Could you provide some informations like dimensions, is it siliceous or other...

It is in agar plate and focused at 40x

This is at 100x

It could be Botryococcus sp. Does it sink at the bottom or it floats on the surface?

If it floats on the surface or around the edges, it could be botryococcus. Try to put it on the slide and press it with coverslip to check if some oil droplets oozes out?

I agree with Simrat.

Go for sequencing.

it is very clear it is not Botryococcus and you can easly make identification at level of species as regrding to genous I'm sure it is a Cosmarium which is a microalgae of Desmides which always appear as two semi cells joint each other by a small part where you can find the nucleus so it appears always as one cell in the late binary fission stage

check this similar Cosmarium species

Thanks everyone for all your valuable suggessions