Taxonomy is the method by which all animal species can be classified, with a hierarchical system that uses at least seven of the 12 classifications from Kingdom to Species. One example that uses human beings is as follows:
- Kingdom - Animalia
- Phylum - Chordata
- Subphylum - Vertebrata
- Class - Mammalia
- Subclass - Eutheria
- Order - Primates
- Suborder - Anthropoidea
- Family - Hominidae
- Subfamily -
- Genus - Homo
- Species - Homosapiens
- Subspecies -
At a very basic level of classification, true animals can be largely divided into three groups based on the type of symmetry of their body plans, radial symmetry which can be divided into two or more planes, bilateral symmetry which can be divided into two halves, and asymmetry, where symmetry can not be achieved.
Architectural patterns in animals are separated into 5 major grades of organization, beginning with single-celled organisms and increasing in complexity to organ systems.
the first grade, the protoplasmic grade, contains organisms where all of their life functions are contained within one cell. for example, species from the genus Amoeba are unicellular with no symmetry, and within its cytoplasm contains organelles that each perform their own specialised function. Like a food vacuole, where food is digested for the cell's nutrition.
the second grade of organization, the cellular grade, is when a number of cells combine but each cell is specialized to perform its own unique function such as nutrition or reproduction. An example of a multicellular organism is the sea sponge, phylum Porifera, which has cells called choanocytes which are flagellated collar cells that trap food particles, and cells that form spicules of calcium to stiffen the sponge.
The third grade is the tissue grade, where cells aggregate and form tissues that function in a unified way. Phylum Cnidaria are placed in grade which includes the radially symmetrical jellyfish. Jellyfish show an organization of tissues by the nerve net, the most primitive form of a nervous system.
The fourth grade is tissue-organ organization. This is more complex than the previous grade as organs are made up of more than one tissue. Super phylum Lophotrochoza, “worms”, are an example of this grade and are the simplest animals to obtain bilateral symmetry. They have an organ system level of organization with the centralization of a nervous system.
The final grade is the organ-system organization. Organs integrate into systems to perform more complex functions like circulation, respiration, and digestion. Many animals have this organization with the simplest being roundworms, phylum Nematoda, which have a complete digestive tract.
As complexity increases, there are additional ways to classify animals. Multicellular animals are often divided into vertebrates and invertebrates. the prevailing view holds that the phylum Chordata consists of 3 Sub-phyla; Eurochordata, Cephalochordata, and Vertebrata. which are all characterized by having a notochord, dorsal tubular nerve cord, pharyngeal pouches/slits, endostyle, and a post-anal tail. Although some of these features may alter or disappear in later stages.
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Essay on Diversity in Animals.
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