In the past people thought sponges were?

In the past, people believed sponges were a type of plant due to their porous, flexible structure and their ability to absorb water. This misconception persisted until scientists discovered that sponges are actually simple multicellular animals belonging to the phylum Porifera. Their unique biological characteristics, such as the lack of true tissues and organs, set them apart from both plants and more complex animals. Today, sponges are recognized for their ecological importance in marine environments and their role in filtering water.