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The term "type" is tied in biological nomenclature to a very specific concept - that of a designated specifier that provides the definitive concept of a given taxon. For instance, when describing a new species, the author(s) is required to name the specimen or one of the specimens used as the type specimen. The name for the new species then becomes indelibly tied to that specimen, and should any confusion ever arise as to the identity of the species (for instance, if it turns out that two or more species have been mistaken for one, or if the published description turns out to omit some feature[s] required for identification), examination of the type specimen should (hopefully) resolve these issues. Similarly, at higher levels, each genus requires a type species, and each family requires a type genus. See for more information relevant to animals, and for plants.
A number of terms are in use to refer to different classes of types, and some of these are listed below (note that different nomenclatorial codes may differ in the terminology used):
type series: the total group of specimens used in the original description. Ideally, one specimen is the holotype and the remainder paratypes, but if no holotype has been designated, the entire type series become syntypes.
holotype: a single specimen (or illustration for the Botanical Code) designated by the author in the original publication. Under the Zoological Code since 1999, any species description that does not explicitly designate a type is deemed invalid, and the species name a .
syntype: where the original description was based on a number of specimens, some or all of them may hold equal status as type specimens. Should a syntype series turn out to contain examples of more than one species, a subsequent reviser may designate a lectotype (see below).
lectotype: a specimen selected from a syntype series to become the single name-bearing type of the species in order to confirm the identity of the species. The other previous syntypes become paralectotypes (see paratype, below).
neotype: a new type specimen designated subsequent to the original description. A neotype can only be designated if a type was not originally designated (for species published before 1999), or if the original type(s) is lost or destroyed. In a very few cases in zoological nomenclaure (such as for bauri) a neotype has been designated to replace an unidentifiable holotype - such an action, however, requires a Decision by the .
hapantotype: (Zoological Code) for protists with complex life cycles (such as ), a series of specimens taken from different stages of the life cycle acting as the type. Though composed of multiple specimens, a hapantotype series is treated as a single holotype, and a lectotype may not be designated from within it. Should a hapantotype turn out to contain specimens from more than one species, specimens may be excluded from it until only conspecific ones remain.
type strain: (Bacteriological Code) For prokaryotes, the type is not a preserved specimen, but an isolated culture. The Bacteriological Code of Nomenclature requires that cultures of the type strain be deposited in at least two separate institutes' culture stores.
paratype: Any specimens in the type series other than the holotype (or lectotype in the case of paralectotypes). Paratypes have no official status in determining species identity, but may have historical or practical significance (for instance, if the holotype does not show all the features useful in characterising the species). The term allotype is sometimes used for a paratype that represents the opposite sex from the holotype.
cotype: (Zoological Code) this term has been used in the past to refer to either a paratype or a syntype. Its use is now discouraged.
isotype: (Botanical Code) a specimen deriving from the same individual as the holotype (for instance, a second cutting from the same tree).
epitype: (Botanical Code) a specimen designated at a later date to characterise a species, where the original type material is not sufficient to do so. The original type retains name-bearing status, and should the epitype later prove not to be conspecific, the name remains with the holotype (however, it is not uncommon for the to conserve the common understanding of a name by setting aside the holotype in favour of the epitype).