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The Largest Animal Group on Earth — Reading Comprehension

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This educational passage, audio-integrated for accessibility, delves into the incredible world of arthropods, Earth's largest animal group. Students will learn about their defining characteristics, such as exoskeletons and segmented bodies, and explore their immense biodiversity. The text explains concepts like metamorphosis and how these creatures have adapted to nearly every habitat on Earth, from the deep oceans to the highest mountains. Aligned with NGSS MS-LS4-1, this passage helps students understand the diversity of life forms and how they have changed over time, providing foundational knowledge about the animal kingdom.

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Colorful arthropods showing exoskeletons, jointed legs, and segmented bodies across diverse habitats. — Arthropods: ants, butterflies, spiders, crabs, and more—Earth’s most diverse animal group.

Imagine a group of animals so vast it includes the tiny ant marching on your picnic blanket, the colorful butterfly fluttering in a garden, and even the majestic crab scuttling on a sandy beach. This incredibly diverse group is called the Arthropods, and they are, without a doubt, the largest animal group on Earth. They make up over 80% of all known animal species!

What makes an animal an arthropod? They share several key features. First, they all have an exoskeleton, which is a hard, outer covering that acts like armor and provides support, much like our bones do. This exoskeleton doesn't grow with the animal, so arthropods must molt, or shed their old exoskeleton, to get bigger. Imagine taking off a suit of armor that's become too small!

Another important characteristic is their segmented bodies. This means their bodies are divided into distinct parts, like the head, thorax, and abdomen in an insect. They also have jointed legs, which is where the name “arthropod” comes from – it means “jointed foot.” This design allows for incredible flexibility and movement, helping them thrive in countless environments.

Arthropods are found almost everywhere on Earth. Insects, a subgroup of arthropods, dominate land environments. Spiders and scorpions, known as arachnids, are also arthropods, often found in dry climates. Crabs, lobsters, and shrimp are crustaceans, living in water. Their ability to adapt to so many different habitats, from deserts to deep oceans, is a major reason for their success. Many arthropods also undergo metamorphosis, a process where they change dramatically in form during their life cycle, like a caterpillar turning into a butterfly. This allows them to use different resources at different life stages.

Their immense biodiversity means they play vital roles in nearly every ecosystem. They pollinate plants, decompose dead matter, and serve as food for many other animals. Understanding arthropods helps us appreciate the intricate web of life on our planet and the incredible variety of forms life can take.

Interesting Fact: Some ancient arthropods, like the extinct sea scorpion Jaekelopterus, grew to be over 2.5 meters (8 feet) long, making them some of the largest arthropods ever to live!

Which characteristic defines arthropods?

Soft, internal skeletonExoskeletonOnly aquatic habitatsNo segmented body

What percentage of animal species are arthropods?

Less than 50%Around 60%Over 80%Exactly 75%

Why do arthropods molt?

To change colorTo grow largerTo attract matesTo digest food

Which of these is NOT an arthropod subgroup?

InsectsMammalsArachnidsCrustaceans

What does 'biodiversity' refer to?

Number of habitatsVariety of life formsAmount of waterSize of an animal

How do arthropods benefit ecosystems?

Pollinate plantsBuild large nestsChange weather patternsCreate new habitats

What is an example of metamorphosis?

A fish swimmingA bird flyingCaterpillar to butterflyA spider building web

If an animal has jointed legs and a hard outer shell, it is likely an arthropod.

TrueFalse

Which term describes a dramatic change in an animal's life form?

AdaptationMigrationMetamorphosisHibernation

Consider an animal that lives in the desert, has eight legs, and sheds its skin to grow. Based on the passage, what type of animal is it most likely to be?

A fishAn insectAn arachnidA mammal