Paratype is a technical term used in the scientific naming of species and other taxa of organisms. The exact meaning of the term paratype when it is used in zoology is not the same as the meaning when it is used in botany. In both cases however, this term is used in conjunction with another term, holotype.
The term refers to type material, an actual specimen or specimens of the organism in question on deposit, usually in a museum research collection, in order to help define what the taxon actually represents. Often there is more than one paratype, although there can be only one holotype.
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In zoological nomenclature, a paratype is officially defined as "Each specimen of a type series other than the holotype."[1]
In turn, this definition relies on the definition of a "type series." A type series is the material (specimens of organisms) that was cited in the original publication of the new species or subspecies, and was not excluded from being type material by the author (this exclusion can be implicit, e.g., if an author mentions "paratypes" and then subsequently mentions "other material examined," the latter are not included in the type series), nor referred to as a variant, or only dubiously included in the taxon (e.g., a statement such as "I have before me a specimen which agrees in most respects with the remainder of the type series, though it may yet prove to be distinct" would exclude this specimen from the type series).
Thus, in a type series of five specimens, if one is the holotype, the other four will be paratypes.
A paratype may originate from a different locality than the holotype. A paratype cannot become a lectotype, though it is eligible (and often desirable) for designation as a neotype.
The International Code of Zoological Nomenclature (ICZN) has not always required a type specimen, but any species or subspecies newly described after the end of 1999 must have a designated holotype or syntypes.
A related term is allotype, a term that indicates a specimen that exemplifies the opposite sex of the holotype, and is almost without exception designated in the original description, and, accordingly, part of the type series, and thus a paratype; in such cases, it is functionally no different from any other paratype. It has no nomenclatural standing whatsoever, and although the practice of designating an allotype is recognized by the Code, it is not a "name-bearing type" and there are no formal rules controlling how one is designated. Apart from species exhibiting strong sexual dimorphism, relatively few authors take the trouble to designate such a specimen. It is not uncommon for an allotype to be a member of an entirely different species from the holotype, because of an incorrect association by the original author.
In systematic botany, a paratype is defined by the International Code of Botanical Nomenclature (ICBN) as "a specimen cited in the protologue (i.e., the original description) that is neither the holotype nor an isotype, nor one of the syntypes if two or more specimens were simultaneously designated as types" (Art. 9.5).
Under this definition, paratypes are not necessarily explicitly identified as such in the original description.
Paratypes are useful in that they allow subsequent botanists to know what collections were examined by the original author and considered part of the same taxon in preparing the description of a new taxon, particularly when the holotype and isotypes may be unavailable, of poor quality, or lacking in certain details.
Paratypes are also useful in providing one or more collections from which a lectotype may be designated if no holotype, isotype, syntype, or isosyntype is extant (Art. 9.10).