Animals are multicellular and so are sponges, because they have two distinct layers of cells. To fit the definition of an animal, they need to have animal-like cells. Sponges lack cell walls, which separate them from plants and fungi. Sponges are also eukaryotes, which fits the definition of an animal. Sponges need to take in food for energy, and they can’t photosynthesize. This fact separates them from green plants.
