The name Nematoda means pointed ends. These animals have an elongated worm-like body with pointed ends. One end of the body is called the anterior end. However, the head is not clearly demarked. There are no special sense organs at this end.
General Characters of Phylum Nematoda
- The nematodes are triploblastic.
- They show bilateral symmetry. Their body is unsegmented.
- They are pseudocoelomate. The body cavity is called pseudocoel. It is derived from the hollow space, the blastocoel. Blastocoel is formed in the blastula stage during embryological development. So their coelom is not formed from mesoderm. Pseudocoel has a large number of vacuolated cells (cells with vacuoles). These cells are filled with a protein-rich fluid. This fluid produces high hydrostatic pressure (pressure due to fluid).
- They have different sizes. Nematoda may be microscopic or some nematodes having up to a one-meter length.
- They have a tube-like digestive system. It is in the form of an alimentary canal with two openings. The mouth is present at the anterior end and the anus is present at the posterior end. A fluid-filled space is present between the body wall and the alimentary canal. So it forms a tube within tube” type structure in nematodes. The digestive system of parasitic forms is simple.
- The excretory system consists of the excretory canal. These canals run longitudinally and unite at the anterior end to form a single canal. This canal opens outside through an excretory pore on the ventral surface.
- There is a nerve ring around the pharynx. It gives rise to dorsal, ventral, and lateral nerve cords. These nerves run throughout the length of the body of the worm. Their sense organs are in the form of the sensory papilla. It is present on the lips at the anterior end.
- These systems are absent in nematodes. The exchange of gases takes place through the general body surface
- Locomotion takes place by muscles. These muscles contract and relax and produce undulating waves. These muscles are arranged in four bands. Two are dorsolateral and two are ventrolateral. The circular muscles are absent. So, they can bend only dorso-ventrally.
- Reproduction: The sexes are separate. The female gonads are ovaries and these produce eggs. The male gonads are testes and these produce sperms. A larval stage is present during its life cycle.
Importance of Phylum Nematoda
Aschelminthes have many important parasites. These bacteria cause some very serious diseases in man and plants.
- Ascaris Lumbericoides: It is an intestinal parasite of man.
- Rhabditis: This genus contains many species. They are found in soil, organic matter, water, and the feces of man and animals.
- Enerobius Vermicularis: It is commonly known as a pinworm. It is present everywhere but it is more common in Europe and America.
Pinworm is a parasite of the human caecum, colon, and appendix (parts of the large intestine). Their movement causes intense itching of the anus. It also causes inflammation of the mucous membranes of the colon and appendix. It results in insomnia and loss of appetite.
- Acyclomstoma duodenale: It is commonly known as hookworm. It is a parasite of the human small intestine. Hookworm is found in Asia, North Africa, and Europe.
It is a very dangerous parasite. Hookworm holds the villi of the intestine and sucks blood and body fluid. It produces an anticoagulant during feeding. This anticoagulant prevents the clotting of blood. It leaves the wound bleeding after feeding. It causes severe anemia in children and retard (stops) physical and mental growth.
Round Worms as Decomposer
Roundworms are present outdoors. They play an important role in the breaking down of organic matter. A single rotting apple may contain 90,000 worms. Billions of worms are present in each acre of topsoil (upper part of the soil).
Other Related Phyla:
- Phylum Porifera Characteristics & Examples
- Phylum Chordata Characteristics & Classification
- Characteristics of Phylum Echinodermata
- Phylum Mollusca Characteristics and Examples
- Phylum Arthropoda Characteristics and Examples
- Phylum Annelida Characteristics and Examples
- Phylum Platyhelminthes Characteristics and Examples
- Phylum Coelenterata/Cnidaria Characteristics and Examples
- Phylum Porifera/Sponges With Examples & Characteristics
- Phylum Protozoa: Characteristics & Groups/Classes