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Reading Levels These books contain three developmentally appropriate reading levels for each grade span.

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Each level of the book conveys similar concepts, images, and vocabulary.

Invertebrates

© Zoonar RF/Zoonar/Thinkstock

Invertebrates

Invertebrates are animals that do not have a spine. While students may be more familiar with vertebrates, it is the invertebrate group that represents over 95 percent of all animals on Earth. This unit explores six groups of invertebrates: poriferans (sponges), cnidarians (e.g., sea jellies and corals), echinoderms (e.g., sea urchins and sea stars), mollusks (e.g., octopuses, snails, and clams), annelids (worms), and arthropods (e.g., insects, spiders, and crustaceans). All invertebrates share several traits, but there is also amazing diversity among invertebrate groups. (For vertebrates resources, find the Vertebrates unit in the Life Sciences domain.)

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