Types of Algae With their example

Algae are a group of autotrophic, photosynthetic and non-vascular organisms. They may be unicellular or multicellular in nature. Some algae are microscopic like phytoplankton, while some are large multicellular forms like giant kelp.

Algae contain chlorophyll and prepare their food by photosynthesis. During this process they release oxygen and form organic food materials. For this reason, they were earlier considered as lower plants.

Algae are different from true plants because their body is simple and thalloid. They do not have true root, stem and leaves. They also lack well developed vascular tissue and complex tissue system.

The sex organs of algae are simple. They are not covered by sterile jacket layer. After sexual reproduction, embryo is not formed, which is an important character of algae.

Most true algae are eukaryotic organisms and they are commonly placed under Protista. But blue green algae are not true algae. They are prokaryotic bacteria and called Cyanobacteria.

Algae are found in different habitats. They grow in marine water, fresh water, rivers, lakes, moist soil, snow and also on other organisms. Some algae live in symbiotic association with fungi and corals. Thus algae are a diverse group of simple photosynthetic organisms.

Types of Algae

F.E. Fritsch divides the algae into 11 classes in his book “Structure & reproduction of algae”. He classified algae on the basis of their pigmentation, thallus-structure, reserve food, flagellation & modes of reproduction.

1. Green Algae (Chlorophyta / Chlorophyceae)

• Chlorophyceae are the green algae. They are mostly fresh water forms. Some members are marine and few are also found on wet soil, wet rocks and bark of trees.
• The colour of the members is grass green. It is due to the presence of chlorophyll a and chlorophyll b. Carotenoids and xanthophylls are also present in them.
• The plant body is thalloid and it shows great variation. It may be unicellular, colonial, filamentous or multicellular form.
• Some unicellular members are motile and some are non-motile. Motile members move by the help of flagella.
• The cell wall is made up of cellulose. This is an important character of the members. The reserve food material is starch.
• The starch is generally stored in the chloroplast. In many forms it remains associated with pyrenoids.
• Reproduction takes place by vegetative, asexual and sexual method. Vegetative reproduction is mostly by fragmentation in filamentous forms.
• Asexual reproduction takes place by spores. The common spore is zoospore. These spores are motile and flagellated.
• Sexual reproduction ranges from isogamy to oogamy. In isogamy both gametes are similar. In oogamy female gamete is large and non-motile and male gamete is small and motile.
• Chlamydomonas is unicellular motile green alga. It has two flagella and it swims in water.
• Chlorella is unicellular non-motile green alga. It is nutritive and used as food. It is also used in sewage treatment.
• Volvox is colonial green alga. It forms spherical coenobic colony.
• Spirogyra is filamentous green alga. It forms long unbranched filament and commonly found in fresh water ponds.
• Ulva is multicellular green alga. Its thallus is sheet like. It is marine and commonly called sea lettuce.
• Dunaliella is green alga found in high salt condition. It is used for carotene production.
• Other examples are Scenedesmus, Pediastrum, Cladophora and Acetabularia. Acetabularia was used to know the function of nucleus.

2. Brown Algae (Phaeophyta / Phaeophyceae)

• Phaeophyceae are commonly known as brown algae. The members are mostly marine forms and they are commonly found in sea water.
• The members are brown in colour due to excess amount of fucoxanthin. This pigment masks the green colour of chlorophyll.
• The important pigments are chlorophyll a, chlorophyll c, β-carotene and xanthophylls. Chlorophyll b is absent in them.
• The plant body is thalloid and shows much variation in structure. It may be simple branched filament or large bulky kelp like form.
• The members of Phaeophyceae show the most complex body among algae. In large forms, the thallus may show tissue like differentiation.
• The large brown algae may have holdfast, stipe and blade. Holdfast helps in attachment to rocks, stipe is stem like part and blade is leaf like part.
• In some members, air bladder or pneumatocyst is present. It helps the thallus to float in water.
• Some large kelps also contain conducting tubes. These tubes help in transport of food materials from one part to other part of the thallus.
• The cell wall is made up of cellulose framework. Outside the cellulose wall, alginic acid, alginates and sulphated fucans are present.
• The reserve food material is laminarin and mannitol. Starch is not the reserve food material in brown algae.
• Reproduction takes place by vegetative and sexual methods. Vegetative reproduction is generally by fragmentation of the thallus.
• Sexual reproduction varies from isogamy to oogamy. In isogamy similar gametes are fused and in oogamy large egg fuses with small male gamete.
• The motile reproductive cells are biflagellate. The two flagella are unequal and laterally inserted on the cell.
• Macrocystis is a giant kelp. It may grow up to very large size, about 60 meter long. It is used as a source of alginates, which are used in cosmetics and soaps.
• Laminaria is a kelp rich in iodine. It is used as food and in Japan it is called kombu. It was also used in medicine for goiter.
• Sargassum is a complex brown alga. It forms dense floating masses on the surface of sea water.
• Fucus is commonly found attached to rocks in intertidal region. It has a well developed thallus.
• Ectocarpus is a simple brown alga. It is filamentous and branched in nature.
• Other examples of Phaeophyceae are Dictyota, Ascophyllum, Lessonia and Ecklonia. Some of these are also used as commercial source of algin.

