Reproduction
Reproduction in the pulmonate gastropods is one requiring special adaptations, unlike the prosobranch and opisthobranch gastropodia, these terrestrial snails cannot disperse their gametes into the water column.
According to biologist Robert Nordsieck, most terrestrial pulmonate snails are
hermaphroditic, sharing
a common single male and female gonad organ. Not only can
both sexes be present in one organism at one time, but also in
phases, some of which are male and others that are female.
One, or both individuals simultaneously, pass a sperm packet
(spermatophore) to one another thereby fertilizing the other
individual. Self fertilization is uncommon in these
hermaphroditic terrestrial land snails, as eggs and sperm often
develop at different times within the individual.
Once fertilized, the egg develops into its veliger larval
stage. This terrestrial larval stage is found inside of
the egg, as a free swimming larva would have no medium to travel
through. Development in terrestrial snails is direct and
once the veliger matures, a fully formed juvenille snail emerges
from the egg (Nordsieck, R.).
The Helicodiscus parallelus has very limited
information available, therefore this information is a
generalization of it's closely related terrestrial land-snail
relatives. Terrestrial gastropods belonging to the
pulmonata are quite similar in body function and this is a very
good picture of how the Helicodiscidae reproduce.