Invertebrates are creatures without a backbone or similar spinal column, such as bees, spiders, centipedes, lobsters and ticks. They are distinguished from vertebrates, which do possess backbones. Invertebrates are the majority in the Kingdom Animalia, with some estimates saying that 97 percent of animals on the planet are invertebrates.
Invertebrates also lack skeletons made of bone, and they compensate either with a hydrostatic skeleton, as in the cases of jellyfish and earthworms, or they possess a hard exoskeleton, as in the cases of spiders and insects. Hydrostatic skeletons have pressurized liquid inside of them to give form to bodies. Invertebrates with exoskeletons either have one seamless exoskeleton or different components connected by muscle. Exoskeletons provide a degree of protection by encasing delicate internal organs within a hard outer shell.
Despite their unique characteristics, invertebrates share many of the same features as their vertebrate cousins. They are multicellular, thus distinguishing themselves from bacteria, and like other animals, their individual cells lack cell walls. Invertebrates are heterotrophs, meaning that they gather food from the outside rather than manufacture it inside themselves as plants do. Most invertebrates reproduce by means of two individuals of a species contributing gametes for the formation of new offspring.