Biology Sikshya

           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.

• Earlier protozoans are included under animal kingdom,

       but now a days it is included under kingdom protista. This
       is because, protozoa are unicellular eukaryotes.

• They live in wide varieties of moist habitats such as fresh

       water, marine environment and may be in moist soil.

• 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.

• Germ layers are absent.

• Body is naked or covered by a pellicle or may be covered

       by an exoskeleton made up of shell/test/cyst/theca.

• Almost all types of symmetry are found, i.e-bilateral,

       radial, spherical and may be no symmetry(asymmetry).

• Coelom is absent.

• Locomotary organelles may be finger like pseudopodia,

       hair like cilia or whip like flagella. Some species do not
       have any locomotary organelles.

• Division of labor is restricted to organelles.

• Nuclei may be monomorphic  or dimorphic. 

• Nutrition may be holozoic, saprozoic or parasitic.

• Respiration takes place through general body surface.

• Digestion occurs inside the food vacuole. Mouth and anus

       absent.

• 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.

• Intracellular circulation or cyclosis occurs.

• Nervous system is absent but a neuromotor system may

       be present.

• Asexual reproduction occurs by simple fission, budding

       and cyst formation. Sexual reproduction if occur then by
       conjugation or by syngamy.