Advantages/Disadvantages

CRAYFISH

ADVANTAGES
Exoskeleton for protection and support. The ligament and muscles attach to the exoskeleton, providing extra support and internal organ and muscle structure. They have a nerve cord located on the ventral side of the body. Compared to the humans, the nerve cord is located on the dorsal side of the body. (The spine.) Being on the ventral side, it is more protected. If anything, the predator will attack the bottom, but ligament-filled pinchers should protect that side of the body. Having gills attached to the Crayfish's legs is an advantage as well. As the crayfish walks, water is constantly being "swished" against the legs. Not causing much energy to breathe.

DISADVANTAGES
The Exoskeleton may hinder movement. Being cold-blooded, this organism has to move to different environments to maintain homeostasis. For example, if the crayfish is cold, it must move to a different environment where it is warmer. Vise-versa, if the crayfish is too cold, it must move to a more "warmer" climate. The crayfish's exoskeleton must molt. Like a snake must replace it's skin. So if the crayfish has just molted out of it's old shell, the crayfish is vulnerable to it's predators due to growing no shell yet. A disadvantage of the gills being attached to the legs, is if any of the legs are torn off, it may decrease the breathing rate. Therefore explains the reason to have multiple legs.

EARTHWORM

ADVANTAGES
Being made up of mostly muscle, the earthworm can easily stretch, contract, and squeeze into spots. For there is no skeletal system; no bones to break! The integumentary system of the earthworm must be moist, so it may be easy, or it may be hard to live around moist or wet climates in order to breathe. The worm may not struggle to find food, for it mainly consumes soil. Therefore, soil is everywhere! This way, the earthworm may not struggle to find food.

DISADVANTAGES
Having no skeletal system, you would have a hard time to lift heavy objects, for there is no bones to support all of that muscle. Another disadvantage, the worm must keep from drying out to breathe. The worm uses diffusion to release carbon dioxide, and take in oxygen. If there is no moisture, the worm will dry out and die.

RAT 
ADVANTAGES
The rat is warm blooded, allowing it to go where it pleases, without having to worry about looking for cold or hot environments to regulate homeostasis. The rat has a four chambered heart. Having a four chambered heart gives the advantage of longer endurance; for there is more oxygen delivered to the muscles.
DISADVANTAGES
Rats are known to have Cardiac failure in their circulatory system. For example, if a rat may be too exited, the circulatory heart may become too tired, and give up. Another disadvantage of the rat includes the risk of getting parasites; due to the fur on the integumentary system. An complex digestive system results in a slow digestion. Most similar to human's digestive system.

FROG
ADVANTAGES
Having a mucus-lined, semi permeable integumentary system, in the water, the frog breathes through it's skin. It's dual respiratory system allows it to leave and enter the water whenever it wants. On the limbs, are webbed feet; assisting in swimming. The integumentary system also allows the organism to live anywhere. From the desert to the top of mountains. Since it is cold-blooded, the frog may sometimes have to burrow underground to maintain homeostasis. Surrounding itself in a cocoon made of it's shed skin. To prevent freezing, it uses glucose to keep internals flowing, as the external body may freeze solid. Much in a "Limbo" state. To get around, frogs may jump or waddle. When jumping, there are solid abdominal muscles to absorb the landing impact. The digestive system includes a variety of insects, snails, and worms. Larger frogs may choose to consume on bigger prey, such as a mouse. (If large enough.) The digestive system contains a pharynx just like the other organisms, a stomach, large and small intestine, and an cloaca.

DISADVANTAGES
The frog does not have a ribcage. Making it somewhat vulnerable to it's internals, but strong abdominals may save the internal organs. Without teeth, a slower complex digestive system may take longer than the other organisms.

*all photos taken by me*