Types

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Category: Types
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A scientific name is a unique and distinct identifier for a taxon. The need for such a name is trivial as a ‘Tower of Babel’ situation whereby no two persons use the same name for a taxonomic unit would obstruct efficient communication. Despite this triviality all too often multiple names have been given to the same taxon (synonyms) or, reversely, multiple taxa have been endowed with the same name (homonyms).

In order to avoid and, if already too late, resolve such name-confusions universally accepted rules for name-giving, the so-called codes of nomenclature, are used. In zoological nomenclature, the code used today is the fourth edition of the International Code of Zoological Nomenclature (ICZN, 1999).

One of the ruling principles of the ICZN is that each scientific name must be objectively defined by a name-bearing type. This typification is continuous from the family group to the species group meaning that:

  • each family-group taxon (so also, subfamilies and tribes, if existent) has a name-bearing type genus;
  • each genus-group taxon (so also subgenera, if existent) has a type species;
  • each species-group taxon (so also subspecies, if existent) has one or several type specimens.

Example - Stichopus is the type genus of the Stichopodidae; Stichopus chloronotus Brandt, 1835 is the type species of Stichopus; Stichopus moebii Semper, 1868 is one of the species in the genus Stichopus, it’s holotype is deposited in the Zoologisches Museum zu Universität Hamburg under the acquisition number ZMH E. 2702.

Types can be designated by the original author (= by original designation) or by a later author (=subsequent designation). However, a nominal species is only eligible to be fixed as the type species of a nominal genus (or subgenus) if it was originally included in the concerned genus.

Example – In 1958, Deichmann designated Holothuria sanctori Delle Chiaje, 1823 as type species of the genus Microthele Brandt, 1835. This, as Clark & Rowe (1967) correctly noted, is inadmissible since H. sanctori was not originally listed in Brandt’s Microthele. The species H. (Microthele) maculata Brandt, 1835 was subsequently (by Clark & Rowe, 1967 not by Brandt, 1835) designated as type-species. Clark & Rowe’s (1967) typification stabilised the original concept of Microthele. H. sanctori was later (Rowe, 1969) referred to a new subgenus: Platyperona Rowe, 1969.

In the species group several kinds of types exist. The type series holds all the specimens on which an author based the new species (or subspecies) name. Within the type series several categories can be recognised depending on whether they were originally (validly established in the original publication) or subsequently (validly established in a later publication) fixed.

When an author decides that he has a new species-group taxon before him he must describe and validly name it. In order to have an objective standard for the new name he must set aside one or several name-bearing types, the so-called type series that comes from the type locality, i.e. the geographical place of collection.

If in the type series none of the specimens was indicated as being the most typical for the new name, all specimens in the type series collectively constitute the name-bearing type and are called syntypes.

If an author on the other hand indicates that a single specimen is the most typical for the species, he has designated a holotype. If there are no other specimens in the type series, then the holotype is fixed by monotypy. If next, to the holotype, other specimens are present in the type series, these are called paratypes and are no longer name-bearing types.

When in the original publication none of the type-specimens was indicated as name-bearing type, one of the specimens of the type series can, in a later publication, be designated as lectotype if there’s a need to stabilize the name. The other specimens in the type series then become paralectotypes. Only the lectotype keeps its name-bearing status. If it is found later that the designated lectotype was not a syntype, it looses its status as lectotype.

When an author can prove (e.g. through annual reports of museums, through correspondence with curators,…) that no name-bearing type specimens (i.e. holotype, lectotype, syntype or prior neotype) exist, he can designate a new name-bearing type from approximately the same locality as the original type locality: the neotype. However, neotype designation is not to be taken lightly, it can only be done if there’s an exceptional need, e.g. to clarify the taxonomic status or the type locality.