Facts
Gastropods in general are the most common group of mollusks and make up about eighty percent of the living mollusks. They can be terrestrial, marine, freshwater, etc. They live in just about every type of habitat on Earth. Not only do Gastropods have diverse habitats, they also eat diverse kinds of foods. Some are herbivorous, while some others are carnivorous. Herbivorous Gastropods eat things such as vegetation while carnivorous ones eat flesh.
Most Gastropods have separate sexes, with the exclusion of some including Heterobranchia. Although they can be hermaphroditic, Gastropods do not often self-fertilize, but rather cross fertilize.
Gastropods are characterized by having a single shell, (except the Nudibranchs). Some Gastropods also undergo torsion, which turns the body 180 degrees, and therefore places the anus directly next to or above the head. This is useful, in reducing the entry to the shell to one hole, but can cause problems with fouling, which is when the excrements of the Gastropod wash over the gills. Most Gastropods have a well-developed head, with a pair of tentacles that usually have eyes of some sort at the end.
Http://www.ucmp.berkely.edu/taxa/inverts/mollusca/gastropoda.php
Land snails tend to group together based on six main characteristics, types of habitats, make up of soil in habitat, geography, amount of moisture, and "presence of anthropogenic disturbance." (Nekola, J., 2003)