Sponges are animals, but they can't walk by themselves. They can only attach to rocks on the seabed and get food from the flowing seawater around them. Most sponges live on hard rocks.
Although they can't move, they can already filter food. There are many flagella and a sieve-shaped ring in the pores of the whole body, which can be brought into the sea water by the swing of the whip, bringing in organic debris such as oxygen, bacteria and microalgae, and then filtering through the ring, and finally becoming nutrients for the survival of the sponge. Sponge can't move, but after many changes and disasters on the earth, it can still survive and continue to multiply. Sponge creatures can automatically filter water regularly and absorb nutrients from dead creatures.
Sponges provide protection and waste metabolism for algae, while algae provide oxygen for sponges, which can also be used as food for sponges after algae die.