Animal

Animals

Bread troglodytes, chimpanzee

Dominion:	Eukarya
Kingdom:	Animalia

Edges

It see the text.

In the scientific classification of the alive beings animal is called to each one of the members of a group of eucariontes, pluricellular and heterótrofos (Kingdom Animalia or Animalionte) closely become related with fungi and plants. In order to assign a species to the kingdom Animalia, like for any other group, it is necessary to be based on data, generally genetic or cytological (cellular), that demonstrate the evolutionary kinship with the rest of the members.

Mobility is the most showy characteristic of the members of the kingdom Animalia, but she is not exclusive of the group, which gives rise to that organisms are designated often like certain animals that belong to the kingdom (To see protozoo).

Many people continue using animal opposing it to the term human, but it is had to consider that from a point of view the human being is one more a species of the kingdom Animalia.

1 Structure
2 Reproduction and development
3 Origin and fossil documentation
4 Filogenético tree
5 Edges
6 It also see

Structure

In the following scheme, the common characteristics are all the animals:

Cellular organization: Eucarionte and pluricellular.
Nutrition: Heterótrofa by ingestion.
Metabolism: Aerobe (they consume oxygen).
Reproduction: Sexual, with and zigotos (haplo-diploide cycle).
Development: By means of an embryo.
Type of life: Pluricellular, with weaves and normally movable.
Structure and functions: Cellular weaves very differentiated. Without cellular wall. Some, with quitina. Fagocitosis, in basal forms. Ingestion with fagocitosis later or absorption in derived forms ("more evolved")...

With few exceptions, more remarkable in sponges (edge Porifera), the animals have bodies differentiated in separated. These include muscles, that they can be contracted to control the movement, and , that sends and processes signals. Usually there is also an internal digestive camera, with one or two openings. The animals with this type of organization are known like metazoos or eumetazoos when the first term is used to denominate the animals in general.

All the animals have cells eucariontes, surrounded by one extracellular matrix characteristic composed of colágeno and glycoproteins elastic. This one must to calcify itself in order to form structures like shells, bones and espículas. During the development it forms a relatively flexible frame by which the cells can be moved and be reorganized, making possible structures more complex. This contrasts with other multicellular organisms like plants and fungi, whose cells remain the site by means of cellular walls, that develops a progressive growth.

Reproduction and development

Almost all the animals experience some type of sexual reproduction. The adults are diploides or occasionally poliploides. They have a few specialized reproductive cells that by means of meiosis they produce ova or spermatozoa. These are based to form zygote that it is developed in new individuals.

Many animals can to reproduce asexualmente. This takes place through partenogénesis for example, where they take place eggs without mating, or in some cases, by means of fragmentation.

zygote it is developed initially in a hollow sphere, call blastula, that experiences a reordering and a differentiation. In sponges, the blastula nothing to a new place and is developed in a new sponge. In other many groups, the blastula undergoes a complex reordering much more. First invagina one to form one gástrula with a digestive camera and two separated embryonic leaves: ectoderm external and endoderm internal. In many cases also it is developed mesoderm between both. These embryonic layers are different then to form and organs.

Origin and fossil documentation

It is considered generally that the animals have evolved of protozoos flagellated. Their nearer alive relatives are coanoflagelados, flagellated with the same structure that certain type of cells of sponges. Molecular studies locate them in the supergroup of opistocontos, that also it includes to fungi and to small parasitic become related with these last ones. The name comes from the back location of flagellum in the movable cells, like in many spermatozoa animals, whereas others eucariontes tend to have front flagella (acrocontos).

First of vixens that could represent animals appear towards the end of Precámbrico, it does around 6000000 million years, and it is known them like vendobiontes. Nevertheless, they are very difficult to relate to later fossils. Some of these organisms could be the precursors of the modern edges, but also they could be separated groups, and is possible that they were not really animals in strict sense. Aside from them, many edges known animals made a more or less simultaneous appearance during the period Cámbrico, it does near 570 million years. Still dicute if this event, call cámbrica explosion, it represents a fast divergence between different groups or a change from conditions that facilitated the fosilización, although the comparison of the genes of the groups animals favors to the first idea.

Filogenético tree

  ,___________________________________________________ Choanoflagellata
  |
__|,_________________________________ Porifera
  | |
  | _ _ _ Metazoa _____|,_____________________________ Placozoa
                    | |
                    |___|,_________ Cnidaria
                        | |            
                        | _ _ _ Eumetazoa _____|_________ Ctenophora
                                            | 
                                            |_________ Bilateria