As in many other cases in reproduction there is a difference between pulmonate and prosobranch freshwatersnails.
Pulmonates are hermaphroditic and prosobranchs have separated sexes.There is one exception however:
the Family Valvatiidae are prosobranch hermaphroditics.
Although hermaphroditics can fertilize themselves this only happens when there are few
snails in a certain area.
Pomacea bridgesi mating
The way the eggs are deposited is very variable,a lot of freshwatersnails lay their eggs
under the watersurface.Rocks,waterplants,the underside of floating waterplants,reeds,wood
and,if kept as pets,the aquariumglass are all places where we can find eggs.
The snails of the genus Pomacea lay their eggs outside the water,the hatched snails will
fall automatically in the water.The color of those eggs can be white,pinkish or reddish.
The eggs of other freshwatersnails are often transparent.
The snails of the Family Viviparidae are ovo-viviparious,this means they give birth
to live young.
In the Family Thiaridae the snails are parthogenetic;females can reproduce without
being fertilized.