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Term Paper on Vorticella

Term Paper Contents:

  1. Term Paper on the Introduction to Vorticella
  2. Term Paper on the Habits and Habitat of Vorticella
  3. Term Paper on the Structure of Vorticella
  4. Term Paper on the Locomotion and Nutrition of Vorticella
  5. Term Paper on the Respiration, Excretion and Osmoregulation in Vorticella
  6. Term Paper on the Culture and Behaviour of Vorticella
  7. Term Paper on the Reproduction of Vorticella
  8. Term Paper on the Conjugation of Vorticella
  9. Term Paper on the Post-Zygotic Development of Vorticella

Term Paper # 1. Introduction to Vorticella:

ADVERTISEMENTS:

Vorticella (L., vortex = whirl pool) is a ciliate which is stalked and has over 200 species, most of them are found in freshwater ponds which are rich in minerals but with no putrefaction. Some species are marine, some are epizoic, and a few live within their hosts. The commonest species is Vorticella campanula, but V. picta, V. monliata. V. nebulifera and V. microstoma are also fairly common. Vorticella campanula is described here in detail. They are characterized by the extensive oral ciliature and the lack of somatic ciliature. The adults are mostly sessile. Verticella is a common fresh water solitary genus, attached to the substratum by a highly contractile stalk.

Term Paper # 2. Habits and Habitat of Vorticella:

Vorticella is an extremely common peritrichous ciliate often found in freshwater ponds, lakes, rivers and streams, etc. Unlike Paramecium, which is free swimming, Vorticella is a sedentary or fixed form. There are about 200 species, all solitary but never colonial. Often several individuals occur socially in large groups anchored by their large contractile stalks to aquatic plants, animals, stones, etc.

Under certain conditions, the body becomes detached from its stalk and swims freely. They occur most abundantly in still water containing rotting organic matter, feeding largely on bacteria of decay. But some species, such as vorticella campanula and V. nebulifera, can live only in uncontaminated waters, where bacterial growth does not become too great.

ADVERTISEMENTS:

Some species are marine, some are epizoic and a few live within their hosts. V. microstoma is very common in freshwater and frequently appears in laboratory infusions. V. convallaria is interesting being the first microscopic animal discovered and seen by Leeuwenhoek in 1675.

Term Paper # 3. Structure of Vorticella:

Shape, Size and Colour:

Vorticella is a stalked ciliate. Its body is like a bell at the bottom of which a stalk is attached, many individual variations are found in the shape of the body and the stalk. The size of the bell of the largest species, Vorticella campanula is about 157 x 99 microns and the length of the stalk is from 53 to 415 microns. The colour of Vorticella nebulifera is greenish while that of Vorticella companula is bluish.

ADVERTISEMENTS:

External Structure:

The stalked body of vorticella is divisible into two parts:

1. Bell:

Its shape is like that of a solid inverted bell.

2. Stalk:

Stalk of Vorticella is a long thread like structure whose one end is attached to the bell and the other to the substratum. Stalk is long, uniformly thin, un-branched and highly contractile. It remains devoid of cilia.

1. Bell:

Its structure can be defined under the following heads:

(a) Peristome:

ADVERTISEMENTS:

The broader free end of the bell bears a slightly convex central area, termed the peristomial disc. Its outer margin is thickened so as to form a prominent rim or collar, the peristomial border or lip. It is separated from the raised central disc by a shallow, circular and marginal depression, known as the peristomial or oral groove. Cilia are inserted in this groove. When the disc is retracted, the collar closes over it.

(b) Vestibule:

A part of the edge of the central disc is present in the form of a depression called vestibule or infundibulum. The roundness of the lip becomes distorted due to the presence of the vestibule. A cytostome is found at the base of the vestibule. It opens into a narrow cytopharynx which is found in the form of a groove in endoplasm. It remains open at the time of feeding but at other times it is kept contracted.

(c) Adoral Cilia:

Most of the bell-shaped body of Vorticella is without cilia. The cilia are restricted only to the peristomial part. Three concentric rows of adoral cilia are found in the peristomial groove. They are present in two circles. Two rows of cilia are found in the inner circle. These cilia remain straight and always moving. Only one row of cilia is found in the outer circle.

