What separates insects from other groups of invertebrates?

Scientists group invertebrates into eight major phyla, including sponges, cnidarians, worms, mollusks, echinoderms, and arthropods. Many invertebrate phyla may be divided into more than one class

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primary succession occurs in essentially lifeless areas regions in which the soil is incapable of sustaining life as a result of such factors as lava flows, newly formed sand dunes, or rocks left from a retreating glacier. secondary succession occurs