3. Red Algae (Rhodophyta / Rhodophyceae)

• Rhodophyceae are commonly known as red algae. The members are mostly marine forms. Only few members are found in freshwater.
• The members are red or pink in colour. This colour is due to the presence of large amount of phycoerythrin. It masks the green colour of chlorophyll.
• The main pigments are chlorophyll a, chlorophyll d, phycoerythrin, phycocyanin and α-carotene. These pigments help them to carry photosynthesis in deeper water also.
• The plant body is thalloid and shows much variation. It may be simple unbranched filament or highly branched multicellular seaweed like form.
• The members of Rhodophyceae are different from many other algae because flagella are absent. Motile cells are not produced in any stage of life cycle.
• The cell wall is mainly made up of cellulose. The wall also contain mucilaginous polysaccharides like agar and carrageenan.
• In some red algae, calcium carbonate is deposited in the cell wall. These forms become hard and are known as coralline red algae.
• The reserve food material is Floridean starch. It is special carbohydrate and it is not stored inside chloroplast like ordinary starch.
• Reproduction takes place by asexual and sexual methods. Asexual reproduction takes place by spores, commonly by tetraspores.
• Sexual reproduction is specialized and generally oogamous type. The male gametes are called spermatia and they are non-motile.
• As spermatia are non-motile, they are carried by water current to the female sex organ. The female organ is called carpogonium.
• Life cycle of red algae is usually complex. In many members more than one spore producing phases are present.
• Porphyra is an edible red alga. It is cultivated and used as food in Asia. In Japan it is commonly known as nori and used for wrapping sushi.
• Chondrus crispus is commonly called Irish moss. It is an important source of carrageenan, which is used as thickening and stabilizing substance in food, cosmetics and medicines.
• Gelidium and Gracilaria are important red algae. They are chief source of agar-agar, which is used in culture media, capsules and food gels.
• Coralline red algae deposit calcium carbonate in their wall. They help in building and stabilizing coral reefs.
• Other examples of Rhodophyceae are Polysiphonia, Batrachospermum and Porphyridium. Batrachospermum is a freshwater red alga and Porphyridium is unicellular form.

4. Yellow-Green Algae (Tribophyta / Xanthophyceae)

• Xanthophyceae are commonly known as yellow-green algae. The members are mostly freshwater forms and marine forms are very few.
• The members are yellow-green in colour. It is due to presence of excess xanthophylls. So the green colour is not very clear like green algae.
• The important pigments are chlorophyll a, chlorophyll c or sometimes called chlorophyll e, β-carotene and large amount of xanthophylls.
• The thallus shows simple organization. It may be unicellular motile form or filamentous form.
• Some filamentous forms are simple and some are multinucleate. In some members cross walls are absent, so the thallus becomes tubular or siphonous type.
• The cell wall is made up of pectic compounds and cellulose. In many members the wall has two equal overlapping halves.
• These two halves fit at their edges. This is one of the important character of Xanthophyceae.
• Pyrenoids are generally absent. The reserve food material is not starch.
• The reserve food material is oil and chrysolaminarin. These remain stored inside the cell.
• Motile cells have two unequal flagella at the anterior end. One flagellum is tinsel type and other is smooth whiplash type.
• Reproduction takes place mostly by asexual method. Sexual reproduction is rare or absent in most of the members.
• When sexual reproduction is present, it is generally isogamous type. In this type similar gametes are fused.
• Vaucheria is a common example of Xanthophyceae. It is filamentous and siphonous type.
• Botrydium is another important example. It is commonly mentioned under yellow-green algae.
• Other examples are Tribonema and Bumilleriopsis. These are also included under Xanthophyceae.

