* Mention the distinguishing features of phylum
protozoa and give an outline classification
of the same with characters and examples of
its subclasses.
Answers
Answer:
There are about 50,000 known species of Phylum Protozoa.
Protozoans exhibit mainly two forms of life; free-living (aquatic, freshwater, seawater) and parasitic (ectoparasites or endoparasites). They are also commensal in habitat.
They are small, usually microscopic, not visualize without a microscope.
They are the simplest and primitive of all animals.
They have a simple body organization. i.e. with a protoplasmic grade of organization.
The body is unicellular (without tissue and organs).
They have one or more nuclei which are monomorphic or dimorphic.
Body naked or bounded by a pellicle, but in some forms may be covered with shells and often provided with an internal skeleton.
They are solitary (existing alone/single) or colonial (individuals are alike and independent).
Body shape variables may be spherical, oval, elongated or flattened.
Body symmetry either none or bilateral or radial or spherical.
Body form usually constant, varied in some, while changing with environment or age in many.
Body protoplasm is differentiated into an outer ectoplasm and inner endoplasm.
The single-cell body performs all the essential and vital activities, which characterize the animal body; hence only subcellular physiological division of labor.
Locomotory organs are fingers like pseudopodia, whip-like flagella, hair-like cilia or none.
Nutrition may be holozoic (animal-like), holophytic (plant-like), saprozoic or parasitic.
Digestion occurs intracellularly which takes place inside the food vacuoles.
Respiration occurs by diffusion through the general body surface.
Excretion occurs through the general body surface, but in some forms through a temporary opening in the ectoplasm or through a permanent pore called cytopyge.
Contractile vacuoles perform osmoregulation in freshwater forms and also help in removing excretory products.
Reproduction asexual (binary or multiple fission, budding, sporulation) or sexual (conjugation (hologamy), game formation (syngamy)).
The life cycle often complicated with alternation of asexual and sexual phases (alternation of generation).
Encystment commonly occurs to resist unfavorable conditions of food, temperature, and moisture, and also helps in dispersal.
The single-celled individual not differentiated into somatoplasm and germplasm; therefore, exempt from natural death which is the price paid for the body.
Protozoans exhibit mainly two forms of life; free-living (aquatic, freshwater, seawater) and parasitic (ectoparasites or endoparasites). They are also commensal in habitat.
Examples: Euglena, Amoeba, Plasmodium, Paramecium, Podophyra, etc.