Invertebrates make up between 95 and 97 percent of all animal species on Earth. They play a number of hugely important roles in their ecosystems, such as food, pollination and decomposition. Invertebrates are the planet's biggest source of biodiversity and can be found on every level of the food chain.
Many insects and other invertebrates are the primary food source for a large number of birds, fish, mammals, reptiles and amphibians. There are also many invertebrates higher up the food chain, such as spiders, that only eat other invertebrates. Many insects, such as bees and flies, help support the entire ecosystem through the pollination of flowers, while other species carry plant seeds to help spread the species.
There are approximately 1.3 million known species of invertebrates in the world. Many scientists estimate that there may be as many as 7 million more species that have yet to be classified. The largest group of invertebrates belong to the Anthropoda phylum, which includes insects, arachnids and many other species.
Invertebrates can be found in every ecosystem on the planet, including oceans, lakes and rivers. Some of the aquatic groups of invertebrates include mollusks and crustaceans, such as shrimp, squid, clams, octopus and crabs.