Why are sponges classified as animals rather than plants?

Although sponges are often mistaken for plants due to their lack of movement and plant-like appearance, they are classified as animals because their cellular structures and biological functions align with the animal kingdom.1

Sponges belong to the phylum Porifera, a group of primitive multicellular organisms. Unlike plants, which produce their own food through photosynthesis, sponges are filter feeders that rely on a system of canals and chambers to circulate water and capture food particles. This process is facilitated by specialized flagellated cells called choanocytes, which generate water currents.123

Furthermore, molecular data indicates that sponges share a common ancestor with more complex animals. Their life cycle also supports this classification, as they undergo sexual reproduction involving the production of eggs and sperm, often as hermaphroditic individuals, and progress through a free-swimming larval stage before settling as adults.134