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Term Paper on Monocystis

Term Paper Contents:

  1. Term Paper on the Introduction to Monocystis
  2. Term Paper on the Structure of Monocystis
  3. Term Paper on the Electron Structure of Sporozoite
  4. Term Paper on the Nutrition and Locomotion of Monocystis
  5. Term Paper on the Respiration and Excretion of Monocystis
  6. Term Paper on the Reproduction and Life History of Monocystis

Term Paper # 1. Introduction to Monocystis:

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Monocystis is an inhabitant of a part of the reproductive apparatus of the common earthworm. Various stages in the life history of this organism are invariably found in the seminal vesicles of the earthworm. The common species usually met with include M. pheretimi Bhatia and Chatterjee, and M. Llodidi Ghosh.

Monocystis occur as an endoparasite in the coelom and seminal vesicles of earthworm. It lives as intracellular parasite in its young stage when it lives in the bundle of developing sperms and becomes extracellular in its mature stage when it lives in the contents of seminal vesicles of earthworms.

Its infection is so wide that practically all mature earthworms are found parasitized by this parasite. However, the various allied genera of Monocystis are Nematocystis, Rhabdocystis, Enterocystis, Apolocystis, Dendrocystis, Zygocystis, Dirhynchocystis, Pleurocystis, Cephalocystis, Rhynchocystis, Choanocystella, etc.

Mixed infections of the species of Monocystis and its allied species are of common occurrence in earthworm. In case of mixed infections of an earthworm, it becomes difficult to recognize the stage of the parasite of respective genera, but the trophozoites of different genera are characterized by their definite form. Here, Monocystis has been chosen as a typical example to represent these gregarine parasites.

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Monocystis can be easily obtained for study in the laboratory. A sexually mature living earthworm is narcotized by adding a few drops of chloretone in water. It is dissected in a tray and its seminal vesicles are taken out and kept in a watch glass in 0.7/NaCl solution.

A paste of seminal vesicles is made corrosive sublimate (mercuric chloride in water) and a thin layer spread on a cover slip which is placed on a glass slide and examined under a microscope for stages. A permanent slide can be prepared by the usual technique of stating, dehydration, etc.

At present, acephaline or monocystid gregarines are represented by 150 known species belonging to 20 different genera. Earthworms are frequently infected with several species, as shown by the variety of trophozoites and cysts found in the same smear. Due to mixed infections, it is difficult to relate stages of life history present to any particular genus or species.

The genera within the family Monocystidae are defined on the characteristic shape of the most conspicuous stage in the life cycle, that is, the feeding trophozoite, which may be spherical (Apolocystis), elongated (Nematocystis), spindle-like (Monocystis), or may remain paired (Pleurocystis, Zygocystis) throughout life.

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Term Paper # 2. Structure of Monocystis:

The young and growing trophozoite is a minute nucleated body found in the central protoplasm of one of the collections of the developing spermatozoa or sperm morula. It feeds and grows at the expense of the protoplasm around it until all the protoplasm has been consumed. Thereupon the trophozoite is found surrounded by the tails of dead spermatozoa of the earthworm, for a time, and appears like a ciliated organism. Ultimately these spermatozoa are detached and the trophozoite becomes free.

The mature trophozoite is fusiform limited externally by a thick smooth and porous pellicle (also called ectocyte). Its cytoplasm has an outer layer, ectoplasm (cortex), and an inner layer endoplasm (medulla). The ectoplasm may be differentiated into an outer homogeneous sarcocyte and an inner myocyte.

In the myocyte of the ectoplasm are found longitudinally running tracts of cytoplasm called myonemes, specially developed contractile structures. In some species circular myonemes are also present. Within the endoplasm is the nucleus, which is surrounded by a delicate nuclear membrane, and contains a clear liquid in which are suspended denser bodies called nucleoli. Chromatin is distributed throughout the nucleoplasm. The endoplasm contains other inclusions including Golgi material, chondrios (mitochondria), paraglycogen or zoomylum, the refractile carbohydrate granules, etc.

Term Paper # 3. Electron Structure of Sporozoite:

The electron structure of sporozoite reveals that it possesses all typical structures seen in protozoans, i.e. the Golgi body, mitochondria, nuclear components, etc., are as usual. In addition, pellicle shows longitudinally arranged contractile microtubules.

In the anterior end a pair of elongated reservoir like roptries are seen which secrete some secretion that helps the trophozoite in penetrating through the host tissues. The anterior end also shows the presence of conoids and micronemes, whose functional nature is not definitely known.

Within the pellicle, the cytoplasm is well differentiated into an outer layer of firm, clear cortex or ectoplasm and an inner mass of finely granular medulla or endoplasm. The ectoplasm is further made of three layers, an outer epicyte, a middle clear sarcocyte and an inner myocyte, containing a network of longitudinal as well as transverse contractile myoneme fibrils, responsible for the characteristic contractions and relaxations of the body. The more fluid and opaque endoplasm is laden with small granules of paraglycogen, fat globules and other reserve food materials. Sometimes volutin, a protein rich in phosphorus and nucleic acid, is also present.

