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Inzoological nomenclature, atype species (species typica) is thespecies whose name is considered to be permanently taxonomically associated with the name of agenus orsubgenus. In other words, it is the species that contains the biologicaltypespecimen or specimens of the genus or subgenus.[1] A similar concept is used for groups ranked above the genus and called atype genus.[2]
Inbotanical nomenclature, these terms have no formal standing under thecode of nomenclature, but are sometimes borrowed from zoological nomenclature. In botany, the type of a genus name is a specimen (or, rarely, an illustration) which is also the type of a species name. The species name with that type can also be referred to as the type of the genus name. Names of genus and family ranks, the various subdivisions of those ranks, and some higher-rank names based on genus names, have such types.[3]
Inbacteriology, a type species is assigned for each genus.[4] Whether or not currently recognized asvalid, every named genus or subgenus in zoology is theoretically associated with a type species. In practice, however, there is a backlog of untypified names defined in older publications when it was not required to specify a type.
A type species is both a concept and a practical system that is used in theclassification and nomenclature (naming) of animals. The "type species" represents the reference species and thus "definition" for a particular genus name. Whenever a taxon containing multiple species must be divided into more than one genus, the type species automatically assigns the name of the original taxon to one of the resulting new taxa, the one that includes the type species.
The term "type species" is regulated inzoological nomenclature by article 42.3 of theInternational Code of Zoological Nomenclature, which defines a type species as thename-bearing type of the name of a genus or subgenus (a "genus-group name"). In the Glossary, type species is defined as
The nominal species that is the name-bearing type of a nominal genus or subgenus.[5]
The type species permanently attaches a formal name (the generic name) to agenus by providing just onespecies within that genus to which the genus name is permanently linked (i.e. the genus must include that species if it is to bear the name). The species name in turn is fixed, in theory, to a type specimen.
For example, the type species for theland snail genusMonacha isHelix cartusiana, the name under which the species was first described, known asMonacha cartusiana when placed in the genusMonacha. That genus is currently placed within the familyHygromiidae. The type genus for that family is the genusHygromia.
The concept of the type species in zoology was introduced byPierre André Latreille.[6]
TheInternational Code of Zoological Nomenclature states that the original name (binomen) of the type species should always be cited. It gives an example in Article 67.1.Astacus marinusFabricius, 1775 was later designated as the type species of the genusHomarus, thus giving it the nameHomarus marinus(Fabricius, 1775). However, the type species ofHomarus should always be cited using its original name, i.e.Astacus marinusFabricius, 1775, even though that is ajunior synonym ofCancer gammarusLinnaeus, 1758.[1]
Although theInternational Code of Nomenclature for algae, fungi, and plants does not contain the same explicit statement, examples make it clear that the original name is used, so that the "type species" of a genus name need not have a name within that genus. Thus in Article 10, Ex. 3, the type of the genus nameElodes is quoted as the type of the species nameHypericum aegypticum, not as the type of the species nameElodes aegyptica.[3] (Elodes is not now considered distinct fromHypericum.)
The name-bearing type of a nominal family-group taxon is a nominal genus called the "type genus"; the family-group name is based upon that of the type genus
