Red algae are some of the oldest eukaryotic organisms on the planet.
Fossils of red algae have been found that are over 2 billion years old. There are 4000 different species of red algae. They are very abundant in tropical and warm waters, although many are found in cooler waters. Red algae are typically found in marine waters attached to rocks or other plants in the calmer, deeper waters beyond the tidal zone. Some red algae are reef builders in tropical seas, as important or more important than coral animals.