We are independent & ad-supported. We may earn a commission for purchases made through our links.
Advertiser Disclosure
Our website is an independent, advertising-supported platform. We provide our content free of charge to our readers, and to keep it that way, we rely on revenue generated through advertisements and affiliate partnerships. This means that when you click on certain links on our site and make a purchase, we may earn a commission. Learn more.
How We Make Money
We sustain our operations through affiliate commissions and advertising. If you click on an affiliate link and make a purchase, we may receive a commission from the merchant at no additional cost to you. We also display advertisements on our website, which help generate revenue to support our work and keep our content free for readers. Our editorial team operates independently of our advertising and affiliate partnerships to ensure that our content remains unbiased and focused on providing you with the best information and recommendations based on thorough research and honest evaluations. To remain transparent, we’ve provided a list of our current affiliate partners here.

What Is an Endoskeleton?

By C. Mitchell
Updated Jun 04, 2024
Our promise to you
All Things Nature is dedicated to creating trustworthy, high-quality content that always prioritizes transparency, integrity, and inclusivity above all else. Our ensure that our content creation and review process includes rigorous fact-checking, evidence-based, and continual updates to ensure accuracy and reliability.

Our Promise to you

Founded in 2002, our company has been a trusted resource for readers seeking informative and engaging content. Our dedication to quality remains unwavering—and will never change. We follow a strict editorial policy, ensuring that our content is authored by highly qualified professionals and edited by subject matter experts. This guarantees that everything we publish is objective, accurate, and trustworthy.

Over the years, we've refined our approach to cover a wide range of topics, providing readers with reliable and practical advice to enhance their knowledge and skills. That's why millions of readers turn to us each year. Join us in celebrating the joy of learning, guided by standards you can trust.

Editorial Standards

At All Things Nature, we are committed to creating content that you can trust. Our editorial process is designed to ensure that every piece of content we publish is accurate, reliable, and informative.

Our team of experienced writers and editors follows a strict set of guidelines to ensure the highest quality content. We conduct thorough research, fact-check all information, and rely on credible sources to back up our claims. Our content is reviewed by subject-matter experts to ensure accuracy and clarity.

We believe in transparency and maintain editorial independence from our advertisers. Our team does not receive direct compensation from advertisers, allowing us to create unbiased content that prioritizes your interests.

An endoskeleton is a bone or cartilage-based skeleton that exists wholly inside of an animal’s body. All vertebrates, including humans, have endoskeletons. Echinoderms — a class that includes starfish and some sea anemones — also have this sort of bone structure. It is characterized by a spine from which bones extend, protecting the animal’s internal organs from within.

While never visible on an animal from the outside, the endoskeleton is nevertheless an essential aspect of animal anatomy. It is completely contained within the body, and grows as the animal grows. This makes it different from an exoskeleton in several respects.

Many insects and crustaceans have exoskeletons, which are tough, shell-like structures that cover the body from the outside. These structures are static, which means that they do not grow. Animals with exoskeletons either remain at a constant size throughout their lives or molt their old exoskeletons in order to generate entirely new ones as they grow.

In contrast, endoskeletons are permanent parts of vertebrates’ bodies. The endoskeleton begins developing in the embryonic stage. Baby animals’ bones are often made of cartilage at first, then turn to bone over time through a process known as ossification. As the animal grows, the bones strengthen, thicken, and elongate until they reach full size.

The skeletal system of vertebrates is characterized by several easily identifiable parts. First is the spine. All endoskeletons are built around a stacked spine of joined discs formed as a column that houses the animal’s central nervous system.

At the top of the spine is a skull, which houses the brain. The only exception to this rule occurs with echinoderms. Echinoderms do not have skulls or brains. Their movements are controlled wholly by their central nervous system.

Limbs, fins, and any other extremities also extend from the spine. In most animals, the endoskeleton is covered in muscles, ligaments, and tissues. These coverings allow the endoskeleton to play a major role in body movement and motor control. The bone structure afforded by the endoskeleton allows the body to stand, sit, bend, and swim with precision.

Organ protection is an equally important endoskeleton function. Vertebrates’ bodies are regulated by an intricate system of internal organs, including hearts, lungs, kidneys, and livers. The endoskeleton protects these organs from damage by shielding them with a “cage” of rib bones.

Echinoderms are again an exception, as these animals largely lack internal organs. Their internal structure is usually based around a system of hydraulic chambers and canals, which move fluids and nutrients throughout the body. These internal chambers resemble the inner workings of a hydrostatic skeleton, which is a flexible, fluid-filled cavity that helps soft-bodied animals like earthworms move. The main difference between an echinoderm’s skeleton and a hydroskeleton is the calcified bone structure.

All Things Nature is dedicated to providing accurate and trustworthy information. We carefully select reputable sources and employ a rigorous fact-checking process to maintain the highest standards. To learn more about our commitment to accuracy, read our editorial process.
Discussion Comments
All Things Nature, in your inbox

Our latest articles, guides, and more, delivered daily.

All Things Nature, in your inbox

Our latest articles, guides, and more, delivered daily.