Jawless, Cartilaginous, and Bony Fish: A Classroom Guide

Fish are one of the most diverse groups of vertebrates on Earth, but not all fish are built the same way. In fact, every species—whether it’s a tiny goby or a massive whale shark—belongs to one of three major groups: jawless fish, cartilaginous fish, or bony fish. Understanding these groups can help students make sense of fish anatomy, evolution, and the incredible variety they see in today’s oceans. Here’s a quick, classroom-friendly guide to what makes each group unique.

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Jawless Fish (Agnatha)

The sucker-like mouths of lampreys, a jawless fish.

Fish were among the earliest vertebrates to evolve, and some ancient fish lived long before jaws existed. Today, the descendants of those early jawless vertebrates survive as lampreys and hagfish.

Jawless fish share the following traits:

Gills
Live in water
Fins (various shapes, sizes, and numbers)
Skeletons made of cartilage, not bone
No jaws
A spine

Since they have no jaws, lampreys and hagfish must feed in some creative ways. For example, lampreys use a round, suction-like mouth with rasping teeth. Some species, like the sea lamprey, are parasites that attach to other fish and feed on their blood and body fluids. Their unusual anatomy makes them an important group for studying early vertebrate evolution.

Cartilaginous Fish (Chondrichthyes)

Like all cartilaginous fish, a hammerhead shark has a skeleton made of soft cartilage. Photo by Ben Phillips on Pexels.com

Unlike jawless fish, cartilaginous fish have a jaw. Jaws allow some fish to hunt and eat larger prey animals. For example, sharks are among the most fearsome predators of the ocean and hunt other fish with their jawed mouth filled with sharp, pointy teeth. Cartilaginous fish are named for their skeletons, which are made of soft cartilage – the material in your nose and ears – instead of hard bone.

Cartilaginous fish share the following traits:

Gills
Live in water
Fins (various shapes, sizes, and numbers)
Skeletons made of cartilage, not bone
Jaws
A spine

There are three main types of cartilaginous fish: sharks, skates, and rays. Though skates and rays don’t look much like other fish, they share a common ancestry and have traits that all fish share, like gills and fins.

Here are some examples of cartilaginous fish:

Great white shark
Leopard shark
Whale shark
Goblin shark
Manta ray
Common stingray
Common skate

Bony Fish (Osteichthyes)

Bony fish are found in many different habitats: from coral reefs in the ocean to flowing freshwater rivers. Photo by Francesco Ungaro on Pexels.com

What do salmon, seahorses, eels, and even your pet beta all have in common? They are all bony fish! This is a vast and diverse group of fish, with many deviations from the classic fish body plan that allow different fish to adapt to their unique habitats.

Bony fish share the following traits:

Gills
Live in water
Fins (various shapes, sizes, and numbers)
Skeletons made of bone, not cartilage
Jaws
A spine

There are two main subgroups within the bony fish group. They are lobe-finned fish and ray-finned fish. Lobe-finned fish have fins with internal bones that move more similarly to the limbs of tetrapods. Meanwhile, ray-finned fish have fins supported by many thin, bony filaments called rays.

There are tons of examples of bony fish. Here are a few:

Lobe-finned fish:
- African lungfish
- Australian lungfish
- African coelacanth
Ray-finned fish:
- Gar
- Sturgeon
- Salmon
- Tuna
- Clownfish
- Seahorse
- Pufferfish
- Eel

Study vertebrates with Wild Earth Lab!

There’s no need to scramble to put together the perfect lessons for teaching fish and other vertebrate groups – I’ve already created them for you! These sets include all the printable materials you need for studying fish and other vertebrate groups in your classroom: