Nine Phyla of the Animal Kingdom - Assignment Example

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 has 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 has 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. The 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 triploblastic by their having all three germ layers. (Pomarico, 2006)
The Phylum that Has More Species than Others

Phylum Arthropoda is the phylum with the most number of species compared to all the other phyla. A subphylum of arthropods, the arachnids, includes scorpions, mites, spiders, daddy-long-legs, and ticks. The crustaceans include crayfish, lobsters, and crabs. 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 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 skeletons and 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 the duck-billed platypus, are those that lay eggs through their cloaca, a single posterior opening in their bodies. As the eggs hatch, the young are fed with milk from the mammary glands and nurtured for as long as one year. (Baines, 2001; Thompson, 2011)

On the other hand, the marsupials, like the opossums, produce very immature young which develop while attached to the nipples in a marsupium or abdominal pouch for one week to one year. The young do not have completely developed hearts, lungs, and eyes. (Baines, 2001; Thompson, 2011)
The placental mammals, to which around 3800 species worldwide would belong, differ from the monotremes and the marsupials because the former would normally give birth to more mature young, which were nurtured for a considerable time before birth. The young are given birth through the urogenital tract and are fed with milk from the mammary glands. (Baines, 2001; Thompson, 2011) Read More