Hello Ernst !
It's coming from my usual Mediterranean plankton soup!
I found (probably) the same parasite (Oodinium poucheti) on Oikopleura dioica.
Have a nice day!
Hallo Franz,
do you know Hoppenrath et.al.,Marine Phytoplankton (North Sea)? Oodinium pouchetii is shown there on page 205. Oikopleura is also mentioned there.