Zoological Nomenclature: Distinguishing Available and Unavailable Names
In the complex world of biological classification, precision is everything. When scientists identify a new animal, they must follow strict rules to ensure that every organism has a unique and universally recognized identity. This system is governed by the International Code of Zoological Nomenclature (ICZN). Central to this system is the distinction between an available name and an unavailable name—a distinction that determines whether a name can officially exist in the scientific record.
An available name is a scientific name for an animal taxon (a group of organisms) that has been published after 1757 and adheres to all mandatory provisions of the ICZN. If a name fails to meet these specific requirements, it is deemed unavailable and cannot be used as a valid name for a taxon.
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Key Facts
- Availability: A name must follow ICZN rules and be published after 1757 to be considered available.
- Typification: Every available name must refer to a type (a physical anchor like a holotype) to ensure scientific accuracy.
- Validity: An available name is not always a valid name; it may be rejected if it is a duplicate (homonym) or a synonym.
- Botanical Difference: Botany uses different terminology, such as "validly published name" instead of "available name."
- Nomen Nudum: This refers to a name published without an accompanying description, making it unavailable.
Requirements for an Available Name
For a name to achieve availability, it must satisfy several rigorous criteria beyond mere publication. These rules ensure that the name is descriptive, unique, and stable. Key requirements include:
- The name must include a description or definition of the taxon.
- It must use only the Latin alphabet.
- It must be formulated within the binomial nomenclature framework (a two-part naming system).
- It must be a newly proposed name, not a mere redescription of a previously available taxon.
- It must be used as a valid name rather than a synonym.
- It cannot be used for a hybrid or a hypothetical taxon.
- It cannot be used for a taxon below the rank of subspecies.
In rare historical instances, the rules are slightly more flexible. For example, an illustration published before 1930 may render a name available even if a formal description was missing, provided it meets specific criteria under Article 12.2.7 of the Code.
The Importance of Typification
All available names must be anchored to a type. This provides a concrete empirical reference point for the name. The nature of the type depends on the taxonomic rank:
- Species level: Usually a single specimen, such as a holotype, lectotype, or neotype.
- Generic level: A single species serves as the type.
- Family level: A single genus serves as the type.
Understanding Unavailable Names
An unavailable name is one that fails to meet the requirements set forth in Articles 10 through 20 of the Code. There are several categories of unavailable names:
- Unpublished names: Names that have not been formally released in scientific literature.
- Nomina nuda: Also known as a nomen nudum, these are names proposed without an accompanying description.
- Infrasubspecific names: Names proposed for ranks below the level of subspecies.
It is a common misconception that all unavailable names are nomina nuda. For instance, the dinosaur name Ubirajara jubatus was determined to be an unavailable name through detailed nomenclatural analysis, despite not being a simple nomen nudum.
Available vs. Valid Names
It is vital to distinguish between an available name and a valid name. While every valid name must be available, not every available name is valid. An available name might be rejected from use if it is a homonym (the same name used for two different animals) or if it is placed into synonymy (when it is determined that the name refers to a taxon that already has a different, established name).
| Term | Status | Definition |
|---|---|---|
| Available Name | Meets ICZN rules | A name that fulfills all publication and formal requirements. |
| Unavailable Name | Fails ICZN rules | A name that lacks description, is unpublished, or fails other criteria. |
| Valid Name | Correctly applied | An available name that is not a synonym or a homonym. |
| Nomen Nudum | Unavailable | A name published without a formal description. |
Frequently Asked Questions
Is an available name always the correct name for an animal?
No. An available name is simply one that follows the rules of publication. It only becomes the "valid name" if it is not a synonym or a homonym of another name.
What is the difference between zoological and botanical nomenclature?
The terms differ. In zoology, we speak of "available names," whereas in botany (governed by the International Code of Nomenclature for algae, fungi, and plants), the equivalent term is "validly published name."
Can a name be available if it only has an illustration?
Yes, but only in rare historical cases. Under Article 12.2.7, an illustration published prior to 1930 may allow a name to be available even without a formal description.
What happens to an infrasubspecific name?
Names proposed for ranks below the level of subspecies are considered unavailable under the current rules of the ICZN.
What is a type specimen?
A type specimen is a physical object (like a single specimen for a species) that serves as the permanent scientific anchor for a name, ensuring researchers know exactly which organism the name refers to.