Samuel GradinaruBIO 1124/5/16Evolution of Kingdom Animalia Animals in our society today are very complicated and complex. Many of their traits and characteristics are the effect of evolutionary change in competition and environmental changes. The first multicellular organisms have been presumed to have evolved around 900 million years ago from a single celled organism. One of the theories of modern day animals is the based on themodern single celled choanoflagellates (O'Brien 2014).Modern day choanoflagellates are very similar to a sponges feeding cells, the chanocytes.Sponges were the first multicellular life. Sponges are asymmetrical and lack true tissue, which caused a lack complexity. Phylum Cnidarian were the first organisms to have true tissue. This allowed them to gain complexity and develop a primitive nervous system. The cnidarian were also the first diploblastic organisms and allowed them to have multiple tissue layers (Harris-Haller 2016).The next major group of organisms that developed were the Ecdysozoa. This group contains nematodes, arthropods and vertebrates. Ecdysozoa were the first triploblastic organisms and when the two types of embryonic development arose. All Ecdysozoa are protostomes.