to the focus questions. Also discuss why some nudibranchs are so colorful. Use the chart found at the following link to list and describe the adaptations of nudibranchs that were introduced in the video.
Blank Adaptation Chart (PDF)
RELATED RESOURCES FROM JEAN-MICHEL COUSTEAU: OCEAN ADVENTURES
In this video-based lesson, students learn about the unique adaptations of another invertebrate - the sea star - and
then research and develop a presentation on the adaptations of two other organisms.
Students view the video "Squid Spawning" to learn about the short life of the opalescent squid and
then further investigate the habitats and adaptations of squid and their relatives.
Adaptations - What a Concept
Students investigate specific adaptations that allow pink river dolphins to survive in their freshwater
environment, and they construct a concept map to compare and contrast pink river dolphins and marine dolphins.
Little Animals: Big Bag of Tricks, Nan Criqui, Scripps Institution of Oceanography, University of California, San Diego
Ocean Habitats: The Intertidal Zone, "American Field Guide," Oregon Public Broadcasting
Nudibranchs: Marine Slugs With Verve, Dr. Hans Bertsch, The Slug Site
National Science Education Standards Grades 5–8
Life Science –
Content Standard C:
Regulation and behavior
Diversity and adaptations of organisms
Ocean Literacy Essential Principles and Fundamental Concepts:
Essential Principle #5: The ocean supports a great diversity of life and ecosystems.
d. Ocean biology provides many unique examples of life cycles, adaptations and important relationships among organisms (symbiosis, predator-prey dynamics and energy transfer) that do not occur on land.
ABOUT THE AUTHOR
Andrea Swensrud is the KQED Education Network's project supervisor for Jean-Michel Cousteau: Ocean Adventures. She has a Multiple Subject teaching credential and has taught and managed marine science education programs. KQED Education Network uses the power of KQED Public Broadcasting to inspire learning by providing projects for youth and curriculum materials and professional development for teachers, child-care providers and families.
Jean-Michel Cousteau: Ocean Adventures is produced by KQED Public Broadcasting and the Ocean Futures Society. The corporate sponsor is the Dow Chemical Company. Additional major support comes from the Richard and Rhoda Goldman Foundation, KQED Campaign for the Future, and the Corporation for Public Broadcasting.