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Annelids and Arthropods

Annelids and Arthropods

Introduction: Annelids and arthropods are two of the main groups of invertebrate animals. 

Annelids are the segmented worms. Their bodies are divided into individual segments and some species have bristles on their surface to help them move through the soil. Their main function in the ecosystem is to recycle decaying matter. They eat all of the detritus in the soil, which after passing through their digestive systems, is high in nutrients. They also keep the soil aerated. This earthworm is an example of a common annelid.

The arthropods are the largest category of animals on Earth. This group includes the insects, crustaceans (lobsters and crabs), spiders, and millipedes. They have an outer shell called an exoskeleton to protect their bodies (this is why they go "crunch" when you step on them). They also have jointed legs that allow them to maneuver over many different surfaces and also different numbers of antennae.

This grasshopper is an example of an arthropod. It is classified as an insect because it has six legs and one pair of antennae. Its relatives in the ocean, called crustaceans, can have 10 legs and two pairs of antennae. Lobsters and crabs are in this group.

Directions for this Lesson: Answer the practice questions and then watch this video to learn more about the annelids and the arthropods.

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