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Animals... must have a solid structure to support their bodies... soft invertebrate animals

We mentioned in the previous word about animals with vertebrae
We didn't mention it.

We mentioned the bones in it, and that in humans and non-humans they form a skeleton that supports the animal’s body.

The structure is therefore a burden.
The skeleton is connected to its bones by muscles, making these bones levers that move, like the arm, and with the arm is a hand. It is also made of bones, on which muscles are based, which move it. A person can do whatever actions he wants with them and hold on to them whatever he wants. The things . The directions of these movements are increased by the various joints between the bones, some of which are wider in scope than others.

The skeleton, in vertebrate animals and humans, contains visible muscles and internal bones. It is a structure that scientists call the internal skeleton. However, it must... We should not forget that the skull is a bone with the inside of the brain visible. It is not for movement, but rather to protect the brain from harm. The vertebral column itself, which is made of bone, runs through its interior the spinal cord, which is made of nerve. It protects him from harm.

The human skeleton is therefore an internal, internal skeleton, but some of it is external.

- Structures in invertebrate animals

If we move away from vertebrate animals to non-vertebrate animals, we go down the ladder of animals to animals that are the lowest in structure, and therefore they have the lowest life goals, and the lowest fulfillment of life goals. At the same time, we descended from the complex animal (and complexity is only an increase in the art of life, in the technique of life, and in the specialization of work and functions) to the simpler animal.

Here the external structures abound in great numbers, sizes,
And forms, and goals, and let us give examples.

- Soft invertebrate animals

Non-vertebrate animals consist of many phyla. Let us take as our first example the phylum called Mollusks, meaning soft animals, and softness here is the softness of bodies. Who is more deserving of a soft-bodied body than an external structure that protects it?

This phylum consists of several classes of animals
The most important vertebrates are three classes:

The group of animals called Gastropoda, and we represent them by the famous shell animal known as the snail or slug.

The group of animals called bivalves is Pelecypods, and we represent them by the famous animals known as oysters.

Then the third group is called cephalopod
Cephalopods, and we represent them by the famous animal known as the octopus, or the other known as the squid.

Before we describe the snail, the oyster, the octopus, and the squid, or both of them together, and mention where the exoskeleton is located separately, we say that these soft animals contain almost all the organic systems, such as the digestive system, the circulatory system, along with the heart or what takes its place, and the respiratory system. The excretory system, along with the kidneys, the nervous system, along with the developing eye that sometimes sees, as well as the muscular system and the reproductive system.

- Snail or slug

It is an animal crawling very slowly on the ground, with that muscle that resembles a tongue and is therefore known as a foot, with which it emerges from its bony box, carrying this box. This exoskeleton, on top of its back. If he is afraid of something, he will quickly enter his box and disappear completely. Even when he was reassured, he went back out and crawled to ask for his food.

This foot, which walks, has the head of a slug on it, and it is in front of it, and this foot carries within it the stomach, and for this reason the animal is called gastropod.

The snail's intestines twist into this structure and fold. One on top of the other, until it moves to a position above the mouth. The reason is clear. The two exits, from the mouth of Wast, must be at the exit, which is a box with one opening.

(soft-bodied animals of gastropods)