Introduzione
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Bibliography:
"Invertebrate Digestive Systems - Boundless Open Textbook." Boundless. Web. 17 Dec. 2014. <https://www.boundless.com/biology/textbooks/boundless-biology-textbook/animal-nutrition-and-the-digestive-system-34/digestive-systems-195/invertebrate-digestive-systems-747-11980/>.
"Mollusca." Digestive System. Web. 17 Dec. 2014. <http://digestiveproject.weebly.com/mollusca.html>.
"The Digestive System and Its Arthropoda Phylum." Digestive System. Web. 17 Dec. 2014.
Miller, Kenneth, and Joseph Levine. "Arthropods." Biology. Fifth ed. Upper Saddle River, New Jersey: Prentice Hall, 2000. 618. Print.
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Digestive glands are located in the arms of the sea star.
Solid wastes are released through the anus in the form of feces. However Brittle stars which lack an anus will release their undigested materials through the mouth.
Starfish have the ability to flip its stomach to pour out enzymes and then digest their prey in the prey's own shell.
Digestive systems vary greatly in this phylum.
In spiders, some pump digestive enzymes from the gut to the prey and then suck the liquified tissues of the prey. Other spiders will grind the prey up using their chelicera.
For the most part, digestion in insects is helped with the insect's saliva that includes digestive enzymes which help break down food.
The stomach in a spider sends the food deeper into its digestive system.
In the spider's mid gut, nutrients are extracted from the food.
Finally spiders use malpighian tubules to extract wastes to be expelled through the anus.
Most mollusks have a radula which is a structure of tiny teeth which is used for scraping food particles into the mouth.
The mollusks that don't have radula use their gills to get the food from water into their mouths.
Afterwards, the food then goes to the digestive glands and then to the intestine.
Undigested food becomes solid waste that leaves through the anus in the form of feces.
Annelids have a digestive tract (gut). This is a long tube within the body cavity of the worm and extends from the mouth to the anus (tip of the tail).
Carnivorous annelids have a pharynx with two or more jaws attached to it.
In detritus feeders, the pharynx is covered with a sticky mucus. This causes food particles to stick to this mucus.
When the pharynx returns to its normal position, it carries food particles into the gut where the food is digested.
Parasitic annelids such as leeches suck blood and tissue fluids from their host.
To catch their prey, nematocysts are used to stun or kill. After wards, the tentacles are used to push food into the mouth into the gastrovascular cavity, where the food is gradually broken up into tiny pieces. Then, these food fragments are taken up by special cells in the gastroderm that digest them further. Furthermore, the nutrients are then transported throughout the body by diffusion. Since cnidarians do not have anuses, materials which cannot be digested are sent out of the mouth after a few hours.
All roundworms have a long tube-shaped digestive tract with openings of both ends. Food enters the mouth and then goes straight into the digestive tract. Finally, materials that cannot be digested leaves through the anus.
This is a jellyfish.
Phylum Porifera:
Sponges have nothing which resembles a mouth nor a gut. They are filter feeders, which means they sift microscopic particles of food from the water that passes through them. These food particles stick to the sponge's collar cells and these cells engulf the food. If the collar cells do not digest the food, then the amebocytes are presented with the food. Finally when amebocytes are finished digesting the particles, they move around and deliver digested food to other parts of the sponge.
Tapeworms on the other hand, that live in the host's intestines do not have digestive tracts. They suck food that passes by using their hooks or suckers.
This is a flatworm.
Free-living flatworms have gastrovascular cavity with one opening at the end of a muscular tube called a pharynx. The pharynx is used to suck food into the gastrovascular cavity. Also, the grastrovascular cavity forms an intestine with many branches. Moreover, digestion is completed inside the cells of the intestinal wall. These branches are found in most parts of the body. This allows completely digested food to diffuse to other body tissues. Similar to cnidarians, undigested materials are expelled through the mouth.
Parasitic flatworms have a pharynx which pumps food into a pair of dead-end intestinal sacs. Food is digested inside these sacs. These flatworms normally feed on blood, tissue fluids, or pieces of cells.