Friday, December 15

Basic Information About Nematoda (Roundworms)

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General Characteristics of Nematoda (Roundworms):

  1. They are elongated, cylindrical form with a definite antero-posterior axis.

  2. Unsegmented with fundamental bilateral symmetry and tri-radiate symmetry in the anterior end.

  3. Roundworms are parasitic and free living creatures.

  4. Larger numbers of helminthes parasites of man.

  5. Nematoda varies in their sizes.

  6. Sexes are separate and generally exhibit considerable sexual dimorphism.

Classification of Nematoda:

  1. Aphasmida – lacking phasmids, caudal chemoreceptor.

  2. Phasmida – with phasmids.

Intergumentary System of Nematoda:

Consist of a non-nucleated cuticula secreted from underlying epithelium, three layers; namely:

  1. Cuticular or hyaline layer

  2. Epithelial or sub-cuticular layer

  3. Dermo-muscular layer

The body cavity is a pseudocoele where all the viscera are suspended.

Digestive System of Nematoda:

The nematodes have a complete digestive tract, extending from mouth to anus, an opening on the ventral surface not far from the posterior extremity.  The anterior segment of the digestive canal is generally a muscular esophagus.

Excretory System of Nematoda:

It consists of two trunks called the collecting tubules or canals, with excretory gland and opening, the excretory pore.

Nervous System of Nematoda:

Consist of a dorsal, a ventral and 4 lateral longitudinal trunks with transverse commissural; the circum-esophageal ring which constitutes the nerve center, terminating a pair of laterally placed minute receptor organs in the cephalic or cervical region of all nematodes.  Phasmids or caudal chemoreceptor organs are a pair of minute post-anal organ in species without caudal glands.

Reproductive System of Nematoda:

The reproductive organs are bilateral, symmetrical; tubular and coiled within the body.

Some female worms can have a single reproductive system and they are in a long tube which is called inside the body.  In other worms, they have a double reproductive system, from vagina, they branched out into 2 uterus, this is in Ascaris, Enterobius, and hookworms, several of females are viviparous and rest are oviparous.

ECG – consists of a multinucleate mass of protoplasm, usually containing yolk granules.  The shell is made up of 3 layers; vitelline membrane, chorionic or true shell and albuminous coverings.

Developmental stages of Nematoda:

Nematodes have 5 successive fundamental stages, 4 larval and the adult stage, with growth and a mouth cuticle between each 2 stages.

Two (2) Types of Life Cycle of Nematoda:

  1. Direct – homogonic, don’t require an intermediate host, from egg, they developed into the infective stage.

  2. Indirect – heterogenic, require 1 or 2 intermediate host for the development into an infective stage.

Manner of Infection of Nematoda:

  1. Ingestion of eggs thru contaminated food or drinks.

  2. Ingestion of the encysted larva.

  3. Through skin penetration by filariform larva.

  4. Thru bite of arthropods or insect vectors as in filarial worms.

  5. Manner of transmission is still unclear.

Modes of Attachment of Nematoda:

  1. Oral attachment by sucking.

  2. By anchorage with their attenuated eggs.

  3. By penetration of tissues.

  4. Retention in the mucosal folds, producing pressure against it.

Means of Nutrition of Nematoda:

  1. Sucking and ingestion of blood.

  2. Ingestion of tissues.

  3. Feeling on intestinal contents.

  4. Ingestion of nourishment from body fluids.


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