The kingdom Protista includes unicellular, eukaryotic organisms. They include both photosynthetic and non-photosynthetic forms. The kingdom Protista includes protistan algae, slime moulds and protozoans.
(1) Protistan algae : They are photosynthetic protists. They include dinoflagellates and diatoms.
(a) Dinoflagellates : These are golden brown biflagellated photosynthetic protists. They possess cellulose wall in the form of distinct interlocking plates. Some dinoflagellates glow and make the water look red to cause ‘red tide’, e.g., Gonyaulax.
(b) Diatoms : They are group of golden brown photosynthetic protists which are covered by two valved silicious wall called shell or frustule. They pile up at the bottom water reservoirs and form big heap called diatomite.
(2) Slime moulds : Slime moulds are both plants and animals like. They are plant like in the production of spores, and animal like in the mode of nutrition and somatic organisation. It moves freely on the substratum and feeds on bacteria, fungal and algal spores and also absorb nutrients directly from the substratum.
(3) Protozoa : These are microscopic unicellular organisms with varied shapes and forms. This may be free living, commensal or parasitic. They lack cell wall, but some possess proteinaceous flexible pellicle, locomotion occurs by pseudopodia, flagella or cilia. These reproduce asexually by binary fission, Some reproduce sexually by conjugation.