Any animal lacking a backbone is an invertebrate. Invertebrates make up most of the animal kingdom. The invertebrates range from the simple SPONGES to advanced animals such as INSECTS and MOLLUSKS. The earliest fossil invertebrates date from Precambrian times (4 billion years ago to about 570 million years ago).

The notorious Portuguese man-of-war jellyfish, pictured here, moves on the surface of warm seas by the force of the wind on its blue, gas-filled float. Stinging tentacles, as long as 20 meters or more, hang from underside of its float. These poison tentacles launch can seriously or fatally injure humans, but more often capture fish.