Difference between Protozoans and Metazoans

The main difference between protozoans and metazoans is that protozoans are unicellular, whereas metazoans are multicellular. Protozoans are animal-like protists and are believed to be primitive types of animals. There is no division of labour as the single cell performs all the biological functions in protozoans. Metazoans are broadly divided into invertebrates and vertebrates. They have cells specialised into tissues and organs that show division of labour and perform specific functions. Both protozoans and metazoans are eukaryotic organisms and the cells lack a cell wall.

Difference between Protozoans and Metazoans

The table below shows the main differences between Protozoans and Metazoans.



They are unicellular

They are multicellular

They belong to the kingdom Protista

They belong to the kingdom Animalia

They are microscopic in size

They are macroscopic and generally can be seen by the naked eye

A single cell performs all the biological functions, such as respiration, digestion, osmoregulation, reproduction, etc.

There is a well-defined division of labour. Cells are specialised and are grouped into tissues, organs and organ system to perform various specialised functions

They reproduce by asexual and sexual methods

Sexual reproduction is the principle mode of reproduction in the majority of metazoans

They are believed to be primitive animals

They are believed to be evolved after protozoans

Examples are Amoeba, Paramoecium, Plasmodium, Entamoeba, etc.

Examples are flatworms, arthropods, birds, reptiles, mammals, etc.

What are Protozoans?

Protozoans belong to the kingdom Protista. Protozoans are unicellular eukaryotic organisms. They are either free-living or parasites. The cells lack a cell wall like metazoans or animals. A single cell performs all the different biological functions necessary for a living organism. They are believed to be primitive relatives of animals. They are heterotrophic. The mode of nutrition is holozoic. They ingest food by phagocytosis. The osmoregulation is performed by contractile vacuoles. They reproduce mainly by asexual means, some protozoans show sexual reproduction by conjugation or gametocyte formation.

They are categorised into four main classes, based on different locomotory structures present in them.

  1. Sarcodina or Amoeboids: The locomotory organ is pseudopodia. They use pseudopodia to capture their food. E.g. Amoeba, Entamoeba, etc.
  2. Mastigophora or Flagellates: They have flagella for locomotion. The body is covered by a pellicle. E.g. Trypanosoma, Trichomonas, Giardia, Leishmania, etc.
  3. Ciliophora or Ciliates: They have thousands of cilia present all over the body that help in movement, and also help in taking food-laden water inside the gullet. The body is covered by a pellicle. E.g. Paramoecium, Vorticella, etc.
  4. Sporozoa or Sporozoans: They lack a specialised structure for locomotion and are endoparasitic. E.g. Plasmodium, Myxidium, Globidium, etc.

What are Metazoans?

Metazoans or animals are eukaryotic multicellular organisms. They belong to the kingdom Animalia. Metazoans are mostly bilaterally symmetrical. They show division of labour. Lower invertebrates have tissue or organ level of body organisation, whereas higher invertebrates and vertebrates have organ-system level of body organisation. Animal cells lack a cell wall like protozoans. The complexity increases as we move from invertebrates to vertebrates. Metazoans include insects, worms, jellyfish, octopus, molluscs, birds, fish, amphibians, reptiles and mammals, etc.

The bilateral metazoans can be broadly categorised into protostomes and deuterostomes on the basis of differences in embryological development.

  • Protostomes: The blastopore develops into the mouth. Most invertebrates are protostomes. E.g. nematodes, arthropods, flatworms, annelids and molluscs.
  • Deuterostomes: The blastopore develops into the anus. Echinoderms and chordates are deuterostomes.

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