El juego de la vida

The Protista (or Protistes ) form a group of classification of the living beings.

The first definition of a reign of the Protista was proposed by Ernst Haeckel in 1866 by gathering all that with its direction and at the time corresponded neither to the plants (or Plantae ), nor with the animals.

The concept of Protista then perduré during more than one century, but the delimitation of this " règne" often and strongly varied according to the authors.

Today, the Polyphyletic character of the Protista , whatever their definition, was shown, reducing considerably the relevance of such a group in addition without ecological or morphological unit. Thus, phylogenetic classification is unaware of Protistes completely.

Traditional classification

One distinguishes, according to the conventional system of classification in progress, three types of cells, having significant differences on the level of the structure and function.

The eucaryotes, are mono or multicellular living being which includes/understands the following reigns: vegetable , the Eumycète S and animal and protists, composed of unicellular organizations and simple multicellular organizations. Traditional classification supposed them related.

The Procaryote S are the smallest cells, and least elaborate. These simple cells compose the organizations of the field of the bacteria. The Archéobactérie S which then compose the third field of classification.

The term protist (of the Greek Protos = first) indicates the reigns of alive the which gather all the mobile and unicellular living beings. The reign of the protists is generally divided into two parts:

the Protozoon S, with animal affinities
the Protophyte S, with vegetable affinities

Protozoa

The protozoa are unicellular organizations which form a group Paraphylétique, they have a cell Eucaryote (i.e. having a true core, contrary to the bacteria, known as Procaryote S), very differentiated which fills of many functions necessary to the Vie and comprising complex organoids: " vacuoles pulsatiles" , " cils" , " flagelles".

The protozoa are thus different strongly from the constituent cells of fabrics of the Métazoaires . They conquered and adapted to all the mediums of life, and some are parasites which can be really dangerous. Their sexuée or asexual reproduction is very complex.

Four subphyla are distinguished:

the Actinopode S which emit radiant ends pseudopodes. They include/understand:

the Acanthaire S , which are marine protozoa and planctogenic. They are equipped with a celestite test.
the Radiolaires actinopodes , which are marine protozoa with a skeleton Silice ux. Their Sediment ation and them fossilization gives rise to rocks the such Jaspe or the Lydite…
the héliozaires , generally without test, but with silica spicules.

the infusoaires or infusoires are protists of big size (up to 300 μm for the Paramécie). They are provided with a macronucleus and a micronucleus . One distinguishes there:

the holotriches (paramécie)
the spirotriches having an oral ciliature in spiral on the right (Stylonichia)
the péritriches having an oral ciliature in spiral on the left (vorticelle)

the rhizoflagellés which include/understand the rhizopodes and whipped.

the rhizopodes constitute one superclasse protozoa characterized by their aptitude to emit Pseudopode S locomotor and prehensile. One finds in this class the radiolarian Amibe S, rhizopodes and the Foraminifère S .

Foraminifera are in marine and brackish water, and them calcareous test includes/understands several cabins more or less perforated like the globigérines and the nummulites .

the whipped constitute one superclasse protozoa equipped with whip which are bodies thread-like and contractile which ensures the locomotion. One finds in this class the phytoflagellés (vegetable chlorophyllian), and the zooflagellés , animals of which some can be dangerous parasites as the Trypanosome which causes the “Maladie of the sleep”.

the sporozoaires (or Apicomplexes ) are deprived in an adult state of locomotor apparatus. They are parasites of the animal cells equipped with an apical complex and reproducing by sporogony.

Protophytes

Protophytes are unicellular vegetable organizations or with little differentiated cells.

7 subphyla are distinguished:

the Chlorophycées
the Dictyochophycées
the Euglénophycées
the Prymnésiophycées
the Chrysophycées
the Dinophycées
the Xanthophyceae

Modern phylogenetic classification

For modern phylogenetic classification, the reign of the protists is not relevant any more. Certain protists are attached to the Opisthocontes, others with the line of the brown algas (Straménopiles) or with the green line of the algae and terrestrial plants (Chlorophyta). Other “protists” are divided into monophyletic lines which could have row of reign. Lastly, the position of other “protists” to dubious affinities is still under study. On the whole the scientists recognize an about sixty lines today. Moreover, into phylogenetic modern, vegetable and animal become obsolete terms.

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