This is a marine flagellate, and I admit it is not really looking like a happy cell...

Focussing at the surface gives a hint of what it might be:

It is stained with a fluorescent brightener, one that makes your wash whiter then white (or so the slogan goes) 8)
This way the thecal plates of this so-called armored flagellate stands out, otherwise I probably wouldn't have spotted it in the sample:

Sample from the Wadden Sea, stack of 11 images with 20x/0.7. Width of the cell is 20 um.
Identification to species is tricky, but the shape of the pore on top is a give-away for Scrippsiella.
Here's one such pore, top view:

With this pore it can attach itself to a substrate, as the start of encystment.
Best wishes, René
