Sea sponges are not at all like animals, so even scientists have long considered them to be plants.
Sponges live on the seabed, attached to rocks, shells or sunken ships. They can be of very different shapes. Some species grow like bushes. Others look like bowls, domes, or pipes. Sponges have no heads. they have no mouth, no heart, no stomach, not even a nervous system: the sponge can be cut in half, and it won’t even pickle. Inside it is only elastic porous tissue penetrated by many channels. Why do sponges belong, even to the simplest, but still animals? It's all about the way you eat. Oddly enough, motionless sea sponges “hunt” for their prey - aquatic microorganisms. Sponges do not need to worry about food - in the sea water is full of tiny creatures that are not visible to our eyes. Sponges suck "prey" over the entire surface of the body. Water passing through the pores gets into special chambers. There, special cells capture nutrient particles and digest them. In the same way, the sponges breathe by absorbing oxygen dissolved in water.
Sea sponges come in a variety of sizes: from a couple of centimeters to a meter in height or width.