Division CHRYSOPHYTA (Golden brown algae):
Mainly unicellular or colonial, filamentous forms are unusual. Motile cells contain two equal or unequal flage present on anterior end. Longer one contains stiff hairs and shorter is smooth. Cell wall is composed of pectin and silica or scales of carbonate. Chloroplasts are intensely lobed. Principal pigments are chlorophyll a, c, and carotenoids similar to B-carotene, fucoxanthin diatoxantin and neofucoxanthin. Storage products are mostly oil droplets, and true starch is not present but glucan granules or leucosin are present.
Sexual reproduction is unusual. Many common features are formation of resting cysts, resting spore (statspores), with silica walls. Cysts are formed as result of asexual or sexual reproduction. Golden-brown algae are spread in marine and fresh water habitats, and in fast flowing mountain streams. Marine coccolithophorides are liable for structure of chalk beds on bottom of sea. For e.g.: Chromulina, Symira, Ochromonas, Dinobryon and Mallomoanas.
Division EUGLENOPHYTA (Euglenoids):
Many euglenoids are simple unicellular motile flagellates. They do not have firm cell wall, and have features lime protozoans. They contain the contractile vacule. Cell surface is pellicle (thin membrane) and contains helical; knob like projections. Cell shape alters continually (eulenoid-movements).
Chloroplasts illustrate variety of shapes like discoid, ribbon like or stellate. Cells are biflagellate but only one flagellum comes out anteriorly. Photosynthetic pigments found in plastids comprise chlorophyll a, b and carotenoids including B-carotene. Few euglenoids are also colorless. The form of starch-paramylon is present as distinct granules. Oil droplets and polyphosophate granulets are common in cells. Cells split by bianary fission. Several species make cysts under adverse states. Sexual reproduction is absent. Englenoids happen in fresh water and brackish water and very usually in polluted ponds and temporary rain water pools. For e.g.: Euglena, Trachelomonas and Phacus.
Division DINOPHYTA (Dinoflagelles):
Cell wall comprises of cellulose plates that are inside plasma membrane. The number of plates or body scales may be present on cell wall. Cell structure is complex. Majority of forms are unicellular and motile. Several dinoflagellates like Noctiluca, are luminescent. They glow in dark when they are disturbed. Most of the algae contain chlorophyll, a and c and distinctive arotenoid specific to dinoglagellates.
Reserve foods are mostly in form of starch and oil. Asexual method of reproduction is by cell division. Parent cell separates into the number of aplanospores or zoospores or non-motile cells. Sexual reproduction has been lately reported, gametes are smaller than vegetative cells and fusion is isogamous. Formation of cysts with or without pagemtic fusion is also created.
Dinoflagellates are mainly discovered as marine phytoplankton, at times as retide' blooms. Several happen as symbionts in marine animals such as corals (zooxanthellae).
For e.g.: Noctiluca, Gonyaulax, Peridinium and Ceratium.
Division CRYPHOPHYTA (Crytomonads):
Unicellular motile organisms, when alive they are brown in color. Many genera are animal like in morphology and method of nutrition; few are colorless and saprophytic in nature. Cells are with no cell wall ovoid and dorsiventrally flattened. Two flagella are apical and uneven in length. Chloroplasts may be single or numerous in a cell. In some crytomonads there are two, large parietal chloroplasts, or several disc like ones. Pigments comprise chlorophyll a, c, phycocyanin, phycoerythrin and diverse carotenoids.
Reserve photosynthate is starch.
Reproduction is by longitudinal division of cell. Palmelloid forms might generate zoospores. Sexual reproduction hasn't been reported so far. For e.g.: Crytomonas, Chroomonas.
Division BACILIATIOPHYTA (diatoms):
Mainly unicellular forms, few are colonial and filamentous in structure. Cell wall is silicified, comprising of 2 perforated overlapping plates. It is extremely ornamented on surface. Chromatophores are brownish in color because of large amounts of carotenoids. Photosynthetic pigments are chlorophyll a and c, diatoxanthin, fucoxanthin, diatinoxanthin and diatoxanthin.
General storage product is oil and chrysolaminarin. Reproduction happens by vegetative and sexual methods. Diatom cells unlike other algae are diploid in nature. Sexual fusion is homothallic, inside individuals of same clone. Two amoeboid gametes fuse to make zygote that develops into auxospore. Fusion may be oogamous, isogamous, or anisogamous type.
Diatoms are extensively dispersed in fresh water and sea as planktons, on mud surface, moist rocks and sand. They may even be epizoid, epiphytic or endozoid. Vast deposits of fossil diatom shells known as diatomaceous earth are mined and utilized in different industries. For e.g.: Navicula, Coscinodiscus, Diatoma and Fragilaria. At end we would like to indicate that categorization of algae is uncertain and can be enhanced by employing new and enhanced techniques such as DNA fingerprinting etc. that can explain genetic relatedness of organisms.
Orderly Position of Some Genera:
Family - Chroococcaceae,
Order - Chroococcales,
Division - Cyanophyta
Family - Nostoceceae,
Order - Nostocales
Family - Chlamydomonadaceae
Order - Volvocales
Division - Chlorophyta.
Division - Chlorophyta
Family - Ulotrichaceae,
Order - Ulotrichales,
Family - Ulvaceae
Family - Oedogoniaceae,
Order - Oedogoniales,
Family - Coleochaetaceae,
Order - Chaetophorales
Family - Chaetophoraceae,
Family - Ectocarpaceae,
Order - Ectocarpales,
Division - Phaeophyta.
Family - Fuscaceae,
Order - Fucales,
Family - Laminariaceae,
Order - Laginariales,
Family - Rhodomelaceae,
Order - Ceramiales,
Division - Rhodophyta.
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