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Protists are of different types:
(i) Plant like protists (Photosynthetic protists):
(a) They are termed as phytoplanktons, also known as Chrysophytes.
(b) They are autotrophic (photosynthetic) in nature and form major producers of ocean ecosystem.
(c)Most of them are referred as Diatoms because they have body wall made up of two soap-box like fitting silica covers. E.g. Diatoms.
1. Dinoflagellates:
(i) They are aquatic (mostly marine) and autotrophic (photosynthetic).
(ii) They have wide range of photosynthetic pigments which can be yellow, green, brown, blue and red.
(iii) The cell wall is made up of cellulosic stiff plates.
(iv) A pair of flagella is present, hence they are motile.
(v) They are responsible for famous ‘red tide’. E.g. Gonyaulax. It makes sea appear red.
2. Euglenoids:
(i) They lack cell wall but have a tough covering of proteinaceous pellicle.
(ii) Pellicle covering provides flexibility and contractibility to Euglena.
(iii) They possess two flagella, one short and other long.
(iv) They behave as heterotrophs in absence of light but possess pigments, similar to that of higher plants, for photosynthesis.
(ii) Animal like protists (Consumer protists):
(a) They are the primitive animal forms.
(b) They are also termed as protozoans.
(c) These are heterotrophic and lack cell wall.
(d) Amoeboid protozoans have pseudopodia as locomotory organs. E.g. Amoeba, Entamoeba.
Amoeba is free living form, but Entamoeba is endoparasite and causes amoebic dysentery.
(e) Flagellated protozoans have flagella as locomotory organ. E.g. Trypanosoma.
(f) Cilliated protozoans have cilia for locomotion. E.g. Paramoecium.
(g) Plasmodium is a Sporozoan protozoa. It causes malaria. It forms spores in one of its life stages.
(iii) Fungi like protists (Consumer decomposer protists):
(a) They form a group called Myxomycetes.
(b) They are saprophytic in nature, found on decaying leaves.
(c) Their cells aggregate to form a large cell mass called plasmodium.
(d) The spores of plasmodium are very tough and survive extreme conditions, e.g. Slime molds.