THE FLAGELLATED PROTOZOA
1. Flagellated protozoan possess flagella for locomotion. The flagellapush or pull the protozoans through aquatic medium. Flagella may produce two-dimension: Whip like movements and helical movements.
2. Current molecular data suggest that the flagellates are the ancestors of the amoeboid species.
3. Flagellates possess pellicle. It gives them definite shape.
4. Most species ace fee living and motile.
5. Flagellates have more than 7500 describe species. Flagellates are distributed in many Flagellated protozoan have two groups: Phytoflagellated (photosynthesizing) protozoan and Zoollagellated (particle feeding and parasitic) protozoan.
(a) Phytoflagellated Protozoa
The phytollagellates possess chlorophyll and one or two flagella. They produce a large portion of the food in marine food webs. They also provide oxygen to marine animals. Marine phytoflagellates include Dinoflagellates. Dinoflagellates have following characteristics:
1. Flagella: Dinollagellates have two flagella. One flagellum wraps around the organism in a transverse groove. Organism spins on its axis due to primary action of this flagellum. A second flagellum is a trailing flagellum. It pushes the organism forward.
2. Pigments: They possess pigments chlorophyll. Many dinollagellates contain xanthophylls pigments. It gives them a golden colour.
3. Toxins: Several genera like Gymmnodinium produce toxins. Periodic blooms of these organisms are called red titles. It kills fish kills. Humans who consume tainted molluscs or fish may die. According to Bible first plague as Moses. It visited upon Egyptians. It was a blood-red tide. It killed fish and fouled water. Red Sea is named after these toxic dinoflagellate blooms.
It is a freshmater phytotlagellate It has following characteristics:
1. Nutrition: Each chloroplast has a pyrenoid. It synthesizes and stores polysaccharides. Euglenoids feed by absorption in darkness and lose their green color. Some euglenoids lack chloroplasts. So these are heterotrophic.
2. Stigma:Fuglena orients toward light of certain intensities.
A pigment shield (stigma) covers a photoreceptor at the base of the flagellum. It allows light to strike the photoreceptor from only one direction. Thus Euglena orients and moves in relation to a light source.
3. Euglenoid flagellates are haploid They reproduce by longitudinal binary fission. Sexual reproduction is absent.
(b) Zooflagellated Protozoa
Zoollauellates lack chloroplasts. So they are heterotrophic. Some members of this class are important parasites of humans. Its example is Trypansoma.
This species is divided into three subspecies. T.b.bruccei, T.b.gambiense and T.b.rhodesiense. These are collectively called Trvpanosoma brucei complex. The first species is a parasite of nonhuman mammals of Africa.The latter two cause sleeping sickness in humans. Tsetse flies (Glossina spp.) are intermediate hosts and vectors of all three subspecies.
Fig: Life cycle of Tranpanosoma: (a) Transmission by teste fly (b) Structure
1. Cycle in fly:A tsetse fly bites an infected human or mammal. It sucks blood and picks up parasites. Trypanosomes multiply asexually in the gut of the fly for about 10 days. Then they migrate to the saliva glands. Then trypanosomes forms a number of body forms in 15 to 35 days.
2. Cycle in vertebrate host: Then the infected tsetse fly bites another vertebrate host. The parasites travel with salivary secretions into the blood of a new definitive host. • The parasites multiply asexually in the new host. It again transform through a number of body forms.
3. Disease cycle: Parasites live in the blood lymph, spleen, central nervous system, and cerebrospinal fluid. Some trypanosomes enter the central nervous system. They cause general apathy, mental dullness, and lack of coordination. Sleepiness develops in the host. The infected individual may fall asleep during normal daytime activities. It may cause death due to previous symptoms, heart failure, malnuirition and other weakened conditions. Sleeping sickness is curable at early stages. But recovery is impossible advanced infection of central nervous system.
Fig: Different pseudopodia: (a) Lobopodia (b) Filopodia (c) Reticulopodia (d) Axopodia