With this exercise, we will begin to examine the fossilizable members of Kingdom Animalia.
Animals are also the only organisms to have developed nervous tissue and muscle tissue.
Three of the most primitive animal groups are the porifera, archaeocytha, and stromatoporoidea. The sponges are the simplest form of multicellular life, a loosely integrated assemblage of cells that secrete a shared porous skeleton. They have none of the internal organs, nervous tissues, or circulatory and digestive systems that occur in more advanced invertebrates. These cells create currents with a whip-like flagellum to bring in seawater containing food and oxygen and remove waste out the internal cavity, or spongocoel, and through the opening at the top, the osculum. All adult sponges are sessile filter feeders.