Sponges have unspecialized cells that can transform into other types and that often migrate between the main cell layers and the mesohyl in the process. Sponges do not have complex nervous,[6]digestive or circulatory systems like humans. Instead, most rely on maintaining a constant water flow through their bodies to obtain food and oxygen and to remove wastes. Believed to be some of the most basal animals alive today, sponges were possibly the first to branch off the evolutionary tree from the last common ancestorof all animals, which would make them the sister group of all other animals.[5]
The branch of zoology that studies sponges is known as spongiology.[7]