The cilia of this row hang horizontally towards the outer side on the lip. They direct the food particles towards the vestibule. The aboral cilia are fused with each other at their base, but are free at their distal ends. Both the spiracles of cilia are curved in such a way that they form about one and a half anti clock-wise spiral on the peristomial disc. Both spirals of cilia extend up to the vestibule.

The two inner rows of cilia extend together along the inner wall of the vestibule, whereas the outer row of cilia is elongated and its cilia unite together to form an undulating membrane along the outer wall of the vestibule. The cytopharynx is devoid of cilia. The food particles are sent to the cytopharynx by the vestibule as a result of the movement of cilia. In the cytopharynx, a small food vacuole is formed around the food particles.

Cytoplasm:

The body of cytoplasm is differentiated into an outer layer of clear ectoplasm and an inner granular fluid of endoplasm which is not present in the stalk.

(a) Ectoplasm:

The ectoplasm has no trichocysts. It consists of an elastic outer pellicle and a thicker inner layer of contractile fibres or myonemes.

(i) Pellicle:

The pellicle covering the bell also lines the vestibule and is especially thick at the base of the bell. It is devoid of cilia but their basal granules are present in circles showing that their cilia are lost. The basal granules can be demonstrated by the klein-silver-line method. Besides, on closer examination, the pellicle shows indistinct circular striations where the cilia might have been.

(ii) Myonemes:

The myonemes form a system of variously running fibres which function differently on contraction. The longitudinal myonemes shorten the body, the oblique myonemes pull the disc inwards and the circular myonemes contract and close the peristomial border over the cilia and the disc. The myonemes, running parallel down the sides of the bell, are more visible at the base where they converge before entering the stalk.

(b) Endoplasm:

The granular endoplasm contains various inclusions, such as nuclei, contractile vacuole, food vacuoles, etc.

(i) Nuclei:

The endoplasm contains a large, elongated curved, sausage-like or horseshoe-shaped macronucleus. It is highly polyploid with a large amount of chromatin material scattered in its nucleoplasm. It is visible in the living specimen. Its lower end is slightly bent, while the upper end forms a horizontal limb beneath the peristomial disc. A tiny micro-nucleus lies in close association with the macronucleus. It is rarely seen in the living animalcule.

(ii) Contractile Vacuole:

There is always present a clear contractile space near the vestibule. This is called contractile vacuole. In the fully dilated condition, its diameter is about 7 microns. Like Euglena in Vorticella also it controls the amount of water in the body. Upon its contraction, the substances collected in its pass into a small reservoir which opens by a small canal into the vestibule. In this manner the substances of the reservoir reach the vestibule from where it is sent out of the body. Two contractile vacuoles are found in some species of Vorticella such as V. picta and V. monilata.

(iii) Food Vacuoles:

Many food vacuoles are found scattered in the endoplasm.

Cytopyge or Anal Spot:

It is a temporary aperture opening into the vestibule. Undigested food is sent out of the body through this aperture.

2. Stalk:

The bell-shaped body is attached to submerged weeds or other substance by means of a uniformly narrow, long, un-branched and contractile stalk. Cilia are not found in this part. The myonemes of stalk are united together to form a spirally twisted axial filament in its centre. A layer of cytoplasm is present all-round the stalk and outside it is situated a layer of pellicle over which a thin cuticle is present. Some bacteria, living as commensal, may also be found on the stalk.

Term Paper # 4. Locomotion and Nutrition of Vorticella:

Locomotion:

Vorticella does not move freely because it is usually found fixed aborally by its long highly contractile stalk. However, with the help of stalk and myonemes, the bell sways to and fro in the surrounding water like a flower in a breeze. The individuals of a group move of their own way. The detached individuals swim freely by means of cilia and are referred to as telotrochs.

Nutrition:

It is holozoic like paramecium. The cilia of the peristome and the disc produce a current of water by which small organic particles fall on the disc, from where they are carried into the vestibule. Now undulating membrane carries them to the cytopharynx. The movement of the food is aided by undulations of the two inner rows of cilia.

At the base of the cytopharynx the food particles along with some water form food vacuoles one after the other. Movement of food vacuoles in the endoplasm is in an irregular cyclosis. According to Noland and Finlay (1931) the inward feeding current is directed downwards the vestibule between the inner and outer ciliary membranes. The outward or rejection current flows between the inner membranes and the wall of vestibule.

