Animals are classified into various groups based on shared characteristics,https://dreamsbio.com/seeing-rat-in-dream-during-pregnancy/ including vertebrates (animals with a backbone) and invertebrates (animals without a backbone). Some common groups of animals include mammals, birds, reptiles, amphibians, fish, insects, arachnids, mollusks, and annelids. Animals play crucial roles in ecosystems as predators, prey, and ecosystem engineers. They contribute to nutrient cycling, pollination, seed dispersal, and maintaining ecological balance. Additionally, animals have been domesticated by humans for various purposes, such as food, transportation, companionship, and labor.