You will learn about the many different types of sea animals in this lesson, including how they are classified into different groups and where in the oceans they can be found.

What Makes an Animal a Sea Animal?

Most people probably think they know what a sea animal is. They would probably tell you that they can’t really define what a sea animal is, but they would know one when they see one, like a whale or dolphin.

But what about starfish? Or sea anemones? Or microscopic krill? A sea animal is any type of animal that lives in a body of saltwater (like a sea or ocean), so starfish and krill are just as much sea animals as a whale is.

All sea or ocean-dwelling animals can be further classified based on how they move and where they live.

Nektonic Animals

Sea creatures that are able to swim freely under their own power are classified as nekton. The nekton group of animals includes some of the most classic examples of sea life, including whales, dolphins, and fish.

Unlike other types of sea animals that can only live on the ocean floor or drift in the ocean currents, nektonic animals can move around wherever they want to because they are able to swim.

This clownfish is an example of nekton, while the leather coral is an example of a benthic animal.

This usually means that they are larger and more biologically complex organisms than those that can’t swim, because it requires complex body systems to be able to swim and regulate body position in the water.

In addition to whales, dolphins, and fish, squids and cuttlefish are also examples of nekton.

Planktonic Animals

Plankton are nearly the opposite of nekton in almost every way. Plankton are animals that live in the water column of the oceans but are unable to regulate their position in the water on their own. They drift along to wherever the ocean currents carry them.

They are much simpler biologically, and include many microscopic animals like krill and also the larval form of benthic ocean creatures like coral and sea urchins. Planktonic animals are the wanderers of the sea, going wherever the current takes them.

This is a magnified image of a microscopic planktonic animal.

Benthic Animals

Benthic animals are often not the first animals you think of when you think of sea animals. Benthic animals are animals who are unable to swim, and instead live out their lives on the ocean floor.

Many may have been plankton when they were in their larval stage of life, like starfish, sea urchins, and coral. Coral are, in fact, animals, and given you don’t see coral randomly swimming around the reef, they too are benthic.

Sea cucumbers, bristle worms, lobsters, crabs, and sand dollars are all examples of benthic animals. Almost all benthic creatures can move freely, but some like coral and sea lilies will eventually become fixed in place.

Starfish are one of the best known benthic animals.

Lesson Summary

Sea animals are any animal that lives in a body of saltwater like a sea or ocean. They are classified based on where in the water they live and how they move. Nekton are able to swim freely under their own power, and are usually larger, more complex animals.

Plankton are not able to swim freely, and drift in the ocean currents. They are usually smaller, less complex organisms or larvae. Benthic animals are unable to swim, and live their lives on the ocean floor. Some are able to move freely while others are fixed to the ocean floor.