Arachnids Lesson for Kids: Characteristics & Evolution

Instructor: Wendy McDougal

Wendy has taught high school Biology and has a master's degree in education.

Arachnids are a class of animals that includes some well-known creatures. In this lesson, learn more about the characteristics and evolution of some different types of arachnids, such as spiders.

Arachnids

How do you feel when you see a dark, 8-legged creature scamper across your floor? Some people are nearly paralyzed with fright at the sight! We are talking about members of the Class Arachnida (pronounced uh-rak-nid-ah), which includes all spiders big and small. This group contains not only thousands of species of spider, but also some other creepy-crawlies.

Many people do not want to see this running across their floor
Spider

Examples of Arachnids

Let's meet the members of Class Arachnida. Possibly the most well-known members of this group are spiders, ranging from itsy-bitsy spiders to giant tarantulas. Scorpions are another fairly well-known example of an arachnid. This nocturnal desert-dweller carries quite the sting, due to the sharp venomous tip on its tail.

Blood-sucking ticks belong to this group, and they are often found latched onto a dog. Ever heard of dust mites? These microscopic arachnids love to make their homes deep in mattresses and other furniture. And while not a true spider, the delicate daddy longlegs also belongs to Class Arachnida.

Mite under magnification
Yellow mite

Characteristics of Arachnids

Arachnids are a group of animals that belong to a larger group, Phylum Arthropoda (pronounced Fahy-luh-m Ahr-throp-uh-duh). All arthropods, which include insects and crustaceans (pronounced kruh-stey-shuh-n), have important features in common. These include segmented bodies and jointed legs. They also have a skeleton on the outside of their bodies, known as an exoskeleton, which gives them a hard shell.

Arachnids have a 2-part body, including a head with an attached midsection. Unlike insects, arachnids have no antennae protruding from their heads. The other body part is the abdomen, which contains the bodily organs and serves as a base for six pairs of protruding appendages, or attachments. As you probably already know, four of those pairs are legs, giving spiders their trademark eight legs.

Diagram of spider body showing two body parts and four pairs of legs
Spider anatomy

Arachnids also have two more specialized pairs of appendages on their heads. The first pair has a slightly gruesome purpose. Arachnids are avid hunters and predators, so this pair is used for stabbing, grabbing and cutting an unsuspecting victim, or to inject venom. The other two appendages are general mouthparts used for eating.

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