9.3.3 Phylum Platyhelminthes (Gk. Platy: flat, helminth: worm)
Platyhelminthes are also called flatworms or acoelomate worms. The characteristics of phylum Platyhelminthes are:
Habit and Habitat:
Platyhelminthes are either free-living (e.g., planaria) or parasitic (e.g., tapeworm). These worms are recorded both in fresh water and marine, while parasitic worms are also found in the liver and gut of human beings.
Body:
Flatworms are triploblastic, bilaterally symmetrical, and soft-bodied animals. Their body is dorsoventrally flattened and acoelomate. Free-living forms possess
incomplete digestive systems i.e., with a single opening known as a mouth while less developed or absent in parasitic forms. The excretory system is well well-developed protonephiridial system containing flame cells. The nervous system consists of a network of nerves, with two longitudinal nerves and an anterior cerebral ganglion. Locomotion occurs utilizing underside cilia.
Reproductive system:
Asexual by fission (regeneration) sexual reproduction is also present. These worms are bisexual with well-developed gonads, ducts,, and accessory organs, fertilization is internal, and development may be direct or indirect. Examples: Planaria (Dugesia), liver fluke (Fasciolla), and Tapeworm (Taenia).
Evolutionary Adaptation in Platyhelminthes:
There is a simple gastrovascular type of incomplete digestive system. Respiratory and transport systems still do not appear, it occurs by diffusion. Excretory organs appeared, called the protonephridial system. The initiation of a centralized nervous system with two longitudinal nerves and cerebral ganglion. The parasitic form developed many parasitic adaptations to adjust themselves in parasitic life.
Importance of Platyhelminthes:
The parasitic flatworms cause many serious diseases. In humans, such as liver fluke infect the liver, tapeworms to the human intestine, and blood fluke in cattle, etc.
Phylum Aschelminthes
(Greek: Askos means Sac, Helminths means worms) Nematodes or roundworms
Habit:
Mostly parasitic, some are free living.
Habitat:
Muscular and intestinal parasites of humans and other animals, some are free-living (in soil, roots of plants).
Body:
Triploblastic and bilaterally symmetrical. Segmentation is absent, the body is cylindrical and pointed at both ends. The body cavity is psuedocoel, which is a remnant of blastocoel (not formed by mesoderm).
Digestive system:
It is complete and consists of a single tube with a mouth at the anterior end and an anus at the posterior end. Muscular layer: It is not continuous: divided into four longitudinal quadrants, (two dorsolateral and two ventrolateral). the nervous system consists of a nerve ring from which nerve cords and fibers extend in various directions.
Senses:
Sensory papillae are present in the front part of the body, especially on the lips. Sexes are mostly separated. Dioecious some are monoecious, and fertilization is internal. Circulatory and respiratory systems are absent. Intestine Anas duct Vaiva
Size:
varies from microscopic to large such as Ascaris, more than one foot in length. Examples: among parasites are Ascaris, pinworm and guinea worm, Caenorhabditis (free living), etc.
Evolutionary adaptation in Aschelminthes:
These worms have adapted themselves in almost all types of habitats. This is the first phylum in which a complete digestive system appeared, beginning from the mouth and ending at the anus. The circulatory and respiratory organs still have not appeared, however, the excretory system consists of canals and ser et and other protonephridia. The nervous system is also better developed than Platyhelminthes and possesses a pharyngeal ring and many nerves.
Importance of Nematodes:
Aschelminthes (nematodes) are the cause of many serious parasitic diseases, such as: 1. Ascaris lumbricoides is a human intestinal parasite that causes anemia, abdominal pain, fever, it also migrates to the lungs and causes cough and other complications.
Rhabditis:
Many species of this genus live in soil, organic matter, water, and feces of many animals.
3. Enterobius vermicularis (pinworm):
It is found all over the world, especially in Europe, America lives in the caecum, appendix, and colon of man, causing itching of the anus, and inflammation of the colon and appendix, resulting in insomnia and loss of appetite.
Hookworms:
(Acyclostoma duodenal) it is also a parasite of the human intestine and causes bleeding. Free roundworm: in the soil causes the disease in potatoes, onions, cotton, apples, etc.
0 Comments