Urmetazoan

Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. The Urmetazoan is the hypothetical last common ancestor of all animals. It was undoubtedly marine, but beyond this its form is difficult to determine; five different hypotheses have been put forward, and discriminating between them is difficult because the relationships of animal phyla are not completely resolved.Animals are considered by biologists to have evolved from a flagellated eukaryote. Their closest known living relatives are the choanoflagellates, collared flagellates that have a morphology similar to the choanocytes of certain sponges. Molecular studies place animals in a supergroup called the opisthokonts, which also include the choanoflagellates, fungi and a few small parasitic protists. The name comes from the posterior location of the flagellum in motile cells, such as most animal spermatozoa, whereas other eukaryotes tend to have anterior flagella.