Protozoans and its classification

• The word Protozoa is derived from two Greek words: protos means first; zoon means animal.
• They are the first animals with a protoplasmic grade of body organization.
• They are simple, unicellular microscopic organisms which may be solitary or colonial.
• All the vital activities are performed by a single cell so no physiological divison of labour occurs.
• The body is naked or covered by pellicle and in some cases may be exoskeleton or internal skeleton present.
• Various kinds of locomotory organs are present such as pseudopodia in Sarcodina, whip-like flagella in Flagellate and hair-like cilia in ciliate and locomotory organs absent in case of sporozoa.
• The protoplasm is divided as outer ectoplasm and inner endoplasm.
• Nutrition is holophytic (plant-like), holozoic (animal) or parasitic.
• Digestion is intracellular and occurs inside food vacuoles.
• Respiration occurs through the general body surface by diffusion.
• Excretion occurs through general body surface, a temporary opening in the ectoplasm or through the permanent pore called the cytopyge, or contractile vacuoles.
• Reproduction is sexually or asexually.
• Sexual reproduction by conjugation of adults or by fusion of gametes.
• Life cycle is often complicated with alternation of generation.
• Formation of resistant cysts occurs to overcome unfavourable conditions as well as to help in dispersal.

They are diverse group of organisms with four sub-phylum. They are:

A) Sub-phylum: Sarcomastigophora

• It is characterized by the presence of both flagella or pseudopodia for locomotion.
• They possess only one type of nucleus.
• There is no spore formation.
• Sexual reproduction occurs by syngamy.
• It is classified into three super classes: Mastigophora, Opalinata and Sarcodina.
• e.g.,Euglena, Ceratium, Chilomonas, etc.

B) Sub-phylum: Sporozoa

• Locomotory organs are absent in adult stage.
• All are parasitic forms.
• Cilia or flagella may be present in gametes.
• Sexual reproduction occurs by syngamy.
• The spores are simple and contain one to many sporozoites.
• The sporozoites are the infective phase.
• The nucleus is of only one type.
• It is classified into three classes: Telosporea, Toxoplasmea and Halosporea.
• e.g., Plasmodium, Nematocystis, Caelosporidium, etc.

C) Sub-phylum: Cnidospora

• Al members are parasitic in cold- blooded vertebrates and in invertebrates.
• Spores are multicellular.
• Zygote gives rise to one or more trophozoids– without sporogony.
• It includes two classes: Myxosporidea and Microsporidea.
• e.g.,Ceratomyxa, Nosema, etc.

                                                                                   Image source: biologynotes

D) Sub-phylum: Ciliophora

• They have rows of cilia, the unique nuclear dimorphism i.e. two types of nuclei are present: macronucleus and micronucleus.
• Most ciliates possess a cell mouth or cytostome.
• It includes only one class: Ciliata.
• e.g.,Paramecium, Coleps, Colpedium, etc.

References:

i) https://www.microscopemaster.com/protozoa.html

ii) https://www.onlinebiologynotes.com/phylum-protozoa-general-characteristic-classification/

Protozoans and its classification