Parapodia, cilia flagella, contractile vacuoles, food vacuoles mouth, gullet, etc., are totally absent due to its parasitic mode of life. Electron microscopy also reveals the presence of Golgi bodies and mitochondria, the latter being more numerous near the periphery.

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Term Paper # 4. Nutrition and Locomotion of Monocystis:

Nutrition:

The parasite at the feeding stage inhabits the seminal vesicles of the earthworm and it is known as the trophozoite (Gk. trophos, to feed; zooit, the animal). It lives at the expense of the sperm mother-cells of the earthworm, and consequently these cells of the host could not develop into sperm. The parasite absorbs, through the entire surface of its body, the nutrient fluid intended for ripening of the spermatozoa of the earthworm.

Locomotion:

The trophozoites show slow wriggling movement brought about by the rhythmical contractions of the myonemes present beneath the pellicle. Such movement’s characteristic of the groups Gregarinida to which Monocystis belongs is called as gregarine movement similar to the euglenoid movement of Euglena.

Term Paper # 5. Respiration and Excretion of Monocystis:

Respiration:

The actual mechanism of respiration in Monocystis is not known. It is believed that the parasite obtains oxygen by diffusion through its pellicle from the cell contents of host’s sperm moruia, when the trophozoite is within it, or from the fluid of the seminal vesicle. The mitochondria synthesize respiratory enzymes for oxidation reactions involved in aerobic conversion of pyruvic acid to CO2 and water.

Excretion:

The waste products formed inside the body of the parasite escape in solution by diffusion through the surface of its body.

Term Paper # 6. Reproduction and Life History of Monocystis:

Two individuals come together and round themselves off forming a pair. The pair becomes surrounded by a hard coating which they secrete; so that, the pair lies within a cyst called the gametocyst. The nucleus of each member of the pair divides repeatedly giving rise to a large number of daughter nuclei.

The daughter nuclei migrate to the periphery of the cytoplasm, where each nucleus (daughter nucleus) becomes surrounded by a little mass of protoplasm. The nuclei with their enveloping protoplasm are called gametes or isogametes and the individual bearing them is known as the gametocyte.

The line of separation between the uniting pair now vanishes, and gametes of one unite with those of the other forming the zygotes. So, if n gametes have been produced in each member by division of its nucleus there would be by the union of the gametes in parts, n zygotes within the cyst.

Each zygote secretes a membrane or capsule around it and it is now known as the sporont or sporoblast. In this state it is also called the pseudonavicella owing to the boat-shaped appearance of its capsule which is rendered hard by deposition of chitin. The nucleus of each sporont divides repeatedly giving rise to eight elongated forms called the sporozoites.

These remain enclosed in a batch of 8 within each chitinoid capsule. Thus, if n zygotes (spores) have been produced there would be n capsules of 8n sporozoites within the common cyste. No further development of these parasitic forms is possible until a new host is found.

If the earthworm harbouring these cysts dies and its body disintegrates in the soil, the capsulated sporozoites are liberated in the soil. Again, if the earthworm infected with the cysts, the eaten up by a bird, the capsules are cast out into the soil with the bird’s faeces, the sporozoite capsules resisting the action of gastric juice of birds.

The soil containing the capsules (or the cysts) when swallowed by another earthworm, the hard coatings of the capsules are dissolved within the alimentary canal of this earthworm and the sporozoites are liberated there. Each sporozoite is falciform or sickle-shaped and it bores its way from the alimentary canal to the sperm mother-cell of the earthworm and thus the parasite completes the life cycle.

However, the life cycle of monocystis exhibits an alternation of a sexual generation of gametocytes with a sexual generation of sporozoites.

Mode of Transference:

The mode of transmission of sporocysts from one earthworm to another is not well known but the following methods are presumed:

1. When an infected earthworm dies and decays, the spores get scattered in the soil. This infected soil when eaten by another earthworm; the sporozoites enter the gut of fresh host.

2. When an infected earthworm is eaten by a bird, the spores are not digested and are passed out along with faeces on the soil. This soil if eaten by another earthworm, the cyst wall is dissolved and the sporozoites finally enter the seminal vesicles.

It is possible that the spores are transferred from one earthworm to another during copulation when there is exchange of sperms from the seminal vesicles of one host to another.

Host Parasite Relationship:

Though nearly all earthworms are found to be infected with Monocystis even then they cause no appreciable damage to the earthworms. The parasite destroys the sperms of the earthworms, no doubt, but this does not affect the fertility of worms because they produce sperms in abundance.

The earthworms appear to be able to combat the parasites by forming resistant protective envelope around the trophozoites and also by killing the spores by phagocytosis. On the other hand, the parasite shows various structural, physiological and reproductive adaptations so that it leads its life successfully and maintains the continuity of its race.

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