Gustavo:

You did not provide scale, but check for Pediastrum simplex Meyen. 

Best

Syed

Dear Dr. Abbas,

Thank you for your answer. Have a nice week.

Kind regards,

Gustavo.

In the slide there are 3 more forms are there one is centre one Pediastrum and side one 4 celled structure is Scenedesmus and  few unicellular bodies may be Chlorella.

These three are the chlorophyceae members and Dictyota is not there, Dictyota is macrophyte belongs to Phaeophyceae

Dear Abbas:

I completely agree with Syed, your picture corresponds to a Pediastrum probably simplex. I am adding a link for seeing this species.

Pediastrum (Chlorophyceae) is a cenobial genus, your species shows 8 cells  arranged in a flat, circular plate, one cell thick. Peripheral cells has one horn-like process. 

http://protist.i.hosei.ac.jp/PDB3/PCD2517/htmls/07.html

Dictyocha speculum (I include a link for comparison) shows a superficial similarity with the Pediastrum. 

Dictyocha (Dictyochophyceae) is an unicelular, uniflagellate, marine genus that bears a silica skeleton in one of the stage of the cycle of life.

http://www.marinespecies.org/photogallery.php?album=1033&pic=39371

Kind regards.

Eugenia

Dear Eugenia,

So helpful like ever! Thank you!

Kind regards,

Gustavo

Dear Gustavo:

You are welcome.

I apologize with you by confunding your name.

Kind regards.

Eugenia

Hi,

The taxon in the center is for sure Pediastrum simplex.

Regards Michael

Hi,

Pediastrum clathratum Lemmerm. / P. simplex Meyen ?var. - in the center, also

Desmodesmus intermedius (Chodat) E.Hegew. var. ... and Chlorella-like green algae

Yes I am also agree with Syed The genus is Pediastrum

Dear Sir, As mentioned by above experts, I also agree with them, the centre one with star-shaped cells, is Pediastrum simplex, the other four celled colony with elongated spines are Scenedesmus, and the one which occupy majority is Chlorella sp. Thank you.

Pediastrum, Scenedesmus and Chlorella are present in this image