So far only the flatworms have been studied; however, there are two other Phyla of worms, namely:
- Phylum Aschelminthes; and
- Phylum Annelida.
The above-mentioned are the roundworms and the true segmented worms respectively. In this lecture these will be studied. In Lecture 1, the animal kingdom was outlined in a diagramme. In this diagramme, the student will be able to see that the Aschelminthes are classified under Acoelmata, as they do not possess a true body cavity. The Annelida, however, do possess a true body cavity with a lining and these are thus classified as Eucoelmata.
This phylum consists of one class, Nematoda, and hence they are often referred to as the nematodes. Nematodes have elongated non-segmented bodies, which are more or less circular in cross-section. Many of them are parasites, but the vast majorities are free living in water. Agriculturally, nematodes are a very important class, as there are many of them, which parasitise Man, his animals and his crops.
Human Parasites: Hookworms Wireworms
Stock Parasites: Wireworms (Haemonchus contortus), Bankrupt Worms (Trychostrongylus spy) Ascaris Worms (Ascaris.spp)
Plant Parasites: Eelworms – mainly root knot eelworm (Meloidogyne javanica)
This is just to name a few, this study will concentrate on Ascaris worms and Eelworms. The worms are unisexual, with male and female forms. The worms have an alimentary tract, i.e. a gut, and muscle. (Refer to Figure 1). This shows a cross-section of a typical nematode. Nematodes are covered with a protective cuticle. They are more advanced than the flukes and they also possess a primitive backbone, called a Notocord. This is a skeletal structure, and is not made of bone.
Figure 1: Cross Section of a Nematode
BOTANY AND ZOOLOGY – LEARNER GUIDE
Figure 2: Life Cycle of Ascaris lumbricoides
Haemorrhage: an escape of blood from a ruptured blood vessel. ASCARIS WORMS
Ascaris worms parasitise mammals (these are animals which suckle their young). The example that will be studied in this lecture is the ascaris worm of the pig – the genus Ascaris. It is believed that there are two species that infect pigs, namely the Ascaris suis and Ascaris lumbricoides. The two species are, for all intents and purposes, the same. The adult worms are long creamy colored worms. The males measure up to 25 cm long
and the female up to 45 cm long. They inhabit the small intestine of the pigs and can cause severe damage by initiating haemorrhage, and even causing physical obstruction.
The adult worms live in the small intestine of the pig, and the female lays about 200,000 eggs per day. The eggs pass out into the faeces. After reaching the exterior, the eggs take about 10 days to develop embryos. When swallowed, the eggs hatch in the intestine. If the eggs are not ingested, they can remain viable for a number of years. Hot dry conditions and direct sunlight will kill them in a few weeks. After the eggs have hatched in the intestine, the larvae (0.3 mm long) burrow into the capillaries of the intestinal wall. They are carried in the blood for approximately 4 – 6 days to the lungs, where they remain for 1 – 3 weeks. Here they grow and live for about a week or longer and
then enter the alveoli and bronchioles, migrate up the windpipe to the epiglottis and then fall down the oesophagus to the gut, where they settle and mature for 8 – 9 weeks and then migrate to the small intestine, where they mate and the cycle continues.
|Gelatinous: having a jelly- like consistency.
Ascaris worms cause their most dramatic effects in young pigs as when the worm adults die, they release poisons.
ROOT- KNOT EELWORM
There are a number of species of nematodes which infect plant roots and cause very severe damage in some crop. The main species of plant nematode in Central/Southern Africa is the one causing Root Knots, and is therefore called Root Knot Eelworm. The organism is Meloidogyne javanica. The Root
Knot Eelworm is a major pest of tobacco, and without proper controls, tobacco crops can be completely ruined. These nematodes are microscopic in size and live in the soil for a number of years. They can live on almost every plant with notable exceptions, such as Chloris gayana (Rhodes Grass). Fields are planted with this grass for
3 – 4 years to starve the nematodes and to enable the farmer to grow tobacco.
The larvae can survive in the soil for up to 2 years. The young larvae bore into the roots of susceptible plants growing near them, causing galls to form on them. When mature, the female lays eggs in a gelatinous mass which bursts out of the side of the root or may remain within. The cycle takes 6 weeks or less in warm weather. The galls are deformities and are quite distinct from natural root nodules.
The Annelida are the true segmented worms, the main example being the earthworm. The earthworm has a segmented body covered in hairs called cheotae. The earthworm (Lumbricus terrestis) is important because it ingests soil and defecates a very enriched soil. These worms aerate the soil and mix it. During its life time the earthworm moves tonnes of soil around.