(Protos→ first/ primitive, Zoon→Animal)
Protozoa was first proposed by Gold fuss in the year 1817. However, protozoa were first studied by Antony van Leeuwenhoek in 1677. The scientific study of protozoa is called protozoology. Protozoans are called unicellular as well as a cellular organism.
On the structural basis, protozoan is called unicellular as it can be compared with a single cell of multicellular organisms but on the functional basis, it is called a cellular as it can be compared with the whole body of multicellular organisms i.e. all physiological processes are performed by a single cell.
Habit and Habitat:
Most of them are free living. Some are parasitic or commensal on symbiotic. Free-living protozoans are mostly aquatic. Some are found in damp soil.
They are unicellular, eukaryotic and microscopic. Their shape is variable. The body is covered with the cell membrane, pellicle, siliceous and calcareous shell.
Level of body organisation:
Their body organisation is molecular or protoplasmic.
They have bilateral or radial symmetry. Some are asymmetrical.
Mode of nutrition:
Nutrition is mainly holozoic. Some are parasitic.
Digestion is intracellular i.e. occurs inside the cell.
Locomotory organelles may be present or absent. If present they may be pseudopodia or cilia or flagella.
It occurs in through general body surface.
It also occurs general body surface.
It is carried out by one or more contractile vacuoles which are absent in parasitic and marine protozoans.
It is carried out by the asexual method and sexual method. Asexual method of binary fission, budding and sexual method like conjugation, syngamy i.e fusion of gametes.
It is the formation of protective covering(cyst) around the body during unfavourable condition for survival.
On the basis of locomotory organelles, phylum protozoa is divided into five different classes:
Class: Rhizopoda (Gr. Rhizo-root Podos-foot)
Class: Flagella/ Mastigophora:( Gr. Mastix- whip Phorrs- bearing)
Class: Cilia( Gr. Cilium- hair like ata- bearing)
Class: Sporozoa: (Gr. spora- spore zoon- animal)