Diatoms? (microscope)

[CloudReefer]

Hi all, have a bunch of icky crud on my sand and finally got a microscope. I thought I had dinos but now not so sure.

Are these diatoms? Both at 400x and under a coverslip. These were from a clump on my sandbed. The first is the edge of the clump and the second are some other organisms I saw off to the side that I thought offered a better image.

 

[taricha]

Looks like there's a lot of diatoms in that mat, but I think I also see cyano in there holding it together as well.

 

[CloudReefer]

Weird that I've got so many diatoms. I need to get a Si tester now. blergh.

This mat recedes a fair bit at night, and I found these guys too. Amphidinium of some sort? I got these samples as the mat was starting to recede so I wonder if during the day when it's thicker it's full of dinos, and in the evening they go into the sand and leave behind just the diatoms.

Also found some round pod looking things and worms moving around eating stuff. Wonder what those are too.