5. Golden-Brown Algae (Chrysophyta / Chrysophyceae)

• Chrysophyceae are commonly called as golden-brown algae. The members are mostly freshwater forms. Few members are also found in marine water.
• They are generally found in cold freshwater. Some members live as plankton and some forms are attached also.
• The members are photosynthetic in nature. But many members also take bacteria and small organic particles as food, so they show mixed type of nutrition.
• Some forms become colourless due to loss of chloroplast. These members live as heterotrophic forms.
• The colour of the members is yellow, golden brown, brown or orange. This colour is due to excess accessory pigments.
• The important pigments are chlorophyll a, chlorophyll c, phycochrysin, fucoxanthin and other carotenoids.
• The green colour of chlorophyll is masked by phycochrysin and fucoxanthin. So the members appear golden or brownish.
• The thallus is mostly unicellular. Some members form colony. Branched filamentous forms are rare.
• The motile cells usually bear two unequal flagella at the anterior end. One flagellum is long and hairy and another flagellum is short and smooth.
• The hairs present on the long flagellum are called mastigonemes. These help in movement of the cell.
• The cell covering is variable. Some forms are naked and do not have rigid wall.
• Some members have covering made up of pectin. Some have siliceous scales and some have vase like covering.
• The vase like cellulose covering is called lorica. In some colonial forms each cell remains inside its own lorica.
• The reserve food material is not true starch. The reserve food is mainly oil droplets and leucosin.
• Chrysolaminarin is also stored as reserve carbohydrate. It is similar to leucosin.
• Reproduction takes place mostly by asexual method. It occurs by simple cell division or by spore formation.
• Sexual reproduction is rare. When present, it is generally isogamous type.
• Under unfavourable condition, the members form resting cysts. These cysts are called statospores.
• Statospores are heavily silicified. They remain preserved for long time and also form microfossils.
• Dinobryon is a common golden-brown alga. It forms branched tree like colony.
• In Dinobryon, each cell remains inside a vase shaped or funnel shaped lorica. It is also mixotrophic in nutrition.
• Synura forms rounded motile colony. The cells are pear shaped or balloon like and covered by siliceous scales.
• Ochromonas and Chromulina are unicellular flagellated forms. They are common examples of Chrysophyceae.
• Chrysodendron and Phaeothamnion are rare filamentous forms. They show branched filament like body.

6. Diatoms (Bacillariophyta / Bacillariophyceae)

• Bacillariophyceae members are commonly known as diatoms. They are found both in freshwater and marine water. Some members also occur in brackish water, moist soil and other terrestrial damp places.
• The members are yellow or golden brown in colour. This colour is due to presence of diatomin and excess xanthophylls like fucoxanthin.
• The important pigments are chlorophyll a, chlorophyll c, β-carotene, diatomin and xanthophylls. Chlorophyll b is absent.
• The thallus is mostly unicellular. Some members remain attached together and form colony or filament like condition.
• The cell is eukaryotic type. It has nucleus, chromatophores and other cell organelles.
• On the basis of symmetry diatoms are of two types, centric and pennate forms. Centric diatoms show radial symmetry and pennate diatoms show bilateral symmetry.
• The most characteristic feature of diatoms is the cell wall. The cell wall is hard, transparent and siliceous. It is called frustule.
• The frustule is made up of opaline silica with pectic substances. It has many fine markings and ornamentation, so the cell wall appear beautiful.
• The cell wall is made of two overlapping halves. These two halves fit together like a box and lid.
• The upper larger half is called epitheca and lower smaller half is called hypotheca. These parts remain fitted tightly with each other.
• The reserve food materials are oil, volutin, chrysolaminarin and leucosine. Starch is not present as reserve food.
• Reproduction takes place mainly by cell division. During cell division each daughter cell receives one old half of the wall and forms one new half.
• Sexual reproduction is of special type. It takes place by fusion of protoplasts of ordinary vegetative cells.
• The diatom cells are mostly diploid. After repeated division, the size of cells gradually become smaller.
• Under unfavourable condition some members form resting spores or cysts. These are thick walled and heavily silicified.
• The siliceous wall of dead diatoms are not easily destroyed. They settle down at the bottom of sea and form large deposit.
• These deposits are called diatomaceous earth or diatomite. It is used in filters, cleansing powder, polishing material and some industrial works.
• Diatoms are very important phytoplanktons. They prepare food by photosynthesis and form major food source for aquatic animals.
• Some pennate diatoms produce harmful toxins. These may cause harmful effect in water bodies.
• Important examples are Pinnularia, Navicula, Nitzschia, Cyclotella, Thalassiosira and Pseudo-nitzschia.

