According to the degree of present complexity in
the alive beings, the animals can classify themselves in different
groups. In an ample group in the most primitive animals consider
themselves included, which are unicellular and make all their vital
functions with a single cell, existing within this cell a certain
division of work; and we were with multicellular organisms in which
the vital functions are going to be made by specialized cells. To
greater specialization of the cells greater degree of complexity
of the organism and also supposes that the cell is going to have
a form and a structure that make it more apt to make the suitable
function. In agreement with the different levels from association
and cellular specialization a series of levels is recognized that
are useful to make a classification of the animals.
Protoplasmatic , protozoa , unicellular organisms
Cellular, the sponges would enter here; the organisms
of this level are formed by associations of independent cells. They
can appear in some cells a certain division of work. The specialized
cells have little tendency to form layers, is to say do not form
Tissue, jellyfish. They have grouped cells forming
a weave species. The nervous network is formed by a set of interconnected
cells and specialized to transmit the impulses, it is spoken of
Organic, the flatworms, these have many weave classes
and some of these weaves are grouped in organs (gonads)
Level of system of organs, superior animals that
besides to have weaves, have them grouped in organs and these in
systems. These systems can present greater or smaller complexity
and some of them serve us to classify.
STANDARDS OF GENERAL MORPHOLOGY
Morphologic standards exist that condition the
external appearance of the animal. The number of them is limited.
These patterns consider the symmetry of the animal, the form of
the head as well as the form of segmentation throughout the body,
of equal way consider as the cavities of the body form.
It exists in most of animals one or several planes
of symmetry that divide to the animal in equal parts, others by
their irregular form do not present it (amoeba). Some protozoa as
well as young the superior animal eggs and embryos are going to
present specific symmetry, is to say gives rise that the planes
that happen through the center divide to the animal in equal parts.
Other more complex animals like hidras, sponges, jellyfish present
broadcast symmetry. Form of cylinder squashed with a certain number
of antimer denominated equivalent parts that leave a central axis.
Superior in that it is observed the mouth denominates inferior buccal
surface and or the aboral one. The superior animals present bilateral
Another characteristic is the cavities of the body,
are animals that do not have cavities and they are not denominated
either coelome present mesoderm, others present/display false cavities,
false coelome, is to say the cavities do not form from a mesoderm
the pseudocoelome animals. Finally the coelome ones are those that
have true coelome produced from the mesoderm.
There are animals that present the body segmented
in metamere (earthworm); others like the insects, arthropoda have
the segmented body existing clear differentiation of the segmented
ones. In the vertebrates the metamere is evident in the embryonic
stages and tends to disappear in the adults.