Difference Between Endoskeleton and Exoskeleton

Main Difference – Endoskeleton vs Exoskeleton

Skeleton provides the structural support to animals, facilitating the movements of the body and protecting internal organs. The main difference between endoskeleton and exoskeleton is that endoskeleton is the hard part found inside the body whereas exoskeleton is the hard part found outside of the body. Generally, endoskeleton is derived from the endoderm while the exoskeleton is derived from the ectoderm. Endoderm is the innermost layer and ectoderm is the outermost layer of the three primary germ layers that occur in the very early embryo. Endoskeleton is found in vertebrates and exoskeleton is found in arthropods. Endoskeleton is live and is made up of bones and cartilages whereas exoskeleton, which is a non-living component, is made up of an outer-covering of chitin or calcium compounds. The hydrostatic skeleton is a type of water-based skeleton found in worms.

Key Areas Covered

1. What is Endoskeleton
– Definition, Characteristics, Function
2. What is Exoskeleton
– Definition, Characteristics, Function
3. What are the Similarities Between Endoskeleton and Exoskeleton
– Outline of Common Features
4. What is the Difference Between Endoskeleton and Exoskeleton
– Comparison of Key Differences

Key Terms: Arthropods, Bones, Cartilages, Chitin, Endoskeleton, Exoskeleton, Mollusks, Support, Vertebrates

What is Endoskeleton

Exoskeleton refers to an internal skeleton such as a bony or a cartilaginous skeleton of vertebrates. All vertebrates such as fish, amphibians, reptiles, birds, and mammalians have an endoskeleton. The main function of the endoskeleton is to serve as the internal support system. Endoskeleton is more flexible than the exoskeleton. It provides structural support and protection to the internal organs. It also provides sites for the attachment of muscles. Thus, endoskeleton can transmit forces to the muscles. The endoskeleton of a wolf is shown in figure 1.

Difference Between Endoskeleton and Exoskeleton

Figure 1: Endoskeleton

Endoskeleton is made up of bones and cartilages. In cartilaginous fish, the endoskeleton is exclusively made up of cartilages. A bone consists of concentric rings of bone cells known as osteoblasts. The extracellular matrix is made up of calcium phosphate. Bones articulate with each other by forming joints. Some joints are immovable while the others move. Ligaments attach bones to other bones. Tendons attach muscles to the bones.

What is Exoskeleton

Exoskeleton refers to the external skeleton such as chitinous skeleton in arthropods. Arthropods such as insects, crustaceans, arachnids, Chilopoda, and Diplopoda consist of an exoskeleton. Exoskeleton also provides support to the body and protection to internal organs. The wings of the insects are attached to the exoskeleton through muscles. However, exoskeleton does not grow as the body grows. It is shed several times during the life cycle of arthropods in a process known as molting. A molted exoskeleton of a mantis is shown in figure 2.

Main Difference - Endoskeleton vs Exoskeleton

Figure 2: Molted Exoskeleton of a Mantis

Mollusks also possess an exoskeleton in the form of a hard, protective outer-covering. The exoskeleton of mollusks is made up of calcium compounds except for chitin. Some reptiles such as turtles also possess a hard exoskeleton as mollusks. The exoskeleton of both mollusks and reptiles is not shed during growth.

Similarities Between Endoskeleton and Exoskeleton

Endoskeleton and exoskeleton are two types of hard structures in animals.
The main function of both endoskeleton and exoskeleton is to provide structural support.
Both endoskeleton and exoskeleton aid the movement of the body and protect internal organs.

Definition

Endoskeleton: Exoskeleton refers to an internal skeleton such as the bony or cartilaginous skeleton of vertebrates.

Exoskeleton: Exoskeleton refers to an external skeleton such as the chitinous skeleton in arthropods.

Structure

Endoskeleton: Endoskeleton is made up of calcium and phosphorus.

Exoskeleton: Exoskeleton is made up of scales, chitinous cuticle or calcified shells.

Internal/External

Endoskeleton: Endoskeleton present inside the body.

Exoskeleton: Exoskeleton present outside the body.

Found in

Endoskeleton: Endoskeleton is found in vertebrates.

Exoskeleton: Endoskeleton is found in arthropods.

Composition

Endoskeleton: Endoskeleton is made up of bones and cartilages.

Exoskeleton: Exoskeleton is made up of chitin or calcium compounds.

Living/Non-living

Endoskeleton: Endoskeleton is a living structure.

Exoskeleton: Exoskeleton is a non-living structure.

Development

Endoskeleton: Endoskeleton develops from the endoderm.

Exoskeleton: Exoskeleton develops from the ectoderm.

Growth

Endoskeleton: Endoskeleton grows as the body grows.

Exoskeleton: Exoskeleton does not grow with the body. So, it has to be shed over time.

Flexibility

Endoskeleton: Endoskeleton is more flexible than the exoskeleton.

Exoskeleton: Exoskeleton is less flexible.

Attachment of Muscles

Endoskeleton: Endoskeleton provides structures for the attachment of muscles.

Exoskeleton: The wings of insects are attached to the exoskeleton through muscles.

Conclusion

Endoskeleton and exoskeleton are two types of hard structures in animals that provide structural support. Endoskeleton is an internal skeleton made up of calcium phosphate. It is found in vertebrates. The exoskeleton is an external skeleton made up of chitin. It is found in arthropods. The main difference between endoskeleton and exoskeleton is the occurrence of the skeleton in the body of animals.

Reference:

1. Skeletons in Animals, Cliffnotes, Available here.

Image Courtesy:

1. “1033686” (CC0) via Pixabay
2. “Mantis exoskeleton” By RudiSteenkamp – Own work (CC BY-SA 4.0) via Commons Wikimedia