What is a Type?
Type specimens are the individual specimens from which a new species or subspecies is first described and given a new scientific (“Latin”) name. The name, and that of its author, with the date of first publication, remain fixed to those objects.
This concept is central to the rules governing the scientific names of animals, as set out in the International Code of Zoological Nomenclature, or The Code. These have applied universally since the late 19th century, and are designed to ensure stability and consistency in the use of scientific names. English and other “common” names do not have types, and are unregulated by a code.
Very often, a new species is based on more than one specimen. Collectively these specimens are known as the type series, or the type material. No-one, even the species’ own author, can later add material to a type series. However, a type series is often spread across more than one collection, if the author gave, sold or traded specimens to other collectors.
Type material is usually considered among the most scientifically and historically valuable material in a natural history collection.
The type specimens of most mollusc species are empty shells, many over 100 years old. For others (including molluscs which lack shells, such as sea slugs) parts of the soft body were used.
We have verified the type status of all material featured in this project. Some previously unrecognised type material was found in the collections. Conversely, some specimens suspected of being type material proved not to fit the criteria.
The term type should not be confused with species, kinds, or forms of molluscs. In older collections, the word “type” may appear on labels as a shorthand for “typical” in its everyday sense. The terms type species and type [variety] may also appear. However, these do not denote type material, or even any association with the author of the species.
Type material retains its type status regardless of what happens to the attached name. Subsequent research often concludes that a species has been described as new more than once. According to the Code, the oldest name is to be given priority over newer ones, which become synonyms of it.
Many types are therefore the types of names that are now considered synonyms. This is particularly the case in groups in which species are very variable or geographically widespread. However, further research frequently concludes that synonyms should in fact be considered species, or subspecies, in their own right. As old names, they remain available to be used and retain their priority.
Different categories of types
If, at the time of description, an author has only one specimen, or clearly indicates which specimen should be considered the name-bearing type, it is known as the holotype. Any other type specimens are known as paratypes.
If no holotype was indicated, all the type specimens are syntypes and have equal status. Most 19th century Mollusca types are syntypes.
Sometimes it is later necessary to select one syntype as the name-bearing type. This then becomes a lectotype and the other syntypes become paralectotypes. This lectotype designation needs to have been published to be valid. Some collections contain shells with labels suggesting they are lectotypes, but they remain syntypes until this is published.
Types are irreplaceable if lost or destroyed. However, under certain strict conditions a single neotype may be designated in a publication, from among suitable material.
The term primary type is sometimes used for holotypes, syntypes, lectotypes and neotypes, because they are the name-bearing specimens, i.e. those to which the name is fixed. By definition, paratypes and paralectotypes lack this status.
The geographical location at which type material was found or collected is known as the type locality (or localities, in the case of syntypes from several locations). The terms topotype, hypotype and homeotype, which we encountered in collections, do not denote type material. Nevertheless, such specimens may be useful in research. A topotype is a specimen collected at the type locality, potentially many years later. A hypotype is a specimen cited or figured in a subsequent publication. A homeotype has merely been compared to a type.
Inference of holotype (Article 74.6)
Holotypes are less common in older collections than labels or revisionary papers may suggest. Throughout this database, we have attempted to apply the following ICZN criteria on holotypes and lectotypes.
Under the Code, a holotype may only be fixed in the original publication and by the original author. The existence of a holotype (rather than a series of syntypes) can be subsequently inferred only when there is evidence that the author used only one type specimen. This is known as a holotype fixed by monotypy (ICZN, Art. 73.1).
However, numerous later workers have inferred or assumed that certain favoured or labelled “type” specimens were the holotypes of their species, whether or not such workers were then aware of the existence of additional syntypes. The Code now recommends that this assumption of holotype is avoided (ICZN, Recommendation 73F).
When such an assumption or inference of holotype has been published, before the year 2000, it is to be considered a lectotype designation by that worker (ICZN, Art. 74.1). This has happened on numerous occasions, meaning that many types in collections with labels reading “holotype” should properly be considered lectotypes.
It follows that any “paratypes” associated with the original “holotype” are in fact paralectotypes.