Protozoan Taxonomy & Classification

PROTOZOAN TAXONOMY

Zoologists who specialize in the study of protozoa are called proto-zoologists. The protests base diversity of ultrastructure, life cycle, mitochondria, DNA sequence data, life styles and evolutionary lineages. Therefore, they cannot be put in a single kingdom. Thus classification scheme of protozoan have been changed. New evidences have been collected from electron microscopy, genetics. biochemistry and molecular biology^–. These evidences shows that phylum protozoa has itself may phyla. Therefore, protozoa have been given the status of kingdom. Number of species of protozoan are 64,000. Most of these are fossils.

Recent Protozoan Classification

Kingdom Protozoa: Single-celled eukaryote. lacking collagen and cell walls. It has following phylums:

1. Phylum Chlorophyta: Unicellular and multicellular, photosynthetic pigments present: Reserve food material is starch: biflagellated stages present: free living autotrophs: some are heterotrophic. Examples: Chlamydomonas, volvox.

The Discicristates: This is an informal group. This group possess disc-shaped mitochondria, cristae.

2. Phylum Atostlata: They contain an axostyle which is made of microtubules. This phylum has single class.

Class Parabaselea: They contain large Golgi bodies associated with karymastigont: thousands of flagella present: mostly symbiotic: living in host ranging from human to termites to wood roaches. .

Order Trichomonadida: Some kinetosomes associated with rootlet filaments; parabasal body present: no sexual reproduction: all parasites. Examples: Dientamoeba, Trichomonas                                             

3. Phylum Euglenozoa: Cortical microtubules are present; flagella are present; mitochondria with discoid nuclei: nucleoli present during mitosis.

(a) Subphylum Euglenida: Contain pellicular microtubules that stiffens the pellicle. Mostly found in freshwater habitat and are photosynthetic.

Class Euglenoidea: Two flagella with different structures; some species with light sensitive pigments and chloroplast. Example: Euglena

(b)  Subphylum Kinetoplasta: Mitochondria contain a disc of DNA. Class : Trypansomatidea: One or two flagella present: single mitochondria: Golgi bodies present; all parasites. Examples: Leishmania. Trypansoma

4. Phylum Retortamonada: Lack Golgi bodies and mitochondria; three anterior and one posterior flagellum; free living or parasitic. All members have a prominent body of massed DNA within the mitochondrion called kinetoplast.

Class Diplomonadea: One or two kinetosomes with a nucleus (a karyomastigont): individual karyomatigonts with one to four flagella; cysts present: parasitic or free living.

Order Diplomonadida: Two karyomastigonts each with four flagella: a variety of microtubular bands;Examples: Giardia, Entermonas, Spironucleus, Trigonomas.

The Alveolata: All members in this informal heading possess flattened membranous sacs (alveoli) underneath the plasma membrane. The mitochondrial cristae are tubular.

5. Phylum Apicomplexa (formerly sporozoa): Contain an apical complex used to penetrate host cells; cilia and flagella absent in adults but present in certain reproductive stages;cysts often present;all parasitic.

(i) Class Gregarinea: Gametes are similar in size and shape: zygotes forming oocvsts with gametocysts; they are parasites in body cavities or digestive tract in invertebrates. Examples: Gregarina, Monosystis

(ii)   Class Coccidea: Mature gamonts intracellular: most species live inside the vertebrates. Examples: Babesia, Cyclospora, Cryptospordidium, Emeria, Toxoplasma, plasmodium.

6. Phylum Ciliophora: Cilia present; two types of nuclei: binary fission and sexual reproduction present. Examples: Balantidium. Paramecium. Stentor, Tetrahyymena,  Trichodina, Vorticella

7. Phylum Dinozoa (formerly dinoflagellata): Two flagella present: chlorophylls present free living or parasitic, planktonic. or mutualistic. Examples: Noticiluca, Zooxanthella, Peridinium,Ceratium, Gymodinium.

Ameobozoans: It is an informal heading because these members do not form monophyletic group. All members moves by pseudopodia; asexual reproduction by fission ; most free living; some species are obligate pathogens of human and mammals: all have branching tubular mitochondrial cristae. There is not flagellate stage in their life cycle.

Rhizopodans: locomotion by lobopodia, filopodia or protoplasmic flow. Examples: Amoeba proteus, Entamoeba, Diffugia, Arcella

The  Cercozoa: This is an informal heading. This is very diverse group. It is defined exclusively by Molecular characteristics. It includes nonphotosynthetic amoebae, amonoflagellates and very large number of zooflagellates in soil and freshwater. All have tubular mitochondria! cristae.

8. Phylum Granuloreticulosa: They move by reticulopodia secrete calcium carbonate tests;. pseudopodia protrude through numerous pores.

Class Foraminifera: It includes foraminiferans; some species form symbiotic association with algae. These have an extensive fossil record. Examples: Globogernia, Vetebranlia.

9. Phylum Radiozoa: All members possess radiating microtubular supports called axopodia. They move by these axopodia. It includes radiolarians. Examples: Actinophyrys. Clatrulina

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