General Characteristics of Nematoda (Roundworms):
- They are elongated, cylindrical form with a definite antero-posterior axis.
- Unsegmented with fundamental bilateral symmetry and tri-radiate symmetry in the anterior end.
- Roundworms are parasitic and free living creatures.
- Larger numbers of helminthes parasites of man.
- Nematoda varies in their sizes.
- Sexes are separate and generally exhibit considerable sexual dimorphism.
Classification of Nematoda:
- Aphasmida – lacking phasmids, caudal chemoreceptor.
- Phasmida – with phasmids.
Intergumentary System of Nematoda:
Consist of a non-nucleated cuticula secreted from underlying epithelium, three layers; namely:
- Cuticular or hyaline layer
- Epithelial or sub-cuticular layer
- 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:
- Direct – homogonic, don’t require an intermediate host, from egg, they developed into the infective stage.
- Indirect – heterogenic, require 1 or 2 intermediate host for the development into an infective stage.
Manner of Infection of Nematoda:
- Ingestion of eggs thru contaminated food or drinks.
- Ingestion of the encysted larva.
- Through skin penetration by filariform larva.
- Thru bite of arthropods or insect vectors as in filarial worms.
- Manner of transmission is still unclear.
Modes of Attachment of Nematoda:
- Oral attachment by sucking.
- By anchorage with their attenuated eggs.
- By penetration of tissues.
- Retention in the mucosal folds, producing pressure against it.
Means of Nutrition of Nematoda:
- Sucking and ingestion of blood.
- Ingestion of tissues.
- Feeling on intestinal contents.
- Ingestion of nourishment from body fluids.