Some people may call invertebrates spineless because they lack a backbone or spine! But these amazing creatures are the most abundant animals on Earth. Some invertebrates, like squid and leeches, have soft bodies, while others, like crabs, have a hard outer shell called an exoskeleton. Invertebrates are found in every ecosystem. Some, such as sponges, jellyfish, starfish, and crabs, live in the ocean.

Characteristics: no backbone, cold-blooded
Habitat: found in all ecosystems, from the Arctic regions to the tropics
Common examples: insects, crabs, octopuses, worms, and jellyfish
Cool fact: ninety-nine percent of all animals on Earth are invertebrates

Image credits: main image, scorpion, courtesy of California Academy of Sciences, Arie van der Meijden, garden slug, courtesy of California Academy of Sciences, William Leonard, jellyfish, courtesy of NOAA, Kip Evans.