Cyphoderia sp.

 

 

Cyphoderia species

 

I found these specimens in a sample from the Naardermeer, in an eutrophic ditch in floating debris. From these observations it's impossible to make any correct identification.

 

Around the aperture a veil is visible.
Dividing cells which show that the daughter shell can be quite different from the mother shell. I've also observed that a daughter shell had a 'trochus' and the mother was smooth.
Shell structure
Shell structure