Taxonomy Assignment Example | Topics and Well Written Essays - 1000 words

Taxonomy - Assignment Example As to the development of the fish, the armored fishes developed first, then followed by the jawless fishes, the cartilaginous and finally the bony fish. Lastly, when it comes to the development of their young, mammals can be monotremes, marsupials or placentals. The Phyla that Lack Organs and the Type of Symmetry They Have Among the nine phyla, those that lack organs include Phylum Porifera and Phylum Cnidaria. Phylum Porifera, to which the spongers belong, only have a cellular level of organization. Moreover, Phylum Cnidaria, to which the jellyfish and anemones belong, only have tissues and no organ systems. It is also interesting to note that members of the Phylum Porifera have no symmetry but Phylum Cnidaria have radial symmetry. (Audesirk & Audesirk, 2008) The Phyla that Show Cephalization Among the nine phyla, only six show cephalization. These are the Phylum Mollusca, Phylum, Arthropoda, Phylum Chordata, and the worms – Phylum Platyhelminthes, Phylum Nematoda, and Phylum Annelida. These members of these phyla have a distinct head. (Audesirk & Audesirk, 2008) The Phyla that Have Fewer than Three Germ Layers Not all organisms have the three germ layers. While all other phyla have the ectoderm, mesoderm and endoderm, it is Phylum Cnidaria that does not possess the mesoderm, thus it is called diploblastic. All the other phyla are called tripoblastic by virtue of their having all three germ layers. ... The chilopods and diplopods include all centipedes and millipedes respectively. The insects include dragonflies, butterflies, grasshoppers, crickets, cockroaches, termites, leafhoppers, beetles, bees, mosquitoes, fleas, ants and wasps. (Carter, 1997) The Differences among Fish from the Most Primitive to the Most Advanced The most primitive of fishes – the ostracoderms and placoderms – appeared from the Ordovician and Devonian periods. The ostracoderms were shell-skinned and had a bony plate external to their cartilaginous bodies. The head and upper torsos were covered with a bony armor plate and the back and lower half were cartilage. They also had spikes and a toothless jawless structure. On the other hand, the placoderms, which eventually replaced the ostracoderms, had an armor that covered the entirety of the head and a portion of the body as well. The only difference was that the placoderms had functional jaws, unlike the ostracoderms. (Arreola, 2005) The placoderms were eventually replaced by Class Agnatha, or the jawless fishes, such as lampreys and hagfish, which exist today. They have neither jaws nor a bony skeleton. The Class Chondrichthyes developed next. They have jaws but lack a bony skeleton. Members of this class include sharks and skates, all of which have cartilaginous skeleton and a skin with teeth-like denticles. Finally, the Class Osteichthyes, or the jawed bony fishes, developed last. These fish, with over 20,000 species all over the world, have protrusible jaws and calcified skeletons. (Buchheim, 2011) The Three Types of Mammals Based on How Their Young Develop The three types of mammals based on how their young develop include the monotremes, the marsupials and the placental mammals. The monotremes, which include