Name that single celled organism

[TwinReefDad]

Anyone know what this organism is? Found it while looking at some goop on my sandbed under a microscope. There were a couple of them usually by themselves in the sample. This is at 960x magnification.

 

[crazyfishmom]

The cell wall makes me think some form of single cell algae.

 

[The_Paradox]

Looks like some species of Chlorella almost.