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The annelids (Phylum Annelida) are also called the segmented worms due to their segmented bodies. This group includes the most familiar of all invertebrate worms. Earthworms, freshwater worms, leeches, and marine worms are all annelids. This group is also called "bristle worms" because most annelids have tiny chitinous bristles called setae. The setae help terrestrial annelids grip their surroundings, and they aid aquatic forms with swimming. Annelids are worldwide in distribution, and they are found in marine environments, fresh water, and terrestrial soil. Some annelids are predators, others are vegetarians, and some leeches are bloodsuckers.

Annelids are a phylum including earthworms, leeches, polychaete worms, and some other worm groups(3). Annelids are also called segmented worms because a defining feature they all share is a body most of which is divided into segments, each of which contains parts of the basic body systems (2). This segmentation, or metamerism, allows annelids to move more efficiently and provides other benefits as well(2). Inside all of these segments, in a cavity known as the coelom, is fluid that presses against the annelid’s body, keeping the body firm so that it can bend and extend without breaking (1,2,3). Although segmented worms may appear simple, the organs inside them are highly developed; various annelids have organs that can sense touch, balance, and chemicals in their environment, and some even have eyes with lenses (2,3). While all annelids share some important physical characteristics, they live all over the world in a huge range of habitats on land and in the water (both freshwater and marine), with varying diets, feeding habits, reproductive methods, and life cycles (2,3).

Annelids: Powerful and Capable Worms Video and Lesson Plans

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Shape of Life is a series of FREE classroom videos based on an original PBS Series. Explore the beautiful evolution of the animal kingdom on planet earth. The series is NGSS aligned with exquisite focus on diversity, biodiversity, adaptability, body structure, design, behaviors, and the innovative scientists who explore these creatures.