[bugbotherer]

Lymnaea stagnalis is a pulmonate snail and hermaphroditic, so the book needs some molluscs awareness and the centre is on the right lines. In my experience it's generally those snails with an operculum (hinged lid that covers the shell opening when the snail retracts) that have both sexes. I've kept L.stagnalis in culture and the oldest was 3 years old when she/he slipped away