Help ID nuisance organism on sandbed

[NefTunzReef]

I have attached both sand and microscopic pictures of this brown organism that is starting to coat only my sand bed. Worse with lights on, but not snotty and no air bubble production. My initial thought is that they are some type of dinoflagellate species but they don't match the microscopic pictures of the common types already discussed in Mccarroll's massive Dino thread. Specifically, these motile organisms appear to be HALF TRANSLUCENT under the microscope. Sorry for the image quality as these were taken with my cell phone under microscopy evaluation.

Anyone recognize this particular organism? Thanks in advance.

 

[Ranjib]

I am leaning towards dinoflagellates

 

[NefTunzReef]

Bump.

Sure is suspicious for a certain type of Dino.

Anyone else with a definitive ID?