The world we live in today is full of an exceptional variety of animals. The time it took to arrive at the different types of species seen today spanned a period of millions of years. The vast majority of these animals are accredited for evolutionary advancements. When the environment changes, organisms become accustomed to adapting to their environment, to ensure that their species does not die out. These physical changes gave rise to different phyla, ranging from basic structures, like sponges, to advanced systems, like that of an octopus. Porifera is the most simplistic phylum in the kingdom Animalia. Sponges do not have layers of tissue, but rather an inner and outer layer with a gelatinous middle layer separating the two. They constitute the only phylum with asymmetric symmetry. Throughout the advancement of the phyla, it will be shown that this trait is lost. Porifera does not have a proper digestive system, but a system of canals allows the sponges to filter their food. Inside a sponge, flagella pump water through the body of the sponge. This process brings in oxygen and other small organisms, then flows through the top of the sponge, the osculum, removing waste by diffusion. Sponges do not have a circulatory system, as do most early phyla. A coincidental factor could be their small size. It also lacks a nervous system, but very basic nerve cells located in the pores detect water currents. Gas exchanges take place through these pores. Reproduction in sponges can be asexual by budding, gammatation or fragmentation. Some sponges can also have sexual reproduction when an egg is released and fertilized in open water by free-floating sperm. After this stage, they cling to the rock and begin their sessile, basic life....... middle of paper ......d female reproductive organs. An egg is fertilized when it rubs against the clitellum. Earthworms play an important role in the environment. They break down organic matter and dig tunnels beneath the soil that help increase the flow of water and oxygen. Throughout the different phyla discussed, evolutionary progress is relevant. From the basic, simplistic life forms of a sponge, to the intelligence of an octopus and the advanced organ systems of Annelida, the changes have only gotten better. Some species have changed and evolved because as populations grow, they range further and different conditions begin to affect their lives. The reason some species have not changed is because their body plan and system functions according to the environment in which they inhabit. Evolution has helped animals disperse all over the world and adapt to various conditions, as evidenced by the habitats in which Aschelminths can thrive..