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In this article we will discuss about Vorticella:- 1. Habit and Habitat of Vorticella 2. Structure of Vorticella 3. Reproduction.
Habit and Habitat of Vorticella:
Vorticella is popularly known as bell animalcule. It grows on the stems of fresh water or marine plants and appears as white fringes to the unaided eyes. Vorticella is solitary but its related form Carchesium are colonial.
Structure of Vorticella:
Structures of vorticella suggest an inverted solid bell having a long handle (Fig. 10.44A). The base of the handle or stalk remains fixed to the object of anchorage and is capable of contraction. The handle is formed by a prolongation of the body, encased in cuticle and it contracts by means of myoneme. The bell is provided with a thick margin. The depressed disc-like structure within the margin is called the peristome.
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The depression bears an opening which leads into a distinct passage, called the vestibule (Fig. 10.44B). A permanent anus or cytopyge is situated close to the vestibule.
Cilia are restricted to the mouth region and are arranged in inner and outer concentric rows and form an undulating membrane in the vestibule. The cilia have the usual structural pattern. The macronucleus is large and horseshoe-shaped while the micronucleus is small and round. A single contractile vacuole is present, though food- vacuoles are many.
Reproduction in Vorticella:
Vorticella reproduces both asexually and sexually (Fig. 10.45). Asexual reproduction takes place by means of usually unequal longitudinal binary fission. During division the body shortens and nuclei divide first. The macronucleus divides amitotically and micronucleus divides mitotically.
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The bell divides into two halves by a vertical constriction which begins in the middle of the free end. One of the halves develops a basal circlet of cilia and separates forming a new free- living individual. After some time it fixes itself by means of a short adhesive disc, called scopula.
From the scopula a new stalk arises and the individual metamorphoses into adult. The free-swimming stage is called telotroch. Sometimes vorticella grows a posterior circlet of cilia and detaches from the stalk to lead a free-swimming life.
Sexual reproduction is performed by conjugation. As gametes are of unequal sizes, the reproduction is called anisogamy. Each individual divides thrice forming eight microzooids. The microzooids swim about by means of posterior girdle of cilia. It differs from telotroch being much smaller in size.
The microzooids survive only for 24 hours and must conjugate with macrogamete within the period. The stationary macrogamete resembles the normal form. It is able to attract the microgamete for two hours. The micro- gamete during conjugation fixes itself on the lower part of the macrogamete.
The macro- nuclei of both the gametes disappear and their micronuclei re-organise to form male and female pronuclei. When the partition wall between the two dissolves, the two pronuclei unite to form synkaryon or zygote nucleus. The fertilised individual is called zygote. From the zygote develops a new vorticella.
