If you ask another person what their favorite animal is, the odds are that they’ll mention cats, dogs, cows, wolves, bears, horses, birds, turtles, or even fish. After all, most of the most popular animals are vertebrates or animals with backbones. Although invertebrates like insects, worms, and mollusks go primarily ignored, they’re some of the most abundant animals on Earth!

Invertebrates, or animals without backbones, are important creatures that play unique roles in the environment. Although some look less than cute, there are many beautiful and cool-looking ones, too! If you want to learn more about these animals, keep reading!

Infinitely Interesting Invertebrate Facts to Explore

Most people are interested in vertebrate animals, but we must also learn to appreciate the mysterious beauty of invertebrates. If you have friends and family members who love animals, you can impress them with these facts!

Most Animal Species Are Invertebrates

Much like our beloved vertebrates, invertebrates come in various shapes and sizes. They’re way more diverse than us! Although we might see invertebrates as odd, it turns out that vertebrates are the exception, not the norm.

From what scientists know now, there are around 5,400 unique species of mammals and more than 11,000 species of birds on Earth. Group all the vertebrates, and there are above 64,000 species. 

If you think that’s a lot, you’d be surprised how many invertebrate species scientists have recorded so far. Currently, they’ve described over 1.25 million unique species! Mollusks alone has over 100,000 species. Now, that’s a lot of animals to keep track of. 

Courtesy of Nennieinszweidrei

Around 80% of All Living Animals Are Roundworms

If you think the previous fact is impressive, you’re in for a shocker. If you counted every living animal on Earth, you’d find that 80% are tiny invertebrates called nematodes or roundworms. 

These invertebrates are so prominent that for every living person on Earth, there are around 57 billion roundworms to match. If you weigh all of them, it’ll total 300 million tons!

Roundworms can be found in many different places. They can live in grasslands, tundras, deserts, forests, and even seafloor. Some of them are parasitic and cause diseases in humans. Now, that’s an invertebrate fact that’s not too fun.

Courtesy of Couleur

Some Invertebrates Can Survive in Outer Space

One invertebrate is particularly famous for its extraordinary ability to survive extreme conditions, which is the tardigrade or water bear. This near-microscopic invertebrate looks almost like a miniature alien bear with six legs, which many internet users adore.

Although water bears may look nothing more than cute, tiny invertebrates, they can survive the coldest areas of Antarctica and the hottest thermal vents on the seafloor. They can even survive strong radiation and the vacuum of outer space where no other animal can live!

Water bears can survive these conditions by curling up into a tiny, near-indestructible ball called a tun. While in this state, they become inactive until their environment becomes more favorable. 

Courtesy of Encyclopedia Britannica

Most Invertebrates Undergo Metamorphosis

When invertebrates hatch from their eggs, they often don’t look like their parents. Animals like jellyfish, crabs, and many insects have larval forms and transform into different forms as adults.

This transformation is called “metamorphosis.” One prominent example is how caterpillars turn into chrysalises and eventually into butterflies. Metamorphosis also exists in vertebrates, but it’s limited to amphibians (like frogs and toads).

Courtesy of Pixabay

Some Invertebrates Have Skeletons Outside Their Bodies

The defining trait of vertebrates is our backbones, which are part of our skeletal systems. Meanwhile, invertebrates don’t have these. In fact, many of them don’t even have skeletons. Even when they have skeletons, though, they’re not like us.

In one large group of invertebrates, the arthropods (which include crustaceans, insects, and arachnids), the skeletons are outside their bodies. Their tough exoskeletons act like armor and provide them with impressive protection against many things in the environment that could harm them.

Courtesy of Egor Kamelev

The Simplest Animals Are Invertebrates

Some animals are so simple that they barely move or have differentiated organs. These include placozoans, corals, jellyfish, and sea sponges, which are invertebrates.

Don’t be fooled, however, as not all invertebrates are simple. For instance, octopuses, squids, and cuttlefishes are highly complex animals. They have well-developed organs and coordinated nervous systems. They’re also intelligent and skilled at camouflage and even tool use.

Courtesy of Scott Webb

Invertebrates Have Been Around for Longer Than the Dinosaurs

Scientists discovered many fossils consist of bones, which invertebrates don’t have. As such, it’s hard to tell how long they’ve been around. However, scientists have found fossilized soft tissues which belonged to ancient invertebrates. Some of the oldest invertebrate fossils date back to 3.5 billion years, way before the ancestors of dinosaurs even existed!

Courtesy of Lesli Whitecotton

Some Invertebrates Form Large Colonies

Many invertebrates form large groups that work together throughout most of their lives. They help each other feed, reproduce, and even build shelters where many individuals can benefit. 

Some invertebrate ocean colonies are so coordinated that they almost act like giant organisms. On the other hand, invertebrate colonies on land have more independent individuals that have specialized roles (such as bees, termites, and ants).

Courtesy of Egor Kamelev

The Great Barrier Reef Is Made of Invertebrates

If you’re looking for an impressive feat of invertebrate colonies, look at the Great Barrier Reef. This large structure exists outside the northeastern coast of Australia, the largest coral reef system on the planet. Spanning over 133,000 square miles (344,400 square kilometers), it’s so extensive that you can see it from space. 

The Great Barrier Reef is composed of, and built by, billions of tiny invertebrates called corals. Although corals look similar to rocks, they’re living animals! They make these reefs by releasing calcium carbonate deposits that solidify over time. 

Courtesy of Tom Fisk

Invertebrates Multiply Quickly 

Part of why invertebrates are so successful is that they reproduce prolifically. Some species have male and female parts; others can even clone themselves! 

Courtesy of Alexsandro Rosa de Mello

Scientists Study Invertebrates a Lot

Scientists for centuries have largely ignored invertebrates, but modern scientists see the value of these animals as model organisms. We owe much information about genetics to many invertebrate species, such as the common fruit fly and the Caenorhabditis elegans roundworm.

Courtesy of nikita

Most Invertebrates Don’t Have Lungs

The majority of invertebrates don’t have lungs. Instead, they rely on other organs to get oxygen. Most of them use gills, while others have holes called spiracles that let air in their bodies and help deliver oxygen directly into their circulatory systems.

Courtesy of Capture Blinks

For Your Child’s Invertebrate Fascination

Keeping these little critters as pets isn’t always feasible, so consider getting them the following books instead:

• Invertebrate Activity Book For Kids by Lubawi Books
• Classifying Animals into Vertebrates and Invertebrates by Baby Professor
• Invertebrate Zoology For Kids by Ellen Doris

Frequently Asked Questions on Invertebrates

What is the biggest invertebrate?

Invertebrates vary widely in size—some of them are too small to see with the naked eye, but some are bigger than us! The largest known invertebrate is the colossal squid, which can grow to more than 40 feet (12 m) long and weigh over 1,000 pounds (454 kg)!

Do all invertebrates lay eggs?

Most invertebrates lay eggs, but not all of them. Some species of velvet worms, cockroaches, and scorpions give live birth!

Do invertebrates feel pain?

The answer to this question is hotly contested. It’s impossible to determine animals’ subjective feelings, but most evidence points out that most invertebrates don’t feel pain. However, for more intelligent species like octopuses, the consensus is that they’re conscious and can feel pain.