Xanthophyceae Classification Essay

Classification of Algea

F.E. Fritsch (1944-45) classified algae into 11 classes in his book 'Structure and Reproduction of Algae' based on the following characteristics.

1. Pigmentation 2. Reserve food 3. Flagellar arrangement 4. Thallus organization 5. Reproduction.

The 11 classes of algae are:

1. Chlorophyceae  

2. Xanthophyceae  

3. Chrysophyceae

4. Bacillariophyceae        

5. Cryptophyceae    

6. Dinophyceae  

7. Chlromonodineae 

8. Euglenophyceae 

9. Phaeophyceae 

10. Rhodophyceae 

11. Myxophyceae

Thallus organization

The thalli of algae exhibit a great range of variation in structure and organization. It ranges from microscopic unicellular forms to giant seaweeds like Macrocystis which measures up to 100 meters long. Some of them form colonies, or filaments. The unicellular form may be motile as in Chlamydomonas or non-motile as in Chlorella. Most algae have filamentous thallus. eg. Spirogyra. The filaments may be branched.

Cell Structure & Pigmentation

With the exception of blue green algae which are treated as Cyanobacteria, all algae have eukaryotic cell organization. The cell wall is made up of cellulose and pectin. There is a well defined nucleus and membrane bound organelles are found.

Three types of Photosynthetic pigments are seen in algae.          

They are 1. Chlorphylls 2. Carotenoids 3. Biliproteins.

Nutrition and reserve food materials in Algae

Algae are autotrophic in their mode of nutrition. The carbohydrate reserves of algae are various forms of starch in different classes of Algae. For example, in Chlorophyceae, the reserve food is starch and in Rhodophyceae it is Floridean starch, in Phaeophyceae it is laminarian starch while in Euglenophyceae it is paramylon. Members of Phaeophyceae storemannitol in addition to carbohydrate. Members of Xanthophyceae and Bacillariophyceae store fats, oils and lipids. The nature of reserve food material is also another important criterion used in classification.

Arranagement of Flagella

Flagella or cilia( sing.flagellum / cilium) are organs of locomotion that occur in a majority of algal classes. There are two types of flagella namely whiplash (Acronematic) and tinsel (pantonematic).

Reproduction

Three common methods of reproduction found in Algae are 1. Vegetative 2. Asexual and 3. Sexual

A Microbial Biorealm page on the phylum Xanthophyceae

Classification

Higher order taxa:

Eukaryota; stramenopiles

Genera

Vaucheria, Tribonema, Botrydium

Description and Significance

Commonly called the yellow-green algae. There are about 600 species of Xanthophyceae, all but three (Botrydium, Tribonema and Vaucheria) of the species are very rare. Before 1899 there were so few species known that they were categorized with the Chlorophyta (green algae). They are often confused with green algae because it is pigmented by chlorophyll and lacks the fucoxanthin that is present in other Chyrsophyta. In fact, Xanthophyceae are "secondary endosymbionts" -- they evolved from protists that engulfed algae and assimilated their chloroplasts. The two main varieties appear as large green vesicles up to several mm in diameter.

Genome Structure

There has not been a genome project on Xanthophyceae yet, however there have been some experiments studying how the organism can morph to adapt to frigid waters. There is also evidence from DNA sequence comparison that Xanthophyceae is genetically related to Raphidophyceae (click here for abstract on research.)

Cell Structure and Metabolism

Xanthophyceae are a photosynthetic group of yellow-green algae. Their photosynthate is stored as oils and the storage polymer chrysolaminarin. Most Xanthophyta are coccoid or filamentous, but some are siphonous, meaning that they are composed of multiple tubular cells with several nuclei. What makes up the cell wall is unknown but inside some there are two silica valves similar to those in diatoms. For the species that are filamentous the interlocking halves are in the shape of a H.

While not much is known about the life cycle of xathnophyta generally their reproduction is asexual, in which the cell divides bilaterally and creates and produces an endogenous cyst. Reproduction has only been observed in two xanothophtyes: in Vaucheria, it was found to be oogamous, and Botrydium reproduces by means of bimastigote zoospores or aplanospores.

Ecology

Xanthophyta are generally found in freshwater, wet soil and tree trunks, but there are several marine species. Most of the species occur singly and are found around other algae, making it difficult to find the same species twice. They do very well at low pH in habitats that are rich in iron. It was also found that Xanthophyceae loses its cytoplasmic streaming ability and organization of other vegetative filaments, when it is in an aluminum-rich environment. Many of them are found in late winter among floating mats in still water.

The species Vaucheria longicaulis has a unique characteristic in that it will send a larvae of Alderua modesta into spontaneous metamorphorosis when the larvae comes in contact with it. The adults can create two kinds of larvae, planktotrophic or lecithotrophic. Lecithotrophic clutches contain a mix of larvae, some which settle spontaneously, and others that need to be exposed to Vaucheria longicaulis.There were other experiments done to test and see if other algae would have the same effect and out of the 17 none did except for Vaucheria longicaulis.

[[Image:Botrydium_bubbles.jpgBotrydium granulatum. Photo by: Bioimages]]

References. Updated June 22, 2005

Alessa, L., Oliveria, L. Aluminum toxicity studies in Vaucheria longicaulis var. macounii (Xanthophyta, Tribophyceae). I. Effects on cytoplasmic organization. Environmental and Experimental Botany. v. 45. 3 (2001) 205-222.

American Journal of Botany. D. Potter, G.W. Saunders and R.A. Anderson.Phylogenetic relationships of the Raphidophyceae and Xanthophyceae as inferres from nucleotide sequences of the 18S ribosomal RNA gene.

BIODIDAC. Ivy Linginstone.Protista- Chrysophyta. Vaucheria- Sexual and asexual reproduction in the yellow green alga Vaucheria.

Bioimages- Virtual Field-Guide (UK). Botrydium granulatum (a yellow green algae). .Sept. 28, 2002.

Department of Environment and Conservation.Botanic Garden Trust. Entwisle.

Hibberd, David J. Phylum Xanthophyta. Handbook of Protoctista. (pg 686-697). Jones and Bartlett Publishers, Boston. 1990.

Krug, Patrick J. Bet-Hedging Dispersal Stategy of a Specialist Marine Herbivore: a Settlement Dimorphism Among Sibling Larvae of Alderia modesta. Marine Ecology Progress Series. April 4, 2001.

Patterson, Mark. Aquatic Phototrophs: Algae, Cyanobacteria and Prochlorophytes.

B. R. Speer. University of California. Museum of Paleontology.Introduction to Xanthophyta.

University of Kentucky College of Agriculture. Class Notes.Lecture 14- Algae.

University of Maryland. Heterokontophyta III - Xanthophyceae & Eustigmatopyceae.

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