In some are herbivores and some carnivores,

In this lesson, we take a look at a specific class of fish called Osteichthyes.

We’ll cover the characteristics of its members, see some examples, and find out what makes the two subclasses of this group of fish so unique.

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Classifying Organisms

Have you ever peered into an ocean or lake and thought about all the different types of life that live beneath the surface? It may not look like it from standing on the shore, but oceans, lakes, and rivers are teaming with life. Whales, sharks, coral, sea lions, fish, and many other organisms call the earth’s waters home.Just like on land, scientists have classified marine organisms and grouped them based on their similarities and differences. All organisms are divided into interrelated groupings called kingdoms, phyla, classes, orders, families, genus, and species.

The majority of fish fall into one class, called Osteichthyes, which is the focus of this lesson.

Osteichthyes Facts

There are over 25,000 species of Osteichthyes, or bony fish, in the earth’s waters. Most of them have a skeleton made of bone that is much stiffer than cartilaginous fish, which have skeletons made of cartilage, such as sharks. With such an abundance of species, Osteichthyes are the largest group of vertebrates in the world and the largest class of organisms that live in the ocean.

Osteichthyes account for about 96% of all the fish in the sea.Osteichthyes have a keen sense of smell, but unlike other keen-smelling fish, they also have very good eyesight. Osteichthyes eat a wide range of foods: some are herbivores and some carnivores, and some can go long periods without any kind of food at all. In fact, the freshwater eel can go up to a year without food!

Osteichthyes Characteristics

There are exceptions, of course, but generally all Osteichthyes have a variety of shared characteristics.

Since bony fish have a heavier skeleton than cartilaginous fish, they have a special adaptation to keep them from sinking, known as a swim bladder. A swim bladder is a gas-filled organ located under the skeleton. The trapped gas helps keep the fish buoyant, very much like how the air in a life jacket helps you float.

Osteichthyes also have an operculum, which is a bony structure that covers the chambers near the gills on each side of the fish. The operculum allows the fish to breathe without swimming. They move the bone back and forth to pull and push water past the gills, providing them with oxygen.

Other shared characteristics of Osteichthyes include skin with mucous glands, dermal scales, paired fins, and jaws with teeth.

Osteichthyes Subclasses

Osteichthyes are divided into two subclasses: Sarcopterygii and Actinopterygii. Sarcopterygii, or lobe-finned fishes, include the lungfish and the coelacanth, and Actinopterygii, or ray-finned fishes, include salmon, herring, eels, anchovies, and clownfish, among many others.The Sarcopterygii are the least numerous of the Osteichthyes; there are only two types: lungfish and coelacanth. However, scientists believe they share the same ancestor that led to land-dwelling vertebrates.

Amazingly, lungfish can survive for long periods of time in a dry lake bed by surrounding themselves in what is known as a mucus cocoon! At one time, many believed that coelacanth were extinct until they were re-discovered in the early 1900s in a South African lake. They are thought to have evolved from an air-breathing ancestor that lived in shallow water.The Actinopterygii make up the majority of the Osteichthyes; there are thousands of different types.

You can find them in freshwater and saltwater, and they have many different adaptations. Some filter-feed, and some are sit-and-wait predators; some have armor-like scales, and others are able to use their swim bladder as a lung in cases of stagnant water.

Lesson Summary

Osteichthyes, or bony fish, account for about 96% of all the fish in the sea, and have a skeleton made of bone instead of cartilage. There are over 25,000 species of Osteichthyes, with most having the shared characteristics of a keen sense of smell, good eyesight, mucous glands, dermal scales, paired fins, and jaws with teeth.

Osteichthyes also have a swim bladder, or a gas filled organ that helps keep a fish buoyant, and an operculum, or a bony structure that covers the chambers near the gills on each side of the fish and allow it to breathe without swimming.The two subclasses of Osteichthyes are Sarcopterygii, or lobe-finned fishes, and Actinopterygii, or ray-finned fishes. The Sarcopterygii are the least numerous of the Osteichthyes, featuring only two types: lungfish and coelacanth.

The Actinopterygii make up the majority of the Osteichthyes, and include salmon, herring, eels, anchovies, and clownfish, among many others.

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