Rosmana A.P | Science | Scientific Facts

Animal is a multicellular eukariotic and heterotroph organism. This organism doesn't have a kind of cellular walls like the plant's and fungi's. Animal is different because they've two kinds of system that responsible for impulse transmittion and movement: nerves system and muscles that is the uniqueness of animal.

Beside that, the others characteristics that come from the animal's life histories have made the animals different. Almost all of the animals have a sexual reproduction system as the dominant reproduction system in their life cycle. Almost all of the animal's species have a little flagellate sperm that will fertilize the ovum cell that bigger than itself and form a diploid zygote that will cleavage through a mitosis proccess that will transform the zygote into two cells, then four cells, then eight cells until it transform into blastule, and gastrule.

Many scientists agree to classified the animals kingdom as a monophyletic creature. Monophyletic means if we can track down all of the animal's descendants line, animals will integrate at one ancesstor. This animal ancestor is estimated as a flagellate protiste that form a colony that live around 700 million years ago in The Cambrian Era.

One of the hypothesis about the origin of animal said that this animal ancestor is formed a ball with a big hole in it. Then, this ball experienced a specialization on it's cells. After that, this organism's cell surface form a fold that folded into it's inner part and finally become an organism called "Protoanimal" that has an appearance look like gastrule in the embrio development stage. But, no evidence cen be found until now.