| Alcadia maxima | |
|---|---|
 | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Mollusca |
| Class: | Gastropoda |
| (unranked): | clade Neritimorpha clade Cycloneritimorpha |
| Superfamily: | Helicinoidea |
| Family: | Helicinidae |
| Genus: | Alcadia |
| Species: | A. maxima |
| Binomial name | |
| Alcadia maxima Sowerby II, 1842 | |
Alcadia maxima is a species of tropical and subtropical land snails with an operculum, terrestrial gastropod mollusks in the family Helicinidae.
In biology, a species ( ) is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. Other ways of defining species include their karyotype, DNA sequence, morphology, behaviour or ecological niche. In addition, paleontologists use the concept of the chronospecies since fossil reproduction cannot be examined. While these definitions may seem adequate, when looked at more closely they represent problematic species concepts. For example, the boundaries between closely related species become unclear with hybridisation, in a species complex of hundreds of similar microspecies, and in a ring species. Also, among organisms that reproduce only asexually, the concept of a reproductive species breaks down, and each clone is potentially a microspecies.
A land snail is any of the numerous species of snail that live on land, as opposed to sea snails and freshwater snails. Land snail is the common name for terrestrial gastropod mollusks that have shells. However, it is not always easy to say which species are terrestrial, because some are more or less amphibious between land and fresh water, and others are relatively amphibious between land and salt water.
The operculum, meaning little lid, is a corneous or calcareous anatomical structure like a trapdoor which exists in many groups of sea snails and freshwater snails, and also in a few groups of land snails; the structure is found in some marine and freshwater gastropods, and in a minority of terrestrial gastropods, including the families Helicinidae, Cyclophoridae, Aciculidae, Maizaniidae, Pomatiidae, etc.
