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Cnidaria Respiratory System

Lesson Transcript
Instructor: Heather Pier

Heather has taught high school and college science courses, and has a master's degree in geography-climatology.

Learn about the respiratory system of cnidarians, the organisms in the phylum Cnidaria. Marvel at how jellyfish, coral, sea anemones, and other members of this phylum can breathe without respiratory organs, and how they gain oxygen from the water. Updated: 11/02/2022


Breathing underwater is impossible for us, so how do underwater creatures do it? Let's look at how the cnidarians take in oxygen even in water.

Cnidarians are some of the most beautiful creatures on Earth. Members of the phylum Cnidaria include coral, sea anemones, jellyfish, and other similar aquatic creatures like sea fans and hydras. Cnidarians are grouped based on the presence of a special type of stinging cell called cnidocytes, which are used for defense and sometimes for capturing food. While almost all live in saltwater environments, there are a few species that can be found in freshwater.

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  • 0:00 Cnidarians
  • 0:48 Respiratory System
  • 1:16 Respiration Without Organs
  • 2:31 Coral Respiration Issues
  • 3:09 Lesson Summary
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Respiratory System

Both humans and cnidarians have respiratory systems. A respiratory system is the body system responsible for taking in needed gases and expelling waste gases. In humans, the needed gas is oxygen, and the waste gas is carbon dioxide. Our lungs and our blood are the primary components of our respiratory system, but how does respiration work in cnidarians?

Respiration Without Organs

Have you ever looked at a jellyfish and wondered where its lungs were? Given their bodies are virtually transparent, you would think that if jellyfish had lungs, we should be able to see them! As it turns out, jellyfish and other cnidarians don't have lungs or any other type of respiratory organ, so it makes sense then that we aren't able to see any obvious lungs when we look at them.

Instead, all of the cells in a cnidarians body are capable of absorbing oxygen from the water around them, and expelling carbon dioxide back into the water through diffusion. Some metabolic wastes can also be passed back into the water through these same cells. Depending on the species, water enters through a mouth or through surface cells, and exits through either location.

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