Phylum Nematoda:

Nematodes (Gr. nematos, thread) or roundworm are among the most common animals on on the earth-some 5 billion may be in one acre.

Nematode is a diverse group of elongated, unsegmented worms that belong to the phylum Nematoda. They are found in almost every habitat on Earth, including soil, water, and the bodies of plants and animals.

There are over 20,000 species of nematodes, with varying sizes ranging from microscopic to several meters in length. Some nematodes are parasitic, causing diseases in humans, animals, and plants, while others are free-living and play important roles in ecosystem processes such as nutrient cycling and decomposition.

Despite their small size and simple body structure, nematodes have a complex biology and have been the subject of extensive research in fields such as agriculture, ecology, and medicine. They are also commonly used as model organisms in genetic and developmental studies due to their rapid reproduction and transparent body structure.

• Classification:

This phylum includes over 20,000 described species, with new species being discovered all the time. Nematodes are divided into two major classes: Adenophorea and Secernentea.

• Class Adenophorea:

The class Adenophorea is a relatively small group of nematodes that are characterized by the presence of a glandular pharynx, which is used for feeding. They are further divided into two subclasses: the Enoplia and the Chromadorea.

Subclass Enoplia:

The Enoplia are a small group of nematodes that have a characteristic conical head with a single median amphid, which is a sensory organ used for chemoreception. They also have a rigid cuticle and are primarily found in soil and freshwater habitats.

Subclass Chromadorea:

The Chromadorea are a larger and more diverse group of nematodes that have a wide range of lifestyles and ecological roles. They have a more flexible cuticle than the Enoplia and typically have two amphids on their head. The Chromadorea are further divided into several orders, including the Rhabditida, the Spirurida, and the Oxyurida.

• Class Secernentea:

The class Secernentea is a larger and more diverse group of nematodes that are characterized by the presence of a secretory gland in their pharynx. They are also known as the "secretory" nematodes. This class is further divided into several subclasses, including the Diplogasteria, the Tylenchia, the Ascaridia, and the Spiruria.

Subclass Diplogasteria:

The Diplogasteria are a small group of nematodes that are primarily found in soil and leaf litter. They are characterized by their diplogasteroid reproduction, which involves the production of two embryos at a time.

Subclass Tylenchia:

The Tylenchia are a large and diverse group of nematodes that have a wide range of lifestyles and ecological roles. They include both plant parasites and free-living nematodes, and are further divided into several orders, including the Tylenchida, the Dorylaimida, and the Triplonchida.

Subclass Ascaridia:

The Ascaridia are a group of nematodes that are primarily parasites of vertebrates, including humans, livestock, and wildlife. They include important human pathogens such as Ascaris lumbricoides, which causes intestinal infections.

Subclass Spiruria:

The Spiruria is a large and diverse group of nematodes that are primarily parasites of animals. They include several important human pathogens such as Wuchereria bancrofti, which causes lymphatic filariasis, and Onchocerca volvulus, which causes river blindness.

Characteristics of Phylum Nematoda:

Some of the key characteristics of nematodes include:

• Body shape:

Nematodes have a long, cylindrical body shape that is tapered at both ends.They are triploblastic, bilateral and pseudocoelomate.

• Cuticle:

They have a tough, protective outer layer called the cuticle that is secreted by the underlying epidermis. The cuticle provides protection against environmental stressors and also helps to maintain the worm's shape.

Layers of Nematode's cuticle

• Digestive system:

Nematodes have a complete digestive system with a mouth, pharynx, intestine, and anus. The pharynx is typically muscular and can be used to suck in food or penetrate host tissues in parasitic species.

• Reproduction:

Most nematodes have separate sexes, although some species are hermaphroditic. Nematodes typically reproduce sexually, but some species are capable of asexual reproduction as well.

• Sensory structures:

Nematodes have a range of sensory structures, including chemosensory organs on the head called amphids and phasmids on the tail. Some species also have specialized sensory structures such as papillae, sensilla, and cilia.

• Locomotion:

Nematodes move using a unique style of locomotion called undulatory movement. They use contraction of longitudinal muscles to generate a wave-like motion that propels them forward.

• Ecological roles:

Nematodes have a wide range of ecological roles. Some species are free-living and play important roles in nutrient cycling and soil ecology, while others are parasites of plants, animals, and humans.

• Feeding and Digestion:

Nematodes have a complete digestive system with a mouth, pharynx, intestine, and anus. They feed on a variety of organic matter, including bacteria, fungi, algae, and small animals such as other nematodes. Some species are also parasites that feed on the tissues or fluids of their hosts.

The mouth of nematodes is typically surrounded by sensory structures called amphids, which are used to detect chemical signals in their environment. The pharynx is a muscular tube that extends from the mouth and is used to draw in food. Some nematodes have a specialized pharynx called a stiletto, which is used to pierce the tissues of their host.

