Generally it is a multicellular organism with an athletic capability and a sense, and it is organism with a nucleus at the same time.
There is it for a long time, and, as for the taxonomy to divide a creature into two to an animal and plant, Aristotle tries these two classifications by sense and having athletic capability or not.
But I seem to have admitted that there was the middle creature.
Biologist Linnaeus (Carous Linnaeus, 1702) of the 18th century - ) did a creature with the plant kingdom which I did not have a sense toward and a sense and locomotiveness in the animal kingdom that was a heterotrophy mark for two minutes in 1778.
Materia medica I collected the many things which were able to include an inanimate object as soil, grass, an insect, a fish, a beast equally in Japan before the Meiji era, and to edit was the mainstream, and there was not the concept called the animal.
The classifications to do biology to an animal and plant for two minutes spread since study of Europe flowed in.
Under 2 world theory, I placed a protozoan with the animal of the single cell other than each following crowd in an animal.
The taxonomy how general, and is various is suggested to classifying creatures only with an animal or a plant by the present by biological progress (reference)： Classification) of the creature.
There are many creatures classified in neither an animal nor a plant, and there are a eubacterium, old bacteria, a protist, fungi if I obey them, and the animal kingdom is considered to be one of such a many systems.
The frame was reviewed in the flows such as the molecular genetics of the end many times in the 20th century, and plant kingdom and the bacteria world were big, and the constitution changed.
About the animal kingdom, it is recognized that such a many systems mingled as for the protozoan.
About the Metazoa, I hardly took a change.
It is the degree that considered to be the one of the protozoans till then came to be included in here for a big change.