Sponges are the simplest multicellular animals in the world. Because of their plant-like appearance and their presence at the bottom of oceans or lakes, sponges were thought to be plants for thousands of years, but they were later found to possess almost all of the most basic animal characteristics and were classified as animals in the mid-19th century.
The shape of sponge groups varies greatly, and the monomers are generally pyramid-shaped, disc-shaped, goblet-shaped, spherical and so on. The size varies from a few millimeters to 2 meters. Most have calcareous, siliceous or keratinous bones.
The shapes of sponges are varied, including sheet, block, spherical, fan, tube, bottle, pot, and branch, with various postures.