Essay --

Through an examination of the phyla Porifera, Cnidaria, Platyhelminthes, Aschelminthes (Nematoda), Mollusca, Annelida, and Arthropoda, an obvious pattern of evolutionary advances is present. As one moves across these seven phyla, developments in traits such as methods of acquiring nutrition, the digestive system, the circulatory system, the nervous system, and the gas exchange system could easily be noted. Other observations could be logged regarding the development of the excretory system, the reproductive system, development, body plan, symmetry, and ecological niche. A look at the contrasting qualities of these phyla provides a clear understanding of their evolutionary advances. From filter-feeding to taking in food through the mouth, the methods of acquiring nutrition among the first seven phyla show a distinct evolutionary advancement. In the most basic phylum, Porifera, the sessile sponges receive nutrients through a system of filter-feeding, in which the organism uses its ostia, or pores, and chaonocytes, or flagellated collar cells that create water currents, to filter in water. The organism is then able to remove algae and other food particles from the water in order to acquire its food. In contrast to the phylum Porifera, the next phylum, Cnidaria is composed of carnivorous organisms, so thus they prey on other animals, unlike Porifera (who wait for their food to come to them). Cnidarians have nematocysts, or stinging cells, which allow them to paralyze and kill their prey. They are then able to use their tentacles to bring their food to their mouths. All of the subsequent phyla also take in food using their mouths, and hunt their prey (if carnivorous) using different methods. It is in the following phylum, ... ...opods prey on smaller organisms. Like the Mollusca phylum, there are many arthropods that serve as a food source to humans. Porifera, Cnidaria, Platyhelminthes, Aschelminthes, Mollusca, Annelida, and Arthropoda, the first seven phyla, have a distinct connection in their evolutionary traits. A distinct grasp on the connections between the evolutionary advances of the seven phyla is easily acquired upon looking at the differing aspects of these phyla. In traits like methods of acquiring nutrition, the digestive system, the circulatory system, the nervous system, the gas exchange system, and the excretory system, a distinct line can be drawn from start to finish. In other traits like the reproductive system, development, body plan, symmetry, and ecological niche, one could easily log the improvement as the transition is made across the spectrum of phyla.