The exoskeleton, jointed appendages, and segmented body of an arthropod make it one of the most easily recognizable groups of animals. Arthropods include crustaceans, insects, spiders, scorpions, and centipedes. These creatures are characterized by their tough outer shell, which protects them from predators and the environment.
Arthropods are also able to move quickly and efficiently thanks to their jointed appendages. Additionally, the segmented body of an arthropod allows it to adapt and change as needed to survive in its environment.
Enjoy this in-depth list of 7 characteristics of arthropods.
Characteristics vs. Traits vs. Adaptations
A characteristic is a fixed quality of an animal, while a trait is a potential way that characters can be expressed. For example, having hair would be a characteristic of humans, while the different hair types as well as genetic or environmentally-caused baldness and albinism would all be traits of that characteristic.
An adaptation is when a certain trait becomes dominant in a population to allow it to survive- for example, brown eyes, longer arms or eating from a certain place on a tree like giraffes do.
7 common characteristics of arthropods
1. Segmented Exoskeleton
One of the most defining characteristics of arthropods is their segmented bodies. Arthropods are invertebrates that have an exoskeleton, or outer skeleton, made up of hard plates. These hard plates are actually modified segments of the arthropod’s body.
The hard plates protect the soft tissues inside and also provide points of attachment for muscles. Arthropods are able to move their bodies because of the way their segments are connected. Each segment has a pair of appendages, which can be legs, antennae, or other body parts, depending on the arthropod.
The appendages are jointed, meaning they can bend at certain points. This allows the arthropod to move its body in different directions.
2. Open Circulatory System
Most arthropods have an open circulatory system. This means that their blood does not flow in vessels, but rather fills a body cavity called the coelom.
The coelom is a fluid-filled space that surrounds the organs and provides them with nutrients and oxygen. The blood of arthropods contains hemoglobin, which gives it a red color.
3. Composition and Shedding of the Exoskeleton
The exoskeleton of arthropods is made up of a tough outer shell called the cuticle. The cuticle is composed of chitin, a substance that is also found in the cell walls of fungi. The cuticle protects the arthropod’s body and helps it to retain water.
Arthropods shed their exoskeleton periodically as they grow. This process, called molting, allows them to increase in size and also to replace any lost appendages.
4. Malpighian tubes, Green Glands & Coaxal Glands
Malpighian tubes are one of the most distinguishing characteristics of arthropods. These long, thin tubes run from the gut to the hindgut, and play an important role in excretion and osmoregulation. Malpighian tubes are highly efficient at removing wastes and toxins from the body, and help to keep the blood and body fluids clean.
They also help to regulate the level of salt and water in the body, which is essential for survival in dry or salty environments. Notably, Malpighian tubes are only used in land arthropods. Aquatic arthropods use green glands or coaxal glands for excretion and osmoregulation.
Green glands are small, round structures that are found in the abdomen. They secrete a greenish-colored fluid that helps to remove wastes and toxins from the body. Coaxal glands are long, narrow tubes that run along the sides of the body.
They also secrete a fluid that helps to remove wastes and toxins, but this fluid is clear or colorless. Both Malpighian tubes and green/coaxal glands are essential for the survival of arthropods.
Without these organs, arthropods would be unable to rid their bodies of waste and toxins, and would quickly succumb to dehydration in dry and salty environments.
5. Diffuse Respiration & Trachea Use
Arthropods breathe using a variety of methods depending on the species. Most arthropods have an open circulatory system, which means that their body cavity is not completely separated from the outside environment. This allows oxygen to diffuse directly into their tissues.
Some arthropods, such as insects, have a series of small holes along their sides called spiracles. They open and close these holes to regulate the amount of oxygen that enters their bodies. Arthropods also have a variety of methods for getting rid of carbon dioxide.
Many species simply allow it to diffuse out through their open circulatory system. Others, such as insects, have special organs called tracheae that carry the gas to and from their tissues.
6. Compound Eyes
Arthropods have compound eyes, which are composed of multiple small eyes, or ommatidia. Each ommatidium contains a lens and a light-sensitive receptor cell. The number of ommatidia in an arthropod’s compound eye varies depending on the species, but can be in the thousands.
Compound eyes allow arthropods to see in multiple directions at once and to detect movement very well. However, they do not provide sharp vision.
7. Reproduction & Metamorphosis
Arthropods reproduce by laying eggs. The eggs hatch into larvae, which then undergo a process of metamorphosis to become adults. Some arthropods, such as insects, have an incomplete metamorphosis, meaning that the larvae and adults look quite different from each other.
Other arthropods, such as crabs and lobsters, have a complete metamorphosis, in which the larvae and adults look very similar to each other.