Once the food is ingested, it is passed into the intestine for digestion and absorption. The intestine is lined with specialized cells that secrete digestive enzymes to break down the food. The nutrients are then absorbed across the intestine wall and transported to the rest of the body.

Waste products and undigested materials are eliminated through the anus, which is located at the end of the body. Nematodes also have specialized excretory structures called excretory canals, which help to regulate the balance of water and solutes in their body.

Inshort, the feeding and digestion process in nematodes is similar to that of other animals with a complete digestive system. However, nematodes have evolved a variety of adaptations to help them feed on their diverse range of food sources, from specialized pharynxes for piercing host tissues to specialized enzymes for breaking down tough plant material.

• Other body System:

As with all living organisms, nematodes must maintain a proper balance of water and solutes within their bodies, a process known as osmoregulation. They also need to eliminate metabolic waste products, a process known as excretion. Here's a brief overview of osmoregulation and excretion and respiratory system in Phylum Nematoda:

• Osmoregulation:

Nematodes have a simple body plan, with a longitudinal muscle layer and a pseudocoelom that functions as a hydrostatic skeleton. The pseudocoelom is filled with a fluid called pseudocoelomic fluid, which serves as the main extracellular fluid in nematodes. The concentration of solutes in this fluid must be carefully regulated to maintain the proper osmotic balance with the environment.

In free-living nematodes, osmoregulation occurs primarily through the diffusion of water and solutes across the body wall. The cuticle, a tough outer layer that covers the body, helps to prevent excessive water loss. In parasitic nematodes, osmoregulation is more complex due to the host-parasite relationship. Parasitic nematodes have evolved a variety of adaptations to help them survive in their host's body fluids, including specialized excretory structures and cuticular adaptations.

• Excretory System:

Nematodes excrete waste products through a specialized excretory system composed of a series of canals and excretory pores. The canals, called excretory tubules, are lined with cells that actively transport waste products out of the body fluid and into the tubule lumen. The tubules then empty into a bladder-like structure called the excretory vesicle, which opens to the outside through an excretory pore.

• Respiratory System:

The respiratory system in nematodes is relatively simple and consists of a network of tubes called tracheae. The tracheae are connected to the outside environment through small openings in the cuticle called spiracles. These spiracles allow for gas exchange between the nematode's body and the environment.

In free-living nematodes, the respiratory system is primarily responsible for oxygen uptake and carbon dioxide elimination. However, in parasitic nematodes that live inside their hosts, the respiratory system may be modified or reduced due to the availability of oxygen within the host's body.

• Nervous System:

The nervous system in nematodes is composed of a network of nerves that run the length of the body and form ganglia or nerve cell clusters at specific points. The nervous system is responsible for coordinating the nematode's movements and responses to the environment.

Nematodes have a simple nervous system, with a nerve ring located near the anterior end of the body and a ventral nerve cord that runs along the length of the body. The nerve ring receives sensory input from the environment, while the ventral nerve cord sends motor signals to the muscles to control movement.

Nematodes also have specialized sensory organs, including amphids and phasmids, which are located near the anterior and posterior ends of the body, respectively. These sensory organs help nematodes detect chemical cues in the environment, as well as temperature and other physical stimuli.

• Life Cycle-Reproduction:

The reproductive system of nematodes is relatively simple but highly efficient. Nematodes reproduce sexually, with males and females mating to produce offspring.

• Male reproductive system:

The male reproductive system consists of a testis, vas deferens, and copulatory spicule. Sperm are produced in the testis and then travel through the vas deferens to the copulatory spicule, which is used to transfer sperm to the female during mating.

• Female Reproductive System:

The female reproductive system consists of a paired ovary, oviduct, uterus, and vulva. Eggs are produced in the ovary and then travel through the oviduct to the uterus, where they are fertilized by sperm. The fertilized eggs are then deposited through the vulva into the environment, where they develop into larvae.

The life cycle of nematodes varies depending on the species and the environment. In general, nematodes hatch from eggs as first-stage larvae (L1) and then go through several molts to become second-stage (L2) and third-stage (L3) larvae. These larvae may then undergo a period of dormancy or develop directly into adults.

Once nematodes reach adulthood, they mate and produce eggs, completing the life cycle. Some nematodes have a relatively simple life cycle, while others, such as those that are parasitic, may have more complex life cycles that involve multiple hosts.

Frequently Asked Questions-FAQs

• What is nematoda?

The word "nematoda" is a derived from Greek language meaning "thread".They are among the most common invertebrates in the planet.They can be easily identified from their smooth and tough outer covering

and unsegmented body.

• What is the importance of nematodas?

Nematods have the the ability to enhance the soil fertility, maintain the population of soil organism and help the plants to consume minerals from land.

• Note:

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Phylum Nematoda-Classification, Characteristics & Reproduction