At the base of the cytophatynx the food particles are pinched off along with some water into the endoplasm forming food vacuoles one after the other. In the endoplasm the food vacuoles move in an irregular cyclosis and not like that of Paramecium. Digestion is similar to that of Paramecium and the contents of food vacuoles are at first acidic and then become alkaline, till absorption and assimilation of food.

Excess of digested food forms refractile glycogen granules in the endoplasm. The undigested food particles are also passed into the vestibule, through a permanent or temporary opening, the cytopyge or cytoproct, formed at a weaker spot of the ectoplasm.

Term Paper # 5. Respiration, Excretion and Osmoregulation in Vorticella:

Respiration and excretion in Vorticella is exactly performed in the same way by the process of diffusion through general body surface as in Amoeba and Paramecium.

Osmoregulation in Vorticella is performed by the contractile vacuole, as in other freshwater Protozoa. In Vorticella, contractile vacuole is single, large and pulsating usually situated between the disc and vestibule in the endoplasm. The contractile vacuole opens in the vestibule by a permanent opening; it pulsates rhythmically showing diastolic and systolic phases.

In fact, during diastolic phase, the excess of water drawn in the endoplasm by the process of osmosis is secreted into the contractile vacuole and during the systolic phase, the contractile vacuole expels out the excess of water into the vestibule. Thus, contractile vacuole helps in maintaining the water content in the body.

Term Paper # 6. Culture and Behaviour of Vorticella:

Culture:

It is prepared by making an infusion of hay and dead leaves in rain or distilled water. Let it for few days. After some days, a brownish scum will be formed on the surface.

Below this surface Vorticella will be present. This shows the presence of cysts in Vorticella.

Behaviour:

Vorticella exhibit high degree of contractility and irritability; it is extremely sensitive to any mechanical stimulus and also responds to external stimuli. When irritated, it’s all activities cease at once; the stalk is retracted and becomes coiled into closed spiral to reduce its size, then the disc is withdrawn and covered over by peristomial lip. Due to all these activities, its body becomes somewhat globular and remains motionless till normacy is restored.

Term Paper # 7. Reproduction of Vorticella:

Generally the reproduction takes place asexually by longitudinal binary fission. Sometimes, Conjugation occurs. Under favourable conditions, encystment also takes place.

A. Longitudinal Binary Fission:

This type of division passes lengthwise alone the oral-aboral axis of the body. At the time of this type of fission, Vorticella closes the peristomial part above the disc. The body elongates transversely. The contractile vacuole keeps on functioning during this division. The long and curved macronucleus contracts to become straight and is placed transversely in the middle of the body.

Now it divides amitotically and forms two daughter nuclei. At the same time, the micronucleus divides mitotically into two. With the division of the nuclear apparatus, a longitudinal groove appears in the middle of the free end due to which the peristome is divided into two parts.

This groove gradually progresses downward to divide the bell into two parts which are not equal in size. There is no stalk in the smaller part formed in the above manner whereas the parental remains attached to the larger part. A new spiral of aboral cilia and a contractile vacuole is formed in the smaller part.

Along with this, a spiral of cilia is also formed in the hinder region of the smaller part. This part now becomes cylindrical and breaks off from the parental stalk. It is called telotroch. It swims actively in water with the help of cilia present in its posterior part, keeping the aboral part forwards.

After swimming for some time it attaches itself to some submerged object with the help of a disc-shaped structure formed on its aboral part. This adhesive disc now forms a stalk with the help of which the telotroch is suspended in water. Soon the disc is lost. The bell-shaped body enlarges to form a new peristomial disc and soon a new adult Vorticella is formed. The process of binary fission is completed in about 20 to 30 minutes.

Out of the two parts formed by this process, the large part retains the parental disc and stalks, is called parent Vorticella. The smaller part is known as telotroch or offspring.

Sometimes in unfavourable conditions, a spiral of cilia appears in the posterior part of the body of Vorticella, and separates from the stalk after assuming the form of a telotroch. It swims to a suitable place and itself forms a new stalk after attaching to some object.

Sometimes, a double layered cyst is secreted around this stage attached to the parental stalk. The cyst now separates from the parental stalk. After the rupture of the cyst, a new posterior spiral of cilia is formed in it which swims like a telotroch and forms a new stalk for attachment in favourable surroundings.

