Holotype

A holotype (sometimes simply type) is the single physical example or illustration of an organism that defines the characteristics of the whole species. It is the definitive member of that species. Other specimens can be compared with the holotype to determine whether they are actually a member of that species. For example, the holotype for the butterfly Lycaeides idas longinus is held by the Museum of Comparative Zoology at Harvard University, and the holotype for the extinct mammal Cimolodon is at the University of Alberta. The concept of holotypes is an important part of Linnaean taxonomy.

Plants are typically dried and kept in an herbarium. They are the specimens defined as representing the taxon. A holotype may define not only a species or lower taxon, but it may also define higher taxons, eg. Cactus opuntia is the holotype for the Opuntia genus. This type species is now known as Opuntia ficus-indica. This shows that for a type species a reference is made to the relevant description.

The comparison against a holotype is often unnecessary if the organism is well-known and complete. Organisms that were described before the 19th century do not normally have holotypes. The holotype is often, but not always, the first example of the particular species that has been found because it represents the first opportunity to describe it in scientific literature. If more than one specimen was used to describe the species, then the other specimens apart from the holotype are called paratypes. However, there is sometimes a risk that a paratype is not in fact of the same species as the holotype, but a very similar one. Because of this, the description may not be accurate.

Sometimes just a fragment of an organism makes the holotype, for example in the case of a rare fossil. The holotype of Pelorosausus humerocristatus, a large herbivore dinosaur from the early Jurassic period, is a fossil leg bone stored at the Natural History Museum in London. Even if a better specimen is subsequently found, the original remains the definitive example of the species because it may eventually turn out that the new example is not of the same species. Of course, even for extant (living) species there is always the opportunity to obtain better specimens, and these are obtained all of the time and deposited in collections. These better specimens cannot replace the holotype because the ultimate purpose of the holotype is to serve as a physical reference connected to the original description.

There are many terms (see Biological types) used to describe other example specimens of a species -- such as an isotype, which is a duplicate specimen for the holotype collected in the same place and at the same time. If there is a comparative specimen of the opposite sex to the holotype then it is called an allotype. Should the holotype be destroyed or otherwise lost then a substitute specimen can be selected and which is then called the neotype.

More obscurely, if the author of the original paper describing the species did not select a holotype, then the specimens used are called syntypes. One of them may subsequently be selected as the definitive example and is then called the lectotype and the remainder become paralectotypes. For example, the mosquito Aedes refiki was described in 1928 in terms of several specimens, but the lectotype was only selected from them in 2000 reducing the remainder to the status of paralectotypes.de:Nomenklatorischer Typus