PROTOZOA
Definition
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Unicellular
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Eukaryotic
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Lack of cell wall
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Non-phototrophic
Introduction
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Present in the Pre-Cambrian era.
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Based on the mode of nutrition, protozoa are of the following two types:
~ Free-living protozoa:
They ingest particulates, such as bacteria, yeast and algae.
~ Parasitic protozoa:
They derive nutrients from the body fluids of their hosts.
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In a series of classifications proposed by Cavalier-Smith and his collaborators during 1993, protozoa have been ranked as a kingdom.
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Anton van Leeuwenhoek was the first person to see protozoa, using microscope he constructed with simple lenses.
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Classification
The classification of protozoa is mainly based on their means of locomotion. They are subdivided into the following four classes.
1.
Amoeboids:
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Motility is due to the streaming of ectoplasm
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This is known as pseudopodia (false feet).
2.
Flagellates:
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Locomotion is effected by one or more whip-like, thin structures
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This is known as flagella.
3.
Ciliates:
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Locomotion is carried out by means of short hair-like projections
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This is known as cilia.
4.
Sporozoa:
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Members of the class sporozoa do not have locomotor organelles in their mature stage.
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However, immature forms exhibit some type of movement.
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All the members of this group are parasites.
Classification
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Do not have a cell wall; however, some of them possess a flexible layer, a pellicle, or a rigid shell of inorganic materials outside the cell membrane.
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Have the ability to move by locomotor organelles or by a gliding mechanism during their entire life cycle.
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Have heterotrophic mode of nutrition, whereby the free-living forms ingest particulates, such as bacteria, yeast and algae, while the parasitic forms derive nutrients from the body fluids of their hosts.
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Reproduce primarily by asexual means, although in some groups sexual modes also occur.
Common Examples:
Amoeba
Euglena
Paramecium
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Chlamydomonas
Ecology (habitat)
Protozoa are ubiquitous (found everywhere).
They are present in all aquatic or moist environments, and their cysts can be found in even the most inhospitable parts of the biosphere.