54. Subkinngdom Protozoa. Phylum Ciliophora. Balantidium coli.

Phylum Ciliophora. Balantidium coli

Phylum Ciliophora (also known as Ciliata)

• Members of this phylum are unicellular protozoa that are typically larger and more structurally complex than other protozoans.
• Some ciliates can reach sizes up to 2 millimeters, making them visible to the naked eye in certain cases.
• They inhabit a variety of aquatic environments, including:
• Freshwater ecosystems such as lakes and ponds
• Marine habitats such as oceans and estuaries
• Moist terrestrial environments such as damp soils
• Ciliates can live as:
• Free-living organisms
• Ectosymbionts that live on the surfaces of other organisms
• Endosymbionts that reside within other organisms
• Parasites, although parasitic forms are less common in this phylum

Key Structural Features of Ciliophora

• A defining feature of ciliates is the presence of cilia, which are:
• Short, hair-like projections covering all or part of the cell surface
• Used for movement, feeding, attachment, and sensation
• Structurally similar to flagella, but present in greater numbers and shorter in length
• Ciliates have two types of nuclei:
• A micronucleus, which is small and diploid, involved in genetic exchange and reproduction
• A macronucleus, which is large and polyploid, responsible for metabolic and developmental control
• The cell also contains:
• A cytostome, which acts as a cell mouth for food intake
• A cytopharynx, which channels food particles
• Digestive vacuoles for intracellular digestion
• Contractile vacuoles for expelling excess water
• A cytoproct, which functions as the cell’s waste exit

Reproductive Processes in Ciliophora

• Asexual reproduction takes place through binary fission, where the organism divides into two genetically identical cells.
• Sexual reproduction occurs via a process called conjugation, which involves:
• Two compatible ciliates joining temporarily
• The exchange and fusion of haploid micronuclei
• This process increases genetic diversity but does not immediately result in new offspring

Balantidium coli

• Balantidium coli is the only known ciliate that infects humans and causes disease.
• It primarily inhabits the caecum and colon of humans and certain animals including pigs, rats, and other mammals.
• This organism is more commonly found in animals than in humans, and pigs are considered the primary reservoir.

Forms of Balantidium coli

• The organism exists in two forms during its life cycle:
• The trophozoite, which is the active, feeding form
• Trophozoites are relatively large, measuring approximately 70 by 45 micrometers, but can grow up to 200 micrometers
• The cyst, which is the dormant and infective stage
• The cyst is characterized by a resistant wall, and it contains structures such as a macronucleus, micronucleus, contractile vacuole, and cilia