Way back in my second year of university I got to play with a scanning electron microscope for one of my assignments. I was given a sample of lagoon sand from the Solomon Islands and had to prepare a specimen stub with a few of the interesting-looking tiny organic shelly particles.
The top image (A) is a “star sand” foraminiferan (Family Calcarinidae, Genus Baculogypsina).
The lower one (B) is a gastropod shell. That’s as far as I could identify it. :c