Nomen novum

In biological nomenclature, a nomen novum (Latin for "new name"), new replacement name (or replacement name, new substitute name, substitute name) is a technical term. It indicates a scientific name that is created specifically to replace another scientific name, but only when this other name can not be used for technical, nomenclatural reasons (for example because it is a homonym: it is spelled the same as an existing, older name); it does not apply when a name is changed for taxonomic reasons (representing a change in scientific insight). It is frequently abbreviated, e.g. nomen nov., nom. nov., or more explicitly by the rank specified, e.g. superordo nov.

In zoology establishing a new replacement name is a nomenclatural act and it must be expressly proposed to substitute a previously established and available name.

Often, the older name cannot be used because another animal was described earlier with exactly the same name. For example, Lindholm discovered in 1913 that a generic name Jelskia established by Bourguignat in 1877 for a European freshwater snail could not be used because another author Taczanowski had proposed the same name in 1871 for a spider. So Lindholm proposed a new replacement name Borysthenia. This is an objective synonym of Jelskia Bourguignat, 1877, because he has the same type species, and is used today as Borysthenia.

Also for names of species new replacement names are often necessary. New replacement names have been proposed since more than 100 years ago. In 1859 Bourguignat saw that the name Bulimus cinereus Mortillet, 1851 for an Italian snail could not be used because Reeve had proposed exactly the same name in 1848 for a completely different Bolivian snail. Since it was understood even then that the older name has always priority, Bourguignat proposed a new replacement name Bulimus psarolenus, and also added a note why this was necessary. The Italian snail is known until today under the name Solatopupa psarolena (Bourguignat, 1859).

A new replacement name must obey certain rules, not all of these are well known.

Not every author who proposes a name for a species that already has another name, establishes a new replacement name. An author who writes "The name of the insect species with the green wings shall be named X, this is the one that the other author has named Y", does not establish a new replacement name (but a regular new name).

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