Essay --

The world we live in today is full of an exceptional variety of animals. The time it took to conclude to the various sorts of species seen today has been throughout a period of millions of years. The vast majority of these animals are accredited to evolutionary advancements. When the environment changes, organisms have become accustomed to changing to fit their environment, to ensure their species does not die off. These physical changes have resulted in different phyla, ranging from basic structures, like sponges to advance systems, like that of an octopus. Porifera is the most simplistic phylum under the kingdom Animalia. The sponges have no tissue layers, but instead an interior and exterior layer with a gelatinous middle layer that separates the two. They are the only phylum with asymmetrical symmetry. Throughout the advancing phyla it will be shown this trait is lost. Porifera lacks a proper digestive system, but a canal system allows the sponges to filter feed. Along the inside of a sponge, flagella pump water through the sponge’s body. This process brings in oxygen and other small organisms and then flows out the top of the sponge, the osculum, removing waste by diffusion. Sponges lack a circulatory system, as does many of the first couple of phyla. A coinciding factor could be their small size. A nervous system is also missing, but very basic nerve cells within the pores sense the water currents. Gas exchange occurs through these pores. Reproduction in sponges can be asexual by budding, gammation, or fragmentation. Some s ponges can also have sexual reproduction occur as an egg gets released and fertilized in the open water by free floating sperm. After this stage they cling onto rock and begin their sessile, basic, life.... ...d female reproductive organs. An egg becomes fertilized when they rub clitellum. Earthworms play an important part in the environment. They break down organic matter and dig tunnels under the soil that help increase water and oxygen flow. Throughout the various phyla discussed evolutionary advancements are relevant. Starting from the basic, simplistic life forms of a sponge, up to the intelligence of an octopus and advance organ systems of Annelida the changes have only improved. Some species changed and evolved because as populations grow, they spread out farther and different conditions begin to affect their life. Why some species haven’t changed is because their body plan and system works for the environment they inhabit. Evolution has helped animals spread out all over the world and adapt to various conditions, seen in the habitats Aschelminthes can prosper in.