In this article we will discuss about Monocystis:- 1. Habit, Habitat and Structure of Monocystis 2. Locomotion of Monocystis 3. Nutrition 4. Respiration 5. Excretion 6. Reproduction.
Habit, Habitat and Structure of Monocystis:
Monocystis lives as an endoparasite in the seminal vesicle of earthworms. The various phases of its life cycle become complete within the seminal vesicle.
Structure:
The trophozoites are fusiform in shape (Fig. 10.31). The outer covering of the body is called the pellicle which is smooth and thick. Within the pellicle the cytoplasm is differentiated into an outer non-granular cortex or ectoplasm and an inner granular medulla or endoplasm.
The endoplasm is rich in granules of glycogen-like carbohydrate, lipid droplets and other inclusions. Just below the pellicle, there are fibre-like contractile structures called myonemes. The nucleus is placed centrally. Food vacuoles and contractile vacuoles are absent.
Locomotion of Monocystis:
The wriggling movement of the otherwise sluggish monocystis is brought about by the contraction and expansion of the myonemes which are arranged in lines below the pellicle. The movement is slow but strong. The type of locomotion encountered in Monocystis is called gregarine movement.
Nutrition in Monocystis:
As an endoparasite the trophozoites of Monocystis live at the expense of the protoplasm of the sperm morula which remains stored in the seminal vesicle.
The trophozoites secrete digestive enzymes which act on the surrounding sperm cells of the earthworm and render them assimilable. The nutrient substances thus produced are absorbed through the whole cell surface or pellicle. Thus digestion in Monocystis is extracellular and the mode of nutrition is saprozoic.
Respiration in Monocystis:
Monocystis respires by the process of diffusion. As the parasite lives within the body of the earthworm the chance of getting free oxygen is very remote.
It is presumed that Monocystis gets its oxygen supply either by the process of fermentation of carbohydrate occurring in the body of the host or from the seminal vesicle, which gets its quota of oxygen from the blood of earthworm. The carbon dioxide produced diffuses out from the body and is finally eliminated through the blood of the host.
Excretion in Monocystis:
The metabolic wastes diffuse out of the body of Monocystis into the host tissue and are eliminated by the excretory organs of the host.
Reproduction in Monocystis:
Monocystis reproduces sexually and the process is always followed by asexual reproduction. In fact, the two processes are interdependent.
Sexual Reproduction:
During sexual reproduction two mature trophozoites, called gametocytes or gamonts, come close together and secrete around themselves a double- walled cyst. The cyst is called gametocyst or gamontocysts (Fig. 10.32A). The nucleus of each gametocyte divides a number of times and produces a large number of daughter nuclei (Fig. 10.32B).
The final nuclear division in case of Monocystis rostrata is meiotic or reductional in nature. The nuclei thus formed become arranged along the periphery of each gametocyte. Each nucleus collects a little mass of cytoplasm round it and becomes a gamete (Fig. 10.32C).
The gametes produced in each gametocyte are equal in number and similar in shape. Finally the line of demarcation between the gametocytes breaks and the gamete of one gametocyte fuses with the gamete of the other gametocyte. The fusion results in the formation of a zygote (Fig. 10.33D). The zygote formed inside a gametocyst is equal in number to the gametes present in each gametocyte.
Asexual reproduction:
The zygote which is called sporont or sporoblast secretes a hard covering round it. The covering is called zygocyst. The cysted zygote is now called the pseudonavicella for its boat-shaped appearance and resemblance to the genus Navicella (Fig. 10.33E).
Within the zygocysts the zygote undergoes three successive divisions, two of which are meiotic and one mitotic, and as a result eight fusiform sporozoites are formed (Fig. 10.33F).
On reaching the seminal vesicle of another earthworm the cyst wall breaks and the sporozoites are liberated (Fig. 10.34G). The sporozoites infect a sperm mother cell and leads an intracellular life (Fig. 10.34H). After some time it comes out of the cell in the seminal vesicle. It then resembles a trophozoite in appearance, but numerous tails of the earthworm sperms project from its surface (Fig. 10.34I).
Soon it sheds off those tails and becomes a trophozoite (Fig. 10.34J) and thus the life cycle becomes completed (Fig. 10.35). These trophozoites are haploid individuals and the gametes are haploid. This zygote is the only diploid stage in the life cycle.
