BIO 203


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.