Animals in the sense of modern systematics covers only a multicellular groups and organized in the different functions of the network, so that this group is also called histozoa. All the animals are heterotrophic, meaning not create their own energy, but must take from the surrounding environment.
Animal derived from the Latin "animalis", which means "has a breath". In informal everyday use, the word usually refers to non-human animals.
Sometimes, a close relative of humans such as mammals and other vertebrates addressed in informal usage. Biological definition of the word refers to all members of the kingdom Animalia, encompassing creatures as diverse as sponges, jellyfish, insects and humans.
Here are the characteristics of animals in general:
- Animals are eukaryotic organisms, multicellular, heterotrophic. Unlike the autotrophic nutrition in plants, animals enter the organic material that is so, into the body by means of swallowing (ingestion) or consuming other organisms, or eat organic matter decomposes.
- Animal cells do not have cell walls that support the body with strong, such as in plants or fungi. The largest component of animal cells consisting of the structural protein collagen.
- The uniqueness of the other animals is the existence of two networks that are responsible for conduction of impulses and movements, the nerve tissue and muscle tissue so that it can move actively.
- Most animals reproduce sexually, with diploid stage that dominates the life cycle.
- Respirator in animals vary depending on place of life, there are breathing with lungs like a cat, like fish gills, skin like worms, trachea like insects.
- Requires food to grow and survive.
An early form of animals suspected of flagella-like which then lost the chloroplast and grow to resemble flagellates present. Another theory says animal cells evolved from aerobic eukaryotic cells. These organisms have evolved to form groups of Protozoa.
Furthermore, there is a change from single-celled animals into many-celled animal. Alleged that multicellular animals first spherical hollow, and consists of a single layer of cells. Based on the hypothesis of this animal called blastea. Blastea name is taken from the form in embryonic development, the blastula.
Algae and Protozoa that exist today is the result of the first radiation, while blastea no longer found except in the form of blastula in embryonic development of multicellular animals. Blastela shape allows it to grow further in the second and third radiation.
Based on thye food, animals can be grouped into: