11th Class Biology Biological Classification And System Of Classification / जैविक वर्गीकरण और वर्गीकरण की प्रणाली Protozoan Protists (Gr. Protos = first ; zoon = animal)

It include all unicellular (or acellular) eukaryotic animals. These are most primitive organisms considered as animals because of heterotrophic nutrition and motility. About 50,000 species (30,000 present and 20,000 extinct) are so far known.

Brief history : Protozoans were first studied by Leeuwenhoek (1677). The name “Protozoa” was coined by Goldfuss (1817). The branch of their study is called Protozoology.

General characters

(1) Protozoans are the simple and primitive organisms.

(2) They are free living or parasitic.

(3) All the free living forms are aquatic.

(4) They are asymmetrical or radially symmetrical or bilaterally symmetrical.

(5) They are unicellular (acellular).

(6) They have protoplasmic grade of organization.

(7) Locomotion is effected by flagella, cilia or pseudopodia.

(8) Nutrition is holophytic, holozoic, saprozoic or parasitic.

(9) Digestion is intracellular.

(10) Excretion and respiration occurs by diffusion.

(11) In fresh water protozoans osmoregulation is carried out by the contractile vacuoles.

(12) Encystment is a common phenomenon.

(13) Reproduction occurs by asexual and sexual methods.

Classification of Protozoans

Protozoans are classified on the basis of locomotory organelles into following classes.

Class 1. Rhizopoda or Sarcodina

(1) There is no definite cell wall or pellicle.

(2) There is no definite shape.

(3) The locomotory organs are pseudopodia.

(4) There is no permanent mouth or anus.

(5) The contractile vacuoles are present in the fresh water forms.

The rhizopoda has been divided into five orders. They are as Lobosa, Filosa, Foraminifera, Heliozoa and Radiolaria.

Examples : Amoeba, Entamoeba histolytica, Entamoeba coli, Pelomyxa, Globigerina, Actinophryx.

• In Arcella has an exoskeleton of tactin.
• Giardia is called ‘Grand old man of intestine’.
• Actinophryx is called ‘Sun animalcule’ as it resemble the sun.

Class 2. Flagellata or Mastigophora

(1) The body is covered by a thin pellicle or cuticle.

(2) The locomotory organs are flagella.

(3) The contractile vacuoles are present in fresh water forms with accessory vacuoles.

(4) Chloroplast are found in some forms.

(5) They may be free living or parasitic.

The class flagellata has been divided into eight orders. They are as Chrysomonadina, Cryptomonadina, Euglenoidea,  Phytomonadina, Dinoflagellata, Cystoflagellata, Protomonadina and Polymastigina.

Examples : Chrysamoeba, Cryptomonas, Volvox, Chlamydomonas, Noctiluca, Mastigamoeba, Monal, Bado, Trypanosoma, Leishmania, Proterospongia etc.

• Trychonymph (symbiotic) live in alimentary canal of termite that is digest to cellulose.
• Noctiluca shows bioluminiscense due to luciferin protein. It is also called the ‘Fire of sea’.

Class 3. Sporozoa

(1) They are exclusively endoparasitic.

(2) The body is covered by pellicle.

(3) Reproduction takes place by spore formation.

The class is divided into two sub-classes, namely, Telosporidia and Neosporidia.

Sub-class (i) Telosporidia

(1) The spores do not contain polar capsules or filaments.

(2) The life history ends with the formation of spores.

(3) The spore cases are simple and contain many spores.

Examples : Monocystis, Gregarina, Isopora, Eimeria, Plasmodium, Babesia etc.

• Babesia causes the ‘Taxas cattle fever’ in animals. This disease also called ‘Red water fever’ or Haemoglobin uric fever.
• Monocystis is found in seminal vesicle of earthworm, and causes sterlity in earthworm. It is monogenetic in nature.
• Eimeria is found in epithelial cells of liver of Rabbit.

Sub class (ii) Neosporidia

(1) The trophozoite is amoeboid multinucleated.

(2) Spore cases are complex usually having a single germ.

Examples : Nosema, Myxidium, Globidium etc.

Class 4. Ciliophora

(1) The body is covered by thin pellicle.

(2) They have a fixed permanent shape.

(3) The locomotory organs are cilia.

(4) Tentacles are present.

The class ciliophora is divided into two sub-classes, namely Ciliata and Suctoria.

Sub-class (i) Ciliata

(1) Cilia are present throughout life.

(2) Tentacles are absent.

(3) Mouth and cytopharynx are usually present. Cytopyge is a temporary anal apperture.

(4) Contractile vacuoles are present.

(5) Trichocysts, organs of offense and defence are present in certain forms.

Examples : Paramecium, Stylonchia Vorticella etc.

• Vorticella is called ‘Bell animalcule’. It is a pedicellate protozoan.
• Nyctotherus is a parasite in the rectum of frog. It is also found in the rectum of cockroach.

Sub-class (ii) Suctoria

(1) Cilia are present only in the young conditions and adults are devoid of them.

(2) Tentacles are present in the adult.

(3) One to many contractile vaculoes are present.

Examples : Acineta, Dendrocometes, Dendrosoma etc.