Water and ammonia leaves through these pores. Aerobic respiration produces carbon dioxide as a waste product. This is released from the planarian by diffusion. To carry out aerobic respiration, the planarian must get oxygen to the cells of its body. Oxygen enters the planarian by diffusion. The special features of the Phylum Platyhelminthes includes the protonephridia.
These structures can be considered primitive kidneys. They are unique to the phylum. Planarians are placed in the Class Turbellaria, and these were discussed extensively above. The flukes Class Trematoda are mostly parasites of vertebrate animals those with backbones.
The animals generally have a sucker around the mouth and one on the ventral surface. These suckers allow the animal to cling to the body organs in which they live. The adult flukes live in hollow organs like the heart, tongue, kidney, and gall bladder on lower surface of the liver. Many flukes have immature stages that live in other animals.
For example, immature stages larvae of the human liver fluke live in snails. These are released from snails, and a second immature stage then lives within fish. When humans ingest raw or undercooked fish, they also ingest immature stages of the fluke. The immature stages migrate to the bile ducts of the liver where they mature.
The mature stages may live within the bile ducts for years. While there they cause damage of the liver and may cause death of the human host. Eggs are produced by the adult within the bile ducts. The eggs travel through the bile ducts to the digestive tract and pass out of the host in feces. The eggs are ingested by snails, and the cycle is repeated. Humans can also become infected with a human blood fluke. Immature stages of this fluke also live within snails. These larvae leave the snail and are present on the ground in areas of poor sanitation.
The immature stages enter humans by burrowing through the skin of a human host. The immature flukes enter blood vessels and mature there.
They can cause anemia and damage to the liver, bladder, and brain. Tapeworms Class Cestoda are also parasite flatworms. Humans can become infected with tapeworms by ingesting uncooked or undercooked pork or beef. Larval immature stages of the tapeworm present in the muscle of pigs or cows are ingested. The tapeworm attaches to the intestine while passing through the digestive tract using hooks or suckers.
The tapeworm matures and grows in the intestine, a food-rich environment. The tapeworm grows longer by budding. Each proglottid contains reproductive structures and eggs are produced and become fertilized within each segment. The oldest proglottids break off of the tapeworm and leave the host with feces. In areas of poor sanitation, pigs or cows ingest the zygotes. The immature stages burrow into the muscle tissue of the pig or cow and the cycle repeats. The impact the Phylum Platyhelminthes has on humans is the fact that several animals within the phylum are human parasites.
The Phylum Nematoda roundworms or nematodes includes harmless, soil-dwelling roundworms nematodes that eat decaying organic material or small soil animals. The phylum also includes plant parasites that infect the roots of plants. These parasitic nematodes decrease the productivity of many human crops. The eye spots are sensitive to light. Planarians move away from the light and are most active in the dark. Second, light and water current can be used demonstrate kinesis change of speed and taxis change of direction.
Planarians are also sensitive to shock. Therefore, planarians can be conditioned with several stimuli and responses. Planarians have a head region with sense organs. The nervous system of Dugesia is somewhat more complex than the nerve net of Cnidarians. It consists of a brain and nerve cords arranged in a ladder-like configuration. Planarians have ocelli eyespots allow the presence and intensity of light to be determined. These structures are covered but have an opening to one side and forward.
They can tell the direction of light because shadows fall on some of the receptor cells while others are illuminated. They move away from light. Planarians are hermaphroditic , that is, they contain both male and female sex organs. They can reproduce asexually simply by pinching in half; each half grows a new half.
The reproductive cycle typically involves two host species, a primary host and a secondary or intermediate host. Adults live in the primary host and larvae develop in the secondary host. The life cycle often alternates between sexual and asexual reproduction. Nearly half of people in the tropics have blood flukes. Schistosomiasis is a blood fluke that afflicts million people in the world.
The secondary host is a snail. Figure 1. Left: Planarian anterior end X Middle: Planarian digestive tract mid section X Right: Planarian c. Observe either a preserved liver fluke or a slide of a liver fluke using a dissecting microscope.
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