Long muscles lie just underneath the epidermis. Planarians have no apparent circulatory or respiratory systems; however, they do possess muscles which line the inner wall of the body in longitudinal, diagonal, and circular orientations. The mesenchyme of the planarian body is populated with numerous undifferentiated pluripotent cells, known as neoblasts.
Planarian, class Turbellaria , any of a group of widely distributed, mostly free-living flatworms of the class Turbellaria phylum Platyhelminthes. Planaria is the name of one genus, but the name planarian is used to designate any member of the family Planariidae and related families. Planaria are common to many parts of the world, living in both saltwater and freshwater ponds and rivers. Some species are terrestrial and are found under logs, in or on the soil, and on plants in humid areas.
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 phylum includes several human parasites see below. Like the Phylum Platyhelminthes, the Phylum Nematoda consists of bilaterally symmetrical animals that have the organ system level of organization.
The Phylum Nematoda differs from the Phylum Platyhelminthes in two significant ways. First, roundworms have a complete digestive system. This means that there are two opening to the digestive system.
The mouth at the anterior ingests or swallows food, and the anus at the posterior releases digestive waste. A complete digestive system is much more efficient than a cul-de-sac gut. The complete digestive system allows continuous processing of food. A roundworm can eat continuously, food digestion can occur continuously, and waste material can be released continuously. Animals with a cul-de-sac gut must wait until a meal has been digested, release digestive waste from the mouth, and only then swallow the next meal.
The second significant difference between the Phylum Nematoda and the Phylum Platyhelminthes is that the roundworms have a fluid filled body cavity.
The presence of this structure allows space and cushioning for organs, provides the roundworm with a hydraulic skeleton, and aids in the distribution of food from the digestive tract to the other cells of the worm.
Several human parasites are roundworms. Many people in tropical countries are infected with hookworm. Immature stages of this parasitic worm burrow through the skin, travel through the blood vessels to the lungs, enter the air spaces of the lungs and crawl into the esophagus. The immature stage is then swallowed. The worm attaches to the intestine with hooks and matures into an adult.
Fertilized eggs are released with feces, and the zygotes develop into immature stages on soil. When people walk barefoot over the soil, they become infected.
The mature hookworm drinks blood and lymph juices. They cause anemia due to blood loss. The human roundworm is common where human feces is used as plant fertilizer. People ingest eggs when they eat plant material.
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