Animals have two main groups: vertebrates (with a spine) and invertebrates (without a spine). Mammals , birds, reptiles, fishes, and amphibians are the main types of vertebrate animals. Invertebrate animals generally include insects , arachnids (spiders, scorpions, mites, etc.), mollusks (snails, octopus, squid, etc.), and crustaceans (lobsters, crabs , shrimp, etc.). Mammals and birds are warm-blooded animals that can adjust their body temperatures according to their surroundings. All the other animals are cold-blooded. Most animals appeared during the Cambrian period around 540 million years ago, in duration of 20 to 25 million years. It is known as the Cambrian explosion and is the main event used by creationists to deny Darwin’s theory of evolution. ( Source ) Pompeii worm is the earth’s most heat-tolerant animal that can live at a temperature of 176 F (80 o C). The bacteria on its body help the worm to withstand this extremely high temperature. ( Source ) A parasiti
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