7. Cryptomonads (Cryptophyta / Cryptophyceae)

• Cryptophyceae members are commonly called as cryptomonads. They are found in freshwater and marine water. The members are mostly small planktonic forms.
• The colour of the members is variable. They may be red, blue-green, olive brown or brown in colour. This colour is due to the presence of different pigments.
• The chief pigments are chlorophyll a, chlorophyll c, phycobilins and carotenoids. α-carotene is also present in them.
• A special carotenoid pigment is present which is called alloxanthin. It is an important pigment of cryptomonads.
• The body is mostly unicellular and motile. Some advanced forms show coccoid or spherical type of body.
• The motile cells possess two flagella. These two flagella are slightly unequal and arise from the anterior region of the cell.
• True rigid cell wall is absent. The cell is covered by a special covering called periplast.
• The periplast is proteinaceous in nature. It is made up of plates or sheets which remain below the cell membrane.
• The cell structure is complex. A furrow or gullet like structure is present in the cell.
• The gullet is lined by special discharging bodies. These bodies are called ejectosomes.
• The members contain a peculiar small nucleus like body. It is called nucleomorph and it represents residual nucleus.
• Chloroplast is also special in these members. It is surrounded by four membranes and it is associated with chloroplast endoplasmic reticulum.
• The reserve food material is starch. It is stored outside the chloroplast and not inside the chloroplast.
• Reproduction takes place mainly by asexual method. It commonly occurs by cell division.
• Sexual reproduction is very rare. When present, it is generally isogamous type.
• Cryptomonas is a common example of cryptomonads. It is unicellular and motile form.
• Chilomonas is also an important example. It is commonly described under Cryptophyceae.
• Chroomonas is another example. Some forms show more advanced coccoid condition.
• Other examples are Teleaulax and Plagioselmis. These are also included under Cryptophyta.

