Had to get my Google on for this one, but apparently, new gene-mapping has determined that the very first animal on planet Earth was… [drum roll, please]
…the comb jelly!
We used to think that the first animal was the sponge, but it seems the comb jelly has them beat, and was even surprisingly complex! Unfortunately, though, no fossils are available, so we don’t know quite *when* this was yet.
To add to Lindsay’s answer, that’s the oldest animal that we still have around. We actually know of many animals that are considerably older than that, but have poor fossils, so we don’t know much about what they’re like at all! Our best guesses is that they were all soft and a little shelly, and lived somewhere along shallow sea or ocean floors.