GENERAL CHARACTERISTICS OF PROTOZOA
Proto=Primitive/First/early; Zoon=Animals
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Hence, Protozoans are the primitive types of animals,
which are believed to be evolved first in the earth surface.
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Earlier protozoans are included under animal kingdom,
but now a days it is included under kingdom protista. This
is because, protozoa are unicellular eukaryotes.
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They live in wide varieties of moist habitats such as fresh
water, marine environment and may be in moist soil.
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They may be parasitic or commensial, symbiotic or free
living, sessile or motile and mostly solitary and some are
colonial.
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Protoplasmic grade of body organization.
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Germ layers are absent.
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Body is naked or covered by a pellicle or may be covered
by an exoskeleton made up of shell/test/cyst/theca.
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Almost all types of symmetry are found, i.e-bilateral,
radial, spherical and may be no symmetry(asymmetry).
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Coelom is absent.
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Locomotary organelles may be finger like pseudopodia,
hair like cilia or whip like flagella. Some species do not
have any locomotary organelles.
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Division of labor is restricted to organelles.
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Nuclei may be monomorphic or dimorphic.
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Nutrition may be holozoic, saprozoic or parasitic.
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Respiration takes place through general body surface.
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Digestion occurs inside the food vacuole. Mouth and anus
absent.
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Excretion by general body surface or by the help of
contractile vacuole. In some forms temporary or
permanent opening called cytopyge are found in the body
surface.
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Intracellular circulation or cyclosis occurs.
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Nervous system is absent but a neuromotor system may
be present.
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Asexual reproduction occurs by simple fission, budding
and cyst formation. Sexual reproduction if occur then by
conjugation or by syngamy.