8. Dinoflagellates (Dinophyta / Dinophyceae)

• Dinophyceae are the dinoflagellates. They are mostly unicellular flagellated forms. The members are found in sea water and fresh water.
• Many members occur as plankton. Some are photosynthetic forms and some are animal like in nutrition. Few members show mixed type of nutrition also.
• The colour of the members is brown or dark yellow. Sometimes they appear brownish green also. This colour is because of carotenoid pigments.
• The main pigments are chlorophyll a, chlorophyll c, peridinin, dinoxanthin and diadinoxanthin. The brown pigment masks the green colour of chlorophyll.
• The body is unicellular. Shape of the cell is variable. Some forms are round, some are elongated and some forms bear horn like projection.
• Cell covering may be naked or armoured. In armoured forms the cell is covered by a rigid covering called theca.
• The theca is made up of many cellulose plates. These plates remain fitted with each other and form a hard outer covering.
• The members possess two flagella. The flagella are not equal in position. They lie in two grooves of the cell body.
• One flagellum lies in transverse groove around the cell. Other flagellum lies in longitudinal groove. By the action of these flagella the cell moves in spinning manner.
• This spinning movement is a characteristic feature of dinoflagellates. Due to this movement they are called dinoflagellates.
• The nucleus is special type. It is called dinokaryon. In this nucleus chromosomes remain condensed even in resting condition.
• The chromosomes are attached with the nuclear membrane. This type of nucleus is not like the ordinary eukaryotic nucleus.
• Chloroplast is present in photosynthetic members. The chloroplast is usually surrounded by three membranes.
• Reserve food material is starch and oil. These materials remain stored inside the cell.
• Reproduction takes place by asexual and sexual methods. Asexual reproduction is commonly by simple cell division.
• Sexual reproduction is found in some forms. The life cycle is not simple in many members.
• During unfavourable condition the cell forms resting cyst. These cysts are heavy and settle down at the bottom.
• When favourable condition comes, the cyst germinates again and gives rise to vegetative cell.
• Some members grow very rapidly in nutrient rich water. This rapid growth forms red tide. It is also called harmful algal bloom.
• During red tide, sea water becomes red or brownish in colour. It may cause death of fishes and other aquatic animals.
• Some dinoflagellates produce poisonous substances. Saxitoxin and brevetoxin are important toxins. These toxins may cause paralytic shell fish poisoning in man.
• Some members show bioluminescence. They give blue light in sea water when the water is disturbed by wave or movement.
• Some photosynthetic forms live inside corals. These are called zooxanthellae. They provide food to corals.
• Zooxanthellae are important for coral reef. When these forms are lost from coral, the coral becomes white. This is called coral bleaching.
• Symbiodinium is a symbiotic dinoflagellate. It lives in corals, giant clams and jelly fish.
• Noctiluca is large naked dinoflagellate. It is heterotrophic and shows bioluminescence.
• Ceratium is armoured form. It has horn like projections.
• Alexandrium and Karenia are red tide forming forms. They produce toxic effect and cause shell fish poisoning.
• Akashiwo is unarmoured dinoflagellate. It may form deep coloured red tide in sea water.

9. Chloromonads (Raphidophyta / Chloromonadineae)

• Chloromonadineae members are commonly called as chloromonads. They are mostly freshwater forms and commonly occur in ponds, pools and other fresh water bodies.
• The members are pale green or bright green in colour. This colour is due to presence of excess xanthophylls.
• The chief pigments are chlorophyll a and chlorophyll c. Large discoid chromatophores are present in the cell.
• The body is unicellular and motile. The members are very sensitive in nature and show movement in water.
• Cell wall is absent. So the body is not covered by a rigid wall like many other algae.
• Two flagella are present. These flagella are almost equal in size and help in movement of the cell.
• A special character of this group is presence of many mucocysts. These are mucilage discharging bodies.
• Mucocysts discharge mucilage outside the cell. It helps in protection and sometimes in movement also.
• The reserve food materials are oil, fat and chrysolaminarin. Starch is not the chief reserve food.
• Reproduction takes place only by asexual method. Sexual reproduction is absent in this group.
• Asexual reproduction takes place by longitudinal division. In this process the cell divides lengthwise and forms two daughter cells.
• Trentonia is one example of Chloromonadineae. It is included under freshwater chloromonads.
• Vacuolaria is another common example. It is unicellular and motile form.
• Gonyostomum is also included in this group. Gonyostomum semen is a known example.
• Heterosigma and Chattonella are other examples. Heterosigma akashiwo is commonly mentioned under this group.

10. Euglenoids (Euglenophyta / Euglenophyceae)

• Euglenophyceae members are commonly known as euglenoids. They are mostly freshwater forms. Most of them occur in ponds, pools, ditches and other stagnant water.
• The members are unicellular and flagellated. They show both plant like and animal like characters. So they are considered as connecting form between plants and animals.
• Some members contain chloroplast and prepare their food by photosynthesis. Some members are without chloroplast and take food like animals.
• The photosynthetic members are pure green in colour. The chief pigments are chlorophyll a and chlorophyll b.
• Other pigments are β-carotene, lutein and xanthophylls. These pigments are present in green forms.
• The body is simple and unicellular. The members are motile and move by the help of flagella.
• Cell wall is absent in euglenoids. Instead of cell wall, a flexible covering called pellicle is present.
• The pellicle is proteinaceous in nature. It is made up of many strips and these strips can slide over each other.
• Due to flexible pellicle, the body can change its shape. This movement is called metaboly or euglenoid movement.
• One or two flagella are present at the anterior end. These flagella arise from a canal like structure called gullet.
• A red coloured eyespot is present near the anterior end. It helps in response to light.
• Contractile vacuole is also present. It helps in removal of excess water from the cell.
• The mitochondria have special paddle like cristae. This is also an important character of euglenoids.
• The nucleus is well developed. The chromosomes remain condensed even in interphase condition.
• Reserve food material is paramylon and oil. Paramylon is a special carbohydrate and starch is not the reserve food in them.
• Reproduction takes place by asexual method. It is commonly by longitudinal binary fission.
• Sexual reproduction is absent or very rare. Under unfavourable condition, some members form cysts.
• Euglena is the common and well known example of euglenoids. It is green, motile and shows both plant and animal characters.
• Phacus and Trachelomonas are also common examples. Trachelomonas has a hard outer covering.
• Other examples are Colacium and Eutreptiella. These are also included under Euglenophyceae.
• Trypanosoma is a related protozoan form. It causes African sleeping sickness in man.

