Very nice set of photos. I have never seen Centropyxis but live in hope. I understand that the test is built from minute grains of sand (nicely evidenced in your pic1) - so I assume the colour and granular texture must vary from location to location?
Those spiney testate amoeba are so neat! Very 3D though, and a photographic challance. You did a great job (especially in the first shot) of showing those "spines" clearly.