Term Paper # 8. Conjugation of Vorticella:

Conjugation is a mode of sexual reproduction, which is very characteristic in Vorticella. The process of conjugation and syngamy was studied by Maupas (1888) in Vorticella nebulifera, and by Finlay (1943) in Vorticella microstoma.

However, the process of sexual reproduction in vorticella described hereunder is a generalized description; it can be studied in the following two phases:

(i) Formation of micro-and macro-conjugants, and

(ii) Conjugation of micro-and macro-conjugants and their fusion.

(i) Formation of Micro-Conjugant and Macro-Conjugants:

A Vorticella divides twice to form four daughter individuals called microzooids. Each of them forms a whorl of cilia in its posterior part and starts swimming after separating from the parental stalk. These micro-conjugants are smaller than telotroch and cannot transform into adults. They die if they fail to reach the macro-conjugant within 24 hours.

The trophic or vegetative individual becomes a macro-conjugant after certain nuclear modifications in it. It is like the adult animal in structure but has physiological difference from the latter. It attracts the micro-conjugants toward it.

(ii) Fusion of Conjugants:

While swimming, when a micro-conjugant approaches a macro-conjugant then it gets attached to the lower end of macro-conjugant near its stalk. Thus, both the conjugants come together.

Soon, cilia and pellicle of the micro-conjugant is thrown off and nuclear changes start taking place simultaneously in both the conjugants; the nuclear changes occur in the following way:

(a) The macronuclei of both disintegrate and are absorbed in their cytoplasm.

(b) The micronucleus of the micro-conjugant divides thrice so as to form 8 micronuclei but the micronucleus of the macro-conjugant divides only twice to form 4 micronuclei.

(c) 7 nuclei in micro-conjugant and 3 in macro-conjugant disintegrate.

(d) The one nucleus left in either conjugant moves towards the wall separating them.

(e) In the meantime, the wall separating them breaks and the two conjugants become one.

(f) The nuclei of both the conjugants now divide meiotically to form two nuclei in each. One of these nuclei disintegrates. The remaining nuclei of the micro-conjugant are now called the migratory or male pro-nucleus while that of macro-conjugants is known as stationary or female pro-nucleus.

(g) The male and female pronuclie now fuse to form a synkaryon or zygote nucleus.

(h) All the substance of the body of the micro-conjugant reaches in the macro-conjugant, therefore, it contracts and in the end disintegrates.

Term Paper # 9. Post-Zygotic Development of Vorticella:

Fusion is complete and there is no separation after conjugation. The little male or micro-conjugant degenerates and its pellicle falls off after its contents have been sucked up into the macro-conjugant. Within the zygote, the synkaryon divides thrice mitotically resulting into eight micronuclei of which seven enlarge to form macronuclei.

The zygote cell and its remaining micronucleus now divide, forming two daughter cells, each receiving one micronucleus. But four macronuclei go to one daughter cell and the remaining three to the other. Each daughter cell and its micronucleus divide twice. The daughter cell with four macronuclei forms four daughter individuals, each with one micronucleus and one macronucleus.

The daughter cell having three macronuclei gives rise to only three individuals, each having one macronucleus and one micronucleus. The seven daughter cells thus produced begin to grow, acquire stalks and finally become adults.

C. Encystment:

Under unfavourable conditions, when there is excessive dryness or cold, Vorticella either forms a girdle of cilia in its posterior part or secretes a cyst around itself and separates from the stalk. In the encysted condition, the animal passes over the unfavourable time and with the onset of the favourable conditions it breaks free from the cyst. It swims for some time and then attaches itself to some object in water. It forms a stalk and becomes adult.

Vorticella shows advancement in conjugation over Paramecium. The two conjugants Paramecium are similar, unite only temporarily for an exchange of nuclear material and there is no fusion of cytoplasm. But the ex-conjugants reproduce further by fission. While in Vorticella, the two conjugants are dissimilar or anisogametes and their cytoplasm as well as nuclei fuse permanently to form a zygote which reproduces further by fission. Unlike Paramecium, Vorticella also shows a differentiation of sex in its dimorphic gametes. The sexual process in Vorticella may be said to be intermediate between conjugation and syngamy.

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