11. Blue-Green Algae (Cyanobacteria / Cyanophyta)

• Cyanobacteria are commonly called as blue-green algae. They are prokaryotic organisms and not true algae, but they are studied with algae because they contain chlorophyll a and perform photosynthesis.
• The members are included under Domain Bacteria. They do not possess true nucleus, mitochondria and true chloroplast. The nuclear material is not enclosed by nuclear membrane.
• The members are found in almost all habitats. They occur in freshwater, sea water, hot springs, moist soil, desert soil, wet rocks, bark of trees and other damp places.
• Some members live in symbiotic condition. Nostoc forms association with fungi in lichens and Anabaena occurs in Azolla, which is important in rice field for nitrogen fixation.
• The colour is generally blue-green. Some members may be olive green, brownish or dark green due to variation in pigments.
• The chief pigment is chlorophyll a. Other pigments are c-phycocyanin, c-phycoerythrin, carotenoids and flavicin like pigments.
• The blue colour is mainly due to c-phycocyanin. In some forms red pigment c-phycoerythrin is also present.
• The thallus may be unicellular, colonial or filamentous. Filament may be branched or unbranched.
• The members do not have flagella. Motile reproductive cells are also absent in all stages of life cycle.
• The cell wall is bacterial type and made up of mucopeptide or peptidoglycan. Outside the cell wall mucilaginous sheath is commonly present.
• The photosynthetic lamellae or thylakoids are present in cytoplasm. True chloroplast is absent.
• Reserve food material is cyanophycean starch or glycogen. It is stored in cytoplasm.
• Reproduction takes place only by asexual method. Sexual reproduction is absent.
• Asexual reproduction takes place by binary fission, fragmentation and sometimes by hormogonia. In filamentous forms small fragments break and grow into new filament.
• Some filamentous forms possess heterocyst. It is a thick walled special cell and it helps in fixation of atmospheric nitrogen.
• Some members form resting cells under unfavourable condition. These cells help in perennation.
• Cyanobacteria are important because they produce oxygen during photosynthesis. They also fix atmospheric nitrogen and increase fertility of soil.
• Excess growth of some members causes water bloom. Such bloom may reduce oxygen in water and may produce toxic substances.
• Some cyanobacteria produce toxins like microcystin and saxitoxin. These are harmful for fishes, animals and human beings.
• Microcystis is a common bloom forming form. It forms green scum like layer on the surface of freshwater.
• Spirulina is spiral shaped form. It contains high amount of protein and is used as food supplement.
• Nostoc and Anabaena are filamentous forms. They are important nitrogen fixing cyanobacteria.
• Oscillatoria is an unbranched filamentous form. It shows oscillating movement and moves slowly towards light.
• Cylindrospermopsis is found in tropical and temperate water. Some forms produce toxins which affect liver and kidney.
• Other examples are Gloeocapsa, Chroococcus, Rivularia and Lyngbya.

