The following points highlight the eleven main classes of algae. The classes are: 1. Chlorophyceae 2. Xanthophyceae 3. Chrysophyceae 4. Bacillariophyceae 5. Cryptophyceae 6. Dinophyceae 7. Chloromonadineae 8. Euglenineae 9. Phaeophyceae 10. Rhodophyceae 11. Cyanophyceae or Myxophyceae.
Class # 1. Chlorophyceae (Green Algae):
Unicellular, colonial or multicellular green plants, generally with simple structure, principal pigments are chlorophyll a and b, carotenes and xanthophyll’s as in higher plants, contained in plastids.
Food storage products are mostly starch and sometimes fat frequently aggregates around the pyrenoids. Reproduction is by asexual and sexual means. Zoospores biflagellate or quadriflagellate flagella anterior isokontae, whiplash type, cell wall of cellulose and pectin, fresh water or marine.
Class # 2. Xanthophyceae (Yellow Green Algae):
Mostly unicellular, most advanced forms have a simple filamentous habit, principal pigments are chlorophyll a and e, β-carotene and xanthophyll’s, reserve food mostly fat, sexual reproduction rare and isogamous, cell wall frequently consists of two overlapping halves, constituents are pectin and silica, sometimes cellulose, the motile cells with two unequal flagella at the anterior, one tinsel and the other whiplash type, most abundant in fresh water, a few are marine.
Class # 3. Chrysophyceae (Golden Algae):
Mostly unicellular, colonial and filamentous forms rare, principal pigments are chlorophyll a, P-carotene and xanthophyll’s, storage product fat, sexual reproduction rare, specialized resting cells known as cysts produced endogenously, flagellated forms have either one flagellum tinsel type or when two one tinsel and one whiplash type, cell wall consists of pectin and silica, fresh water and marine.
Class # 4. Bacillariophyceae (Diatoms):
All unicellular or colonial, principal pigments are chlorophyll a and c, β-carotene and xanthophyll’s, storage product in the form of fat, sexual reproduction is of widespread occurrence, cell wall of pectin and silica, silicified cell wall, precise nature of motile bodies not known, fresh water, marine and terrestrial.
Class # 5. Cryptophyceae:
Unicellular flagellated forms, scantly represented group, principal pigment nature not definitely known, except the phycobilins, reserve food a form of starch, cell wall of cellulose, two unequal flagella, sexual reproduction rare and isogamous, fresh water and marine.
Class # 6. Dinophyceae:
Majority with motile unicelled structure, principal pigments are chlorophyll a and c, β-carotene and xanthophyll’s, reserve food starch or fat, sexual reproduction rare and isogamous, mostly marine a few are fresh water, many colourless forms.
Class # 7. Chloromonadineae:
Unicellular, chromatophore bright green with excess of xanthophyll’s, reserve food is fat, motile cells are biflagellate, only fresh water.
Class # 8. Euglenineae:
Simple unicellular or colonial motile organisms, pigments chlorophyll a and b, (β-carotenes, xanthophyll, reserve food a polysaccharide paramylon, related to starch, and fats, sexual reproduction not proved definitely, no cell wall, motility by flagella, usually one or sometimes more, tinsel type.
Class # 9. Phaeophyceae (Brown Algae):
Structurally the most complex algae, simple filaments to massive plant bodies. Pigments include chlorophyll a and c, β-carotene and xanthophyll’s, stored food in the form of laminarin (polysaccharide) and mannitol form of alcohol, cell wall constitution algin, fucoidin and cellulose, sexual reproduction ranges from isogamy to oogamy, motile cells only in swarmer’s, two unequal flagella attached laterally, one tinsel and the other whiplash type, most of the species are marine.
Class # 10. Rhodophyceae (Red Algae):
Most forms multicellular (complex), pigment contents are chlorophyll a and d, α- and β-carotene and xanthophyll’s, phycobilins—r-phycoerythrin and r-phycocyanin, reserve food in the form of floridean starch, cell wall constitution polygalactose sulphate esters and cellulose, motile cells at any stage of the life history are unknown, sexual reproduction advanced oogamous type, mostly marine, a few are fresh water.
Class # 11. Cyanophyceae or Myxophyceae (Blue-Green Algae):
Simple unicellular, colonial or multicellular bodies lacking nuclear, mitochondrial and chloroplast double membranes, pigments not in organized bodies as in other cases, principal pigments are chlorophyll-a, β-carotene, xanthophyll’s and phycobilins, c-phycoerythrin and c-phycocyanin, reserve food in the form of cyanophycean or myxophycean starch, cell wall composed of pectin or cellulose, most forms are embedded in mucilaginous or gelatinous sheaths, no motile cell has been observed at any stage, reproduction of the bacterial type, ‘false’ branching and special types of cells called ‘heterocyst’ are characteristic features in many, most diverse in distribution, from pole to pole, almost everywhere, ubiquitous.