Sponges are classified under kingdom Animalia for which of the following reasons?

The animal nature of sponges is first described in 1755, was confirmed in 1765 after observations of their water currents and the changes in diameter of the openings into their central cavity. This pathway of water transport is helpful in food gathering, respiratory exchange and removal of waste. In structure, function, and development, sponges are distinct from other animals.

Most plants are also sessile. Asymmetry is not unique to animals. Some protists like Amoeba are also asymmetrical. Organs are absent in most other organisms.