Other types of Algae

Haptophytes (Prymnesiophyta)

• Prymnesiophyta members are commonly known as haptophytes. They are mostly marine forms. The number of known species is about 300.
• The members are generally golden brown in colour. This colour is due to presence of fucoxanthin and other accessory pigments.
• The chief pigments are chlorophyll a, chlorophyll c and fucoxanthin. These pigments are concerned with photosynthesis.
• The thallus may be unicellular, colonial or filamentous. Most common forms are small planktonic cells.
• The motile unicellular forms generally have two flagella. The two flagella are more or less equal in size.
• Between the two flagella a special thread like organ is present. It is called haptonema.
• Haptonema is the characteristic structure of haptophytes. It is used for attachment and also for catching food particles.
• The chloroplast is surrounded by four membranes. This is an important cellular character of this group.
• The cell surface is often covered by organic scales. These scales remain outside the cell.
• In many members the scales become calcified. These calcified plates are made up of calcium carbonate and are called coccoliths.
• The members with coccoliths are called coccolithophorids. Their body surface looks covered by many small plates.
• The reserve food material is chrysolaminarin. It is a glucose polymer and stored inside the cell.
• Reproduction takes place by both asexual and sexual methods. Both types are common in this group.
• Emiliania huxleyi is a common haptophyte. It has well developed calcified coccoliths and is studied commonly.
• Prymnesium parvum is another important member of Prymnesiophyta. It is a well known form of this group.
• Chrysochromulina is also an example. It has haptonema and uses it in feeding and attachment.

Glaucophyta

• Glaucophyta are a small group of algal forms. The members are mostly unicellular or colonial in nature.
• The colour of the members is generally blue-green. It is due to presence of phycobiliproteins.
• The photosynthetic pigments are present in special bodies called cyanelles. These are primitive blue-green algal like bodies.
• Cyanelles are not true chloroplast like higher algae. They are considered as primitive chloroplast stage.
• The cyanelles retain peptidoglycan like layer. This character shows similarity with cyanobacteria.
• The members may occur as single cell or in colony. The cell organization is simple.
• Motile cells are dorsiventrally symmetrical. It means the upper and lower sides of the cell are different.
• The motile cells have two lateral flagella. These flagella help in movement.
• The reserve food material is starch. It is stored inside the cell as food reserve.
• Glaucocystis is an important example of Glaucophyta. It is non-motile and contains cyanelles.
• Cyanophora is another example. It is motile and shows the characteristic primitive photosynthetic body.

Importance of Algae

• Algae are important aquatic plants. They contain chlorophyll and prepare their own food by photosynthesis. So they act as producer in water bodies.
• Algae produce large amount of oxygen. The oxygen released by marine phytoplanktons is very important for atmosphere.
• Algae take carbon dioxide from water and air during photosynthesis. After death some algal body settle down in sea bottom and carbon may remain stored there.
• In aquatic ecosystem phytoplanktons form the first food. They are eaten by zooplanktons, small fishes and then by large fishes.
• Some dinoflagellates live inside the body of corals. These are called zooxanthellae. They give food to corals and help in coral reef.
• Many sea weeds are used as food. Porphyra is used as nori and Laminaria is used as kombu.
• Spirulina and Chlorella are used as food supplement. They contain protein, vitamins, iron and other minerals.
• Red algae are the source of agar. Agar is obtained from Gelidium and Gracilaria.
• Agar is used in bacteriological culture media. It is also used in food and pharmaceutical work.
• Red algae also give carrageenan. It is obtained from Chondrus crispus and used as thickening and stabilizing substance.
• Brown algae give alginates. It is used in food, cosmetics, soap, toothpaste and other industries.
• Some algal polysaccharides have medicinal value. They show antibacterial, antiviral, antioxidant and antitumor activity.
• Brown algae contain iodine. Laminaria was used in treatment of goiter.
• Some blue green algae fix atmospheric nitrogen. Nostoc and Anabaena are important nitrogen fixing forms.
• Anabaena lives in Azolla. This association is useful in rice field and increases nitrogen of soil.
• Sea weeds are used as manure. They also act as soil conditioner and improve water holding capacity of soil.
• Some algae are used as cattle feed. Some red algae reduce methane production from cattle.
• Algae are used for biofuel production. Oil rich algae give biodiesel and carbohydrate rich algae give bioethanol.
• Chlorella and Scenedesmus are used in sewage treatment. They remove nitrate, phosphate and heavy metals from waste water.
• Algae are also used as indicator of water pollution. Their growth shows the condition of water.
• Diatoms form diatomaceous earth after death. It is made up of siliceous wall of dead diatoms.
• Diatomaceous earth is used in filters, cleansers, polishing powder and mild abrasives.

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