Going forward including this one fall under the

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going forward including this one fall under the phylum chordata, and it is occupied by species like lancelets. Species that fall under this category are marked by a notochord at least at some point in their developmental cycle, as well as, dorsal hollow nerve chords and a post anal tail. The third branch represents species like lamprey, or more specifically, a division called petromyzontida. Species in this clade are known for possessing a fully formed cranium and head, as well as a vertebral column. Lampreys are also most notably jawless which is what primarily separates this clade from the ones proceeding it. The fourth branch denotes the perch species due to the presence of jaws and lungs. The presence of both of these traits is the main factor that separates them from lampreys, the clade right before this one. Perch and other similar species of this clade, also uniquely possess a swim bladder which allows for more ease when swimming for marine animals. The next branch indicates the distinct class of organisms known as amphibians. This includes the many species of frogs, and for this specific clade, they are made distinct from the groups before by the fact that they are tetrapods. This means they are organisms with four limbs, this is a considerable difference from the species listed prior as they contained no limbs to fins. Amphibians also possess semi-permeable skin causing them to prefer moist habitats. The penultimate branch is made distinct by the ability to produce amniotic eggs. All prior groups have non-amniotic eggs, this means they lack a tough outer egg shell that protects against potential harm or threats. The organisms included in this are the chicken egg and snake, which means that both reptiles and mammals fall under this clade. The final branch is significant since all organisms following possess a synapsid skull which means they only possess one fenestra behind the eye. Skulls with this unique trait are found among large group of Mammalia.
Patrick Williams Lab 8 Deuterostomes BIOL 112 - 504

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