Invertebrates are animals that lack a backbone or spinal column. They make up about 95% of all animal species on Earth and include a wide variety of organisms such as insects, spiders, crustaceans, and mollusks. Invertebrates can be found in nearly every habitat, from deep oceans to deserts, and they play crucial roles in ecosystems, including pollination and decomposition. These animals exhibit diverse body structures and sizes, ranging from tiny nematodes to large squid. Invertebrates can be classified into several groups, including arthropods, cnidarians, and echinoderms. Their adaptability and variety contribute significantly to the planet's biodiversity and ecological balance.