@Ebirah766 the tanks have small labels, meaning I could only see a few but according to the stocklist at the start of the year, the following species are held:
I just got to say thank you for providing a glimpse into this cool area. Also I would like to know if there is any plans on restocking P. hyalina, or are they just going to remove them entirely?
No problem, ZSL has some amazing projects. It appears that Londons population of P. hyalina have been reintroduced as you can see individuals being released on this page: Partula snail conservation | ZSL
I would imagine that this is why there has been such a decrease as last year they are listed as holding 118 individuals. Also looking at a video from ZSL Whipsnade, it seems to show the individual being introduced: