Presumably formed with phosphate.
Its exact function is unknown.
When the body is divided, each new body "takes" one and then the second "appears".
Typical of Cryptophyta group
In this case we observe in the body of the Chilomonas.
We appreciate the valuable information provided by:
René, Martin Kreutz and Bruce Taylor
In the Forum photomacrography.net forum:
http://www.photomacrography.net/forum/v ... hp?t=26687
Immersion objective, oblique polarized light with retardant.
Link:
https://www.youtube.com/watch?v=nKQmMcdSfLU
Preview:
.

Regards carlos