Cnidaria Excretory System

Instructor: Heather Pier

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

What is a Cnidarian? What do they eat? And how is the waste from their digestive and bodily processes removed from their bodies? Learn the answers to these questions in this lesson.

What Is a Cnidarian?

Like the famous children's book says, everybody poops! Even a Cnidarian. But they're an odd bunch, so how does it work?

Recall that a cnidarian is an animal belonging to the phylum Cnidaria. All members of the phylum Cnidaria are aquatic invertebrates that can be found in various freshwater and saltwater environments.

The most well known cnidarians are jellyfish, corals, and sea anemones - all of which would probably have a hard time catching food without special stinging cells called cnidocytes. These special cells are used to sting other creatures, both in defense and to catch food.

Many coral reef dwelling creatures are cnidarians, including corals and anemones.

What Do Cnidarians Eat?

Cnidarians aren't the most efficient predators, so for the most part they stick to eating microscopic plants and animals that happen to float past them in the water. These microscopic foods are called plankton.

Some cnidarians, like the larger jellyfish and anemone species, can use their stinging cells to catch larger animals (like fish) to eat. Most corals get their food from symbiotic algaes that live within their hard coral skeletons.

Some jellyfish can actively hunt, but most simply pick microscopic food particles out of the water column.

What is an Excretory System?

Just like humans, cnidarians have an excretory system. The excretory system is the body system responsible for removing wastes materials and fluids from an animal's body.

In humans, this is the system that removes urine, feces, and other metabolic wastes from our bodies. In cnidarians, the excretory system functions in much the same way.

Anemones have excretory systems too

The Cnidarian Excretory System

Unlike us, cnidarians have very few excretory structures. Food is ingested through a mouth and passed into a central digestive region known as the coelenteron. This area is similar to a human's stomach. It is where foods are broken down using enzymes, and nutrients are sent to various cells of the body to be further broken down as needed.

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