Protozoa are single-celled eukaryotic organisms that were first discovered by Anton van Leeuwenhoek in the 17th century. They exhibit a variety of life forms including free-living, symbiotic, commensal, and parasitic. Protozoa are microscopic in size, ranging from 0.002 mm to 16 mm. They have primitive cellular organization and perform all life activities within a single cell. Reproduction can occur asexually through binary fission or multiple fission, or sexually through conjugation of gametes.

1. PHYLUM-PROTOZOA
ASHOK KUMAR BOLLAPALLI
M.Sc.,B.Ed.,CSIR-NET.,MA(Lit)
Lecturer in Zoology
KRK Govt Degree & PG College
ADDANKI-523201, Prakasam District
@9652929696,9441635264
ashokkumarzoology@gmail.com

2. INTRODUCTION
• These organisms were first discovered by Anton
Van Leuven Hoek(1632-1723)
• It includes free and parasitic forms
• Some live in soil and most in fresh water
• Goldfus in 1820 named them as PROTOZOA
• Protos= First; Zoan= Animal
• The morphological structure was defined by Von
Sie Bold in 1845. He identified them as single
celled organisms
• Dobell called them as acellular

3. SPECIAL CHARACTERS
1. Division of labour is found among organelles
which are intracellular
2. Cell division (Mitosis) of metazoans is exhibited
in asexual reproduction
3. All the life activities are carried out by single cell
4. Response to stimulii can be correlated to the
biginning of nervous system
5. Conjugants in Paramecium indicates the
beginning of sexual dimorphism

4. General Characters
Microscopic, primitive animalcules
Acelluar or single celled animals with protoplasmic
grade of organisation
Solitary or colonial forms, free living symbionts,
commensals or parasites
Distributed all over the world in water, soil, air, on
animals, and inside the animals
Round, spherical, flat in shape
Symmetry is either bilateral or radial or spherical or
asymmetric

5. General Characters contd..
 Size varies from 0.002 mm to 16mm, a fossil Nummulite
is large and measured about 19 cm
Body- Naked/pellicle/shells- Shells are made up of
mucus/ cellulose/ organic, inorganic material and sand
particles
All life activities are performed by single cell. Various cell
organelles are responsible for different activities
Cell membrane may be thin or thick, may have lines,
fibres and myonemes
Myonemes are useful for contraction and expansion and
also for supporting . Microvilli are useful for transport of
food material.

6. General Characters contd..
Locomotion is by pseudopodia, flagella, cilia. These
help in capturing food material
Cell contains one or two or more nucleii. Macro
nucleus is for metabolic activities and micronucleus is
for reproduction
These are phytotrophic, holozoic, holophytic,
saprophytic, saprozoic or parasitic.
Respiration is by simple diffusion. Parasites are
anerobes
Excretion is by general body surface/contractile
vacuoles-osmoregulation too. Marine and parasitic
organisms lack contractile vacuoles.

7. General Characters contd..
Reproduction is by asexual or sexual
Asexual reproduction is by binary fission/
multiple fission/plasmotomy- cytoplasmic
division to form two or more multicellular
daughter cells
Sexual reproduction is by conjugation or fusion of
gametes
These originated in precambrian of paleozoic era.
Nearly 30,000 protozoans are recognised so far.