Introduction to phylum protozoa
The phylum protozoa consist of about 15,000 species of protozoans. The phylum consists of microscopic organisms in which all the vital activities are performs by single cell, commonly referred as single celled organisms. They are cosmopolitan in distribution and includes aquatic (fresh water and marine) forms too.
Phylum protozoa includes free living animals like Euglena, Paramecium, Amoeba, Noctiluca and Elphidium and parasitic animals like Plasmodium species, Monocystic, Entamoeba, Trypanosoma and Giardia.
The organisms of this phylum greatly vary in shape, size, locomotory organelles, and method of reproduction.
The protoplasmic unit consist of protozoan consists of nucleus and cytoplasm. The cytoplasm is divisible into outer homogenous ectoplasm and inner heterogenous endoplasm.
Ectoplasm is involved in procurement of food, respiration, excretion of waste products, and locomotion. Different types of locomotory organs are found in protozoans are whip like flagella (flagellates), hair like cilia (ciliates), and foot like pseudopodia (sarcodines).
Endoplasm surrounds the nucleus and contains trapped undigested food vacuoles and cell organelles (Golgi apparatus, mitochondria, and endoplasmic reticulum). Other structures that can be seen are contractile vacuole and kinetoplast.
Reproduction in protozoans may be through simple binary fission or through syngamy.
Protozoans exists generally in two morphologic forms namely, trophozoite form (an active, vegetative stage, and feeding stage) and cyst from (an dormant or inactive stage, infective stage). A protozoan enters into the dormant form during the time deficiency of food supply or due to change of environment.
E.g. Amoeba, E. coli, Giardia lambia, Trichomonas hominis, Chilomastix mesnili, Trichomonas tenax, Trichomonas vaginalis, Entamoeba histolytica, Endolimax nana, Iodamoeba butschilii, Dientamoeba fragilis, Entamoeba gingivalis, Plasmodium species, Pneumocystis carinii, etc
Classification of Phylum Protozoa
Phylum protozoa is divided into 4 classes.
- Class I: Rhizopoda or Sarcodina: Locomotory organelles are pseudopodia, body shape changeable. E.g. Amoeba
- Class II: Mastigophora or Flagellata: Locomotion is through one or more thread-like flagella. E.g. Euglena
- Class III: Sporozoa: All are parasitic forms, locomotory organelles and contractile vacoule are absent, complex life history. E.g. Plasmodium
- Class IV: Cilliata: Locomotion is by cilia, contains two or more nuclei. E.g. Paramecium
