PARASITES AND
PARASITIC DISEASES
OF DOMESTIC ANIMALS


The Nematodes

Internal Morphology

The basic nematode body consists of an outer tube (the body wall) enclosing an inner tube (the digestive tract). The fluid-filled body cavity lies between these two tubes and contains the reproductive tract. This body cavity is a pseudocoelom because, unlike a true coelom, it does not possess a cellular lining or peritoneum. There is no vascular system in the nematodes, instead the circulation of nutrients in the pseudocoelom is assisted by body movements and locomotion.

The body wall has three layers: cuticle, hypodermis and an inner layer of muscle cells. The hypodermis, lying beneath the  cuticle, is relatively thin and is a syncytium of cells in the majority of nematodes of veterinary importance. The primary function of the hypodermis is to secrete the cuticle.

The hypodermis has four longitudinally thickened areas or cords that protrude into the body cavity in the mid-dorsal, mid-ventral and lateral regions.The dorsal and ventral cords contain longitudinal nerve trunks while the lateral cords contain excretory canals.

Internal to the hypodermis are one or more layers of longitudinally arranged striated (somatic) muscles. These are closely associated with the hypodermis and also connect to the cuticle by fibers passing from the contractile part of each muscle cell. Each muscle cell consists of a contractile part with muscle fibers and a non-contractile part or cell body containing the nucleus, mitochondria and other organelles in addition to glycogen and lipid stores. Muscle cells of nematodes are unusual because they are not innervated by nerve fibers as is the case with muscles of other animals. Instead, processes from muscle cell bodies link muscle cells to the nerve trunks.

Movement of Nematodes

Nematodes are covered by an outer cuticle that is structured so as to maintain the body at a constant diameter while allowing longitudinal flexibility. Since nematodes have longitudinally arranged but no circular muscles, contraction of muscles bend the body dorsally or ventrally.Since the cuticle prevents radial swelling, contraction of one muscle group will stretch another. This situation ensures that the dorsal and ventral muscles will act antagonistically to each other, allowing nematodes to move in a sinusoidal manner by undulating waves of muscle contractions. These movements allow nematodes to move among soil particles and swim in body fluids of a host.

Click here to view a cross sectional drawing of a female nematode at the level of the intestine.

Click here to return to the drawing of a nematode at the level of the esophagus

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Parasites and Parasitic Diseases of Domestic Animals
Dr. Colin Johnstone (principal author)
Copyright 1998 University of Pennsylvania
This page was last modified on February 11, 2000