Monocystis
Q.12. Describe the life history of monocystis. (2006)
Related Questions -
Q. Write short notes on Monocystis and its transmission. (2012)
Q. Write note on sporocyst on Monocystis. (2011)
Q. Give a detailed account of life cycle of Monocystis. (2013)
Q. Write notes on monocystis. (2015)
Q. Write short note on Sporocyst stage of Monocystis. (2018)
Ans. Life History of Monocystis: -
Monocystis is monogenetic i.e. its life cycle is completed in a single host which is mostly the earthworm. The life cycle proceeds as follows -
(1) Gamontogamy: -
This is a method of sexual reproduction which involves the pairing of gamonts, formation of gametes and fertilization. It takes place as follows -
(a) Syzygy: -
After a period of feeding, growing and wandering about, each trophozoite becomes an oval reproductive body, the gamont or gametocyte. The gametocytes become more round and unite in pairs. The two then secrete a common resistant and protective cyst wall the gametocyst around themselves. The cyst wall has two layers, an outer thick and rigid ectocyst and an inner thin endocyst. Within the cyst wall the gametocytes never fuse or conjugate. This type of pairing of the gametocysts is referred to as syzygy.
(b) Gametogony: -
Within the gametocyst each gametocyte undergoes nuclear multiplication by mitosis. The nuclei thus formed move to the periphery and each gets surrounded by a small amount of cytoplasm. These uninucleate cytoplsamic bodies become free as gametes leaving a certain amount of residual cytoplasm in the center of the gametocyst. The gametes are anisogametes and contain four chromosomes (haploid number) each.
(2) Sporogony: -
Each zygote which is first spherical, transforms itself into a single-walled unicellular and boat shaped body called the sporoblast. It soon secretes a thick cyst wall the sporocyst and becomes a spore. It possess a mucoid plug at either end. The spore now acquires the characteristic form of a boat resembling a diatom of the genus Navicella. This stage is therefore frequently referred to as pseudonavicella. Within the sporocyst the spore undergoes three successive nuclear divisions producing eight daughter nuclei the first division being the reduction division. Each daughter nucleus gets surrounded with a cytoplasmic mass resulting in the formation of eight minute, elongated and sickle shaped haploid sporozoites. All these changes occur within the original cyst wall formed at the time of syzygy.
At this stage the original cyst walls each containing numerous spores filled with the sporozoites rupture and the spores are liberated into the cavity of the seminal vesicle. The rupture of the original cyst wall may be assisted by the swelling of the residual cytoplasm. The liberated spores wait for their transmission to a new earthworm host.
(3) Transference: -
The exact manner in which the spores of monocystis are transmitted from one worm to another is not known with certainity.It may take place in any of the following ways -
(a) During copulation (b) Death of host
When the host worm dies and decays the spores get scattered in the soil. When the infected soil is eaten by another worm, these also enter its alimentry canal.
(c) By Birds: -
When the infected worm is devoured by a predator such as bird the spores would pass out unaltered with its excrement and subsequently swallowed up by other worms.
(d) Automization: -
In certain species of Monocystis whose spores are found in the coelomic cavity of the posterior segments of the earthworm the posterior body is autotomized and the spores are liberated in the soil. With the ingestion of the contaminated soil by a fresh earthworm the spores too are ingested.
Within the anterior part of the alimentry canal of a new host the sporocyst breaks or possibly dissolves by the action of the digestive enzymes. The sporozoites contained within each spore becomes free into the lumen of the alimentry canal.
(4) Sporozoites: -
The sporozoites are spindle shaped and minute protoplasmic bodies. Each contains a single nucleus one or more mitochondria, golgi complex and the outer pellicle. Their secretion helps in peneteration through the tissues.
(5) Invasion of Seminal Vesicles: -
With the help of contractile action of the sub – pellicular microtubules, the sporozoites make active movements. They make their way into the epithelial cells of the gut mucosa, one sporozoite entering one cell.Here they grow in size and then escape into the seminal vesicles. In the seminal vesicles each sporozoite enters a central cell of the sperm morula.
(6) Development of Trophozoite: -
In the sperm morula the sporozoite feeds and grows into a young trophozoite. It exhibits hair like sperm tails around its body which are the remnants of degenerating sperms. With the degeneration of the sperm tails as well, the trophozoite becomes free in the cavity of the seminal vesicle as an adult trophozoite. Thus the trophozoites are at first intracellular and later extracellular.
Q.13. Write short note on structure of trophozoite of monocystis. (2017)
Ans. Structure of Trophozoite of Monocystis: -
Monocystis is an extracellular in the parasite in the seminal vesicles of earthworm.
Shape and size: -
The adult feeding and growing stage of Monocystis is known as trophozoite stage. The young trophozoite is small and ellipsoidal. It remains embedded in a group of developing spermatozoa. It appears ciliated as the tails of the dead sperms remain attached to it.
The mature trophozoite is elongated, spinble-shaped and dorsoventrally flattened worm-like creature. It visible to the naked eye as a white thread.
Pellicle: -
The body of Monocystis trophozoite is bounded by a thick firm but elastic pellicle. It is formed of nitrogenous matter. It may hair-like processes. It contains contractile microtubules.
Cytoplasm: -
The cytoplasm has a sharp differentiation between outer clear ectoplasm and inner granular endoplasm. Ectoplasm is further divided into three layers (i) outer epicyte, (ii) middle sarcocyte and (iii) inner myocyte. Myocyte consists of longitudinal and transverse contractile fibrils or myonemes, which are supposed to enable the trophozoite to perform its charcteristic metabolic movements.
The endoplasm contains in abundance the granules of paraglycogen (a special form of glycogen),fat globules and sometimes volutin, a protein rich in phosphorus and nuclei acid.
Nucleus: -
Nucleus is single and vesicular with spherical or ellipsoidal form. It contains usually one nucleolus or karyosome, (sometimes more), which stains deeply with iron haemetoxylin. Nuclear membrane is delicate and bears pores. Nucleoplasm contains four chromosomes (haploid number).