Ciliate the unicellular protists are the close relative of the eukaryotic crown taxa. This implies that around the phylogenetic trees they sustain as a single lineage on the cluster of fungi, animals, and plants. Also commonly known as ciliophorans, they belong to the family of phylum Ciliophora. The main characteristic of ciliate is that it is formed with a number of cilia.
Let’s learn about Ciliates, it's characteristics, habitat, reproduction process which covers up the cilia anatomy.
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Ciliates are ciliated protozoans that are made up of hair-like organelles called cilia. Ciliates are distinguished from other protozoans such as sporozoans, amoeboids, and flagellates due to the presence of cilia that are used for locomotion and membranelles used for feeding. Cilia assists in locomotion, crawling, swimming as well as in sensation and feeding. Ciliate has two types of nuclei that distinguish it from other members of the family namely small diploid micronucleus and larger polypoid macronucleus.
They are believed to be the most complex unicellular organisms. Ciliates feed on other microorganisms that include algae, bacteria, etc.
Ciliate are normally found in aquatic and moist habitats such as soils, rivers, oceans, ponds, and lakes. Examples of ciliates include Tetrahymena, Vorticella, Paramecium, Coleps, Colpoda, Balantidium, Didinium, Stentor, etc.
Ciliate anatomy has numerous unique characteristics that distinguish it from other protists. Some of them are mentioned below:
Ciliates are referred to as ciliated protozoans due to the presence of cilia. Cilia is nothing but the hair-like projections or organelles that originates from the cell cortex. Cilia are associated with the movement of the organism. Apart from moving from one place to another, cilia also let the ciliates sense the change in the environment. This helps them to respond and react effectively. The cilia are short and numerous and cover almost the entire surface of the being. Some organisms such as Euplotes and Aspidisca use cilia to move while some organisms such as paramecium are known as free-swimming ciliates as they swim in water without the use of cilia.
Ciliates are formed out of two nuclei namely macronucleus and micronucleus. The micronucleus is composed of two copies of chromosomes and hence is termed a diploid nucleus. In a single cell, there can be one micronucleus or many of them. The macronucleus consists of short pieces of DNA. At the time of cell division, the micronuclei undergo mitosis and the macronucleus gets divided into two parts.
Some ciliates such as Paramecia are made with a mouth-like structure that is used to feed themselves and are known as oral grooves. The cilia push the food through the cytopharynx that acts as a gullet to the food vacuole. The food substrates break here. The ciliates that do not have an oral groove absorb the food and nutrients from the environment.
Ciliates use contractile vacuole to evacuate the excess water from the cell. Paramecia has posterior as well as anterior contractile vacuole. Whenever the water concentration goes high in the cell it gets moved to the contractile vacuole and is discharged out from there. This process is important for maintaining osmotic pressure as well as ionic balance. Also, the cells may burst due to an increase in water levels within the cell. With this process, the cell is also prevented from bursting.
There are two types of ciliates: parasitic and free living. The free-living ciliates stay out of the host body and hence are found anywhere in the environment. But parasitic ciliates live only inside the body of the host. An example of free-living ciliates is Paramecium that is found in freshwater bodies and survives on bacteria.
Balantidium coli that is responsible for causing dysentery in human beings is a parasitic ciliate and lives inside the body of human beings as endoparasites.
Then there are other ciliates such as Paraenchelys terricola and Apospathidium terricola that are found in soil. These types of ciliates are found in huge numbers in the soil which has a higher concentration of water.
Depending upon the water, nutrients, and other conditions of the environment, the concentration of ciliate differs from place to place.
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Ciliates reproduce both sexually (conjugation) and asexually (fission):
Two ciliates form a cytoplasmic bridge between them when they come in contact with each other. After this meiosis of micronuclei occurs which produces or creates haploid micronuclei. Some haploids might undergo disintegration happens. But some haploids get divided into two parts through mitosis in both the cells.
After this, one cell contacts the other cell with the help of a cytoplasmic bridge. At this moment it fuses with the micronuclei and forms a diploid nucleus. Thus when the cells separate a macronucleus is formed. After this fission process starts and forms two daughter cells. Every daughter cell has both types of cells namely micronucleus and macronucleus.
This stage of reproduction gets to see the two different processes. The mitosis that is forming of two diploid micronuclei happens with the micronucleus and the macronucleus gets divided into two parts. This cell is then divided into two daughter cells with micronucleus and macronucleus in every new cell.
Q1. Are Ciliates Harmful?
Ans. In general free-living ciliates are found in the environment. The parasitic form of ciliates is few in number in the environment. This is the only species found in the human body that causes diseases. Also, there are some parasitic ciliates found in fish that cause disease in fish and may be a matter of concern for aquaculturists. The ones found on invertebrates are commensals and parasites but do not pose any danger to the host or the environment. So barring some, ciliates cannot be termed as harmful.
Q2. How Many Nuclei Do Ciliates Have and What are their Functions?
Ans: Ciliates have two nuclei namely micronucleus and macronucleus. Both of them are vital for ciliate. Ciliates’ requirement for energy is very high and so they need a nucleus dedicated solely to control their metabolism and macronucleus is responsible for this function. Macronucleus also has genes that have the role of regulating cell functions. The other one is a smaller nucleus called micronucleus which is essential for reproduction.
Q3. What are Protists?
Ans: Protists are a group with diverse organisms in it. In general, they are unicellular (having only one cell), microscopic organisms, but there could be exceptions. Protists have a highly organized cell with a nucleus and organelles (specialized cellular machinery). Earlier simple organisms like single-celled algae and amoeba were part of the single taxonomy category of kingdom Protista but as better genetic information emerged scientists have become more clear about different groups within protists and their evolutionary relationships. All eukaryotes that are not animals, fungi, or plants belong to the protists group.