Invertebrates are animals that don’t have spines. There are many different types of invertebrates including insects, octopi, jellyfish, and many more. It’s even been estimated that up to 97% of all species of animals are invertebrates. Invertebrates also appear to be the oldest type of animals on the planet. Scientists have discovered fossils of invertebrates that are 665 million years old and some paleontologists believe that they may have appeared on the planet as early as 1 billion years ago.