It seems to be Staurastrum. but not sure because of low resolution.

Staurastrum-top

bottom too blurry to determine--maybe a piece of Chara or Nitella

I had come across with this type staurastrum while analysing some epiphytic samples from Mangalavanm.

This is epiphytic alga from mangalavanam, kochi

Thank you very much friends. I found some images similar to mine, could be Actinastrum (b).

http://protist.i.hosei.ac.jp/PDB/Images/chlorophyta/actinastrum/sp_02.html

The resolution isnt good enough for a good determination but

a) Staurastrum

b) i dont know but it is not Actinastrum

regards 

Agree with Maria:

a) Staurastrum

b) Not Actinastrum but maybe chains of Tabellaria (diatom)

Dear Wetzel sir,

Thank you very much, I found exactly similar figures (Eunotia) in your paper.

A) Staurastrum

B) Tabellaria

I agree with Paulo...Organism A is Staurastrum while organism B is Tabellaria. 

In Tabellaria, the cell arrangement was regular (mostly asteroid) but here it is irregular in all groups.

As said by Carlos E. Wetzel it looks like Eunotia asterionelloides/ Fragilaria zasuminensis/ Eunotia zasuminensis.

1) Staurastrum

2) Eunotia