List of Animals
They are characterized by their capacity for locomotion, the absence of chlorophyll and wall cells, and embryonic development, passing through a blastula stage and determines a fixed body plan (although many species can be subsequently metamorphosis). Animals are a natural group closely related to fungi and plants. Animal kingdom is one of the five kingdoms of nature, and humans are included on this kingdom.
Mobility is the most striking feature of the organisms of this kingdom, but is not exclusive to the group, which results that are often referred to certain organisms such as animals belonging to the Protista kingdom.
The following scheme shows the characteristics common to all animals:
- Organization phone. Multicellular eukaryotic.
- Nutrition. Heterotrophic by ingestion (at the cellular level by phagocytosis and pinocytosis), unlike fungi, also heterotrophs but absorb nutrients after digesting them externally.
- Metabolism. Aerobic (oxygen consuming).
- Playback. All species reproduce sexually (some only by parthenogenesis), with very different sized gametes (oogamia) and zygotes (diplonte cycle). Some can also multiply asexually. They are typically diploid.
- Development. By embryo and embryonic leaves. The zygote divides repeatedly by mitosis to give rise to a blastula.
- Structure and functions. Have collagen as a structural protein. Highly differentiated tissue cells. No cell wall. Some with chitin. Phagocytosis in basal forms. Ingestion or absorption with subsequent phagocytosis in derived forms ("more evolved"), capable of movement, etc..
- Symmetry. Except for sponges, other animals show a regular arrangement of body structures along one or more body axes. The main types of symmetry are the radial and bilateral.
With few exceptions, most notably the sponges (Phylum Porifera), animals have differentiated and specialized tissues. These include muscles, which can be contracted to monitor the movement and nervous system, which sends and processes signals. There is usually also an internal digestive chamber, with one or two openings. Animals with this type of organization are known as eumetazoan, as opposed to Parazoa and Mesozoa, which are simpler levels of organization and lack some of the features mentioned.
All animals have eukaryotic cells, surrounded by a characteristic extracellular matrix composed of collagen and elastic glycoproteins. This may be calcified to form structures like shells, bones, and spicules. During development of the animal creates a relatively flexible framework by which cells can move and reorganize, making possible more complex structures. This contrasts with other multicellular organisms like plants and fungi, which develop a progressive growth since its cells remain in place by cell walls.