Unlike the human digestion system, crayfish have a rather simple system. Starting with the mouth, food is ingested and passed into the cardiac stomach via the esophagus. In this first stomach food is stored until it is passed into the pyloric stomach; filled with small “teeth” like structures. Once ground the food is handed out to the intestine, where nutrient is absorbed into the blood vessels and taken around the body. After the intestine, the excess waste is removed through the anus.
The digestion tract for earthworms is much like the crayfish. Food enters the mouth and gets pushed down into the esophagus by the pharynx. Next in line is the crop; an organ very similar the cardiac stomach. In the crop food in held until it is moved into
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As water moves through the gills oxygen gas is picked up and taken in by the blood vessels. The water is moved upward, forward, and out of the crayfish through the mouth. With the current of the blood, the oxygen is taken towards the tail and up towards the heart. By the time the oxygen gas has reached the heart most of it has become poorly oxygenated. The heart continues pumping ad when passed by the green glands any material not needed is excreted. As the blood arrives back at the gills, the now carbon dioxide gas is removed and more oxygen is taken in.
Earthworms, on the other hand, have a much simpler way of getting things done. Although living without any lungs or gills seems impossible, the earthworm is living proof that it is. If their skin is moist and coated with mucus, diffusion will occur. To get oxygen into its body it defuses into the worm; almost like the oxygen is being pulled into it. From there blood vessels grab the oxygen gas while being circulated by the pumping of its hearts. Soon after, the oxygen is used up and becomes carbon dioxide gas. The gas then defuses, or gets pushed, out of the worm; making room for more