What are Invertebrates?

Invertebrates are animals that lack a spinal column and can not regulate their own body temperature which makes then cold-blooded. Invertebrates are the most diverse and numerous species on Earth. Many invertebrates have a fluid-filled, hydrostatic skeleton, like the jelly fish or worm. Others have a hard outer shell, like insects and crustaceans. The most common invertebrates include the protozoa, annelids, echinoderms, mollusks and arthropods. Most vertebrates are multicellular, have no backbone, have no cell walls, and have no lungs.

Jellyfish are considered invertebrates.