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Phylum I: Protozoa (Unicellular Protist Animals)

Protozoans (Latin: protos meaning first, zoon meaning animal) are single-celled animals which may be free living or parasitic where a single cell performs all the functions of the body they are found in fresh water, sea water, and moist soil.

General Characteristics
  1. Minute, acellular or unicellular microscopic animals; uni- or multinucleate.
  2. They may be solitary, colonial, free-living, parasitic or symbiotic.
  3. No organs except cell organelles are present.
  4. Locomotion by pseudopodia, flagella or cilia.
  5. Mode of nutrition variable: it may be holozoic, holophytic, saprophytic, caprozoic or parasitic.
About 30,000 species are known.

Amoeba, Monocystis, Entamoeba, (cause amoebic dysentery), Euglena, Paramecium, Opalina, Vorticella, Trypanosoma (causes sleeping sickness), and Plasmodium (causes malaria).

Economic Importance of Protozoa

Many protozoans are neither harmful nor beneficial for man. Some types however play significant roles in the formation of soils and earth deposits, such as chalk and rock formed by Radiolaria and Foraminifera. Certain shelled forms when they die, form an ooze at the bottom of the ocean that may solidify into rocky formations. 

The cellulose eaten by termites is digested in their intestines by certain flagellated protozoans, thus changing it into a form that is usable by termites.

(a) Amoeba

(b) Entamoeba

(c) Notiluca

(d) Opalina

(e) Euglena

(f) Paramecium

(g) Stenter

(h) Trypanosoma

Examples of phylum Protozoa

Protozoan Parasites of Man

Many harmless types of protozoans live in the intestines of animals and man. However, some parasitic protozoans are pathogenic causing various diseases in man. Some of these are Trypanasoma gambiense causing 'sleeping sickness', Entamoeba histolytica, causing amoebic dysentery, and several types of malaria are caused by different species of Plasmodium.

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