Muscular System

The muscular system is an organ system that allows the body's movement and helps regulate the blood throughout the body. There are three kinds of muscles, the skeletal muscles, cardiac muscles, and the smooth muscles. Muscles in the organisms body usually provide balance, movement, strength, posture, and heat for the body to be warm.

Earthworm

The earthworm has two sets of strong muscles that help them move; the longitudinal and circular. When longitudinal muscles contract the worm's body will become shorter. When the circular muscles contract the body of the worm will become thinner. When the segments of the worm contract and relax, the notion of the longitudinal and circular movement is shown. The muscular system also help the worm defend its self and helps it move around. Earthworm does not have limbs so it has setae, hair like structures that allows the organism to grasp the soil to help move its self. 
Crayfish

The crayfish has powerful abdominal muscles to help them swim backwards and also in their tail because they swim a lot. There is also muscles on the pincers, walking legs, mandibles, and stomach. The claws are full of muscles so when it is protecting its self it can do serious damage to the other organism. 

Grass Frog 

The muscles of the frogs' legs enable hem to jump pretty far. They also have muscles in their stomach because every time they jump, sometimes they would not land on their hind legs, instead on their stomach. The frog has muscles on the arms but because they do not use them a lot there is only a little bit of muscle. the jaw is also filled with muscles because the frog has to eat its prey alive, so the muscles can help prevent the prey for getting away. 

White Rat 

 

The rat has strong muscles in their short and tiny legs because it uses them a lot, like to run after their prey or to climb up a tree. The mouth of the rat is really small so it would be constantly chewing on something, which has a lot of muscles to help. Sometimes the rat uses their short hand to help them eat food.