principles of systematics and nomenclature general system and phylogeny of insects systematics of Ephemeroptera

the Dual Nomenclature System is a component of Cladoendesis — method of reconstructing phylogeny

Web version of the division "General nomenclatural principles" from the paper by 

N.J. Kluge

Circumscriptional names of higher taxa in Hexapoda

Bionomina, No.1: 15-55

(language improvement by V. Belov)


Table of contents:

General nomenclatural principles

1. Typified vs. circumscriptional names

2. Type-based nomenclatures

2.1. Type-based rank-based nomenclatures

2.2. The type-based hierarchical nomenclature

2.3. Another type-based nomenclature

3. Circumscription-based nomenclatures

3.1. The circumscriptional nomenclature

3.1.1. Availability of circumscriptional names

3.1.2. Assigning circumscriptional names to taxa

3.1.3. Validity of circumscriptional names

3.2. Other rules for circumscription-based names

4. Nomenclatures other than type-based and circumscription-based

Application of circumscriptional nomenclature to high-level insect taxa — see Kluge 2010 in "Nomina Circumscriobentia Insectorum"



1. Typified vs. circumscriptional names

Since pre-Linnaean times, two alternative approaches to naming taxa have been in general use — the typebased and the circumscription-based. The two are mutually exclusive, and a name can be used according to one of them only. A classification may either stick to one of these approaches, or use both concurrently by applying different approaches either to names of different taxa or to different names of the same taxon. Numerous examples of how this worked on various arthropod classifications since 1758 are given in my online catalogue Nomina Circumscribentia Insectorum, where typified (i.e., type-based) and circumscriptional (i.e., circumscription-based) names are marked “T” or “C” in colored squares, respectively. What makes the two alternative approaches coexist is the general language-related challenge: to communicate meaning unequivocally, a name must be uniquely associated with an object, but the number of objects to be named is unlimited, whereas the human memory can only handle a limited number. Circumscriptional nomenclature gives each taxon a unique name but cannot provide enough names to cover all the taxa. Typified nomenclature is capable to name any number of taxa, but the names are not unique: depending on classification, the same typified name can be applied to different taxa; this allows to minimize the number of names. The situation may dictate what kind of name (circumscriptional or typified) to chose for a given taxon. Low-rank taxa (numerous and often known to a small number of specialists) usually get typified names, whereas high-rank taxa (which are fewer and often widely known) get circumscriptional names. Each approach has its advantages, and attempts to impose a single type of nomenclature have been unsuccessful.

A solution I suggested is my versatile Dual Nomenclature System (Dual-Nom) that takes advantage of both type-based and circumscription-based names (Kluge 1999a, b, 2000, 2004a, 2009a). The basic principle of Dual-Nom is applying two sets of rules to different sets of names, with no name subject to both. Dual-Nom includes circumscriptional nomenclature (Circ-Nom) and hierarchical nomenclature (Hier-Nom), treating any non-typified name as circumscriptional (see 3.1) and any typified name as hierarchical (see 2.2). The typified names can also be treated as rank-based; thus, Dual-Nom is compatible with the International Code of Zoological Nomenclature (the Code) and the Rohdendorf-Rasnitsyn nomenclature for higher taxa (see 2.1). Under Dual-Nom, a taxon may have two valid names: a typified hierarchical name (available for every taxon) and a non-typified circumscriptional name.

Hemihomonyms (term coined by Starobogatov 1991) are identical names given to obviously different taxa under different nomenclatures — unlike true homonyms, i.e., identical names applied to different taxa within a single nomenclatural system. Thus, a given nomenclature can get rid of homonyms by applying its rules, but hemihomonyms cannot be totally eliminated, since no rules operate across nomenclatural lines. In cases where hemihomonyms cause confusion we have to come up with a solution.


2. Type-based nomenclatures

All the type-based zoological nomenclatures deal with the same set of typified names whose availability is determined under the Code. Spelling and usage of typified names may differ between rank-based nomenclatures (see 2.1), the hierarchical nomenclature (see 2.2) and other type-based nomenclatures (see 2.3). The typified names can also be used in a basic format (Kluge 2009a).

The basic format (or “universal form”) is a non-italicized genus-group name (as defined by the Code) followed by slash and the letter(s) “f” (where a family-group name derived from that generic name is available) and “g” (to indicate availability as a genus-group name). The authorship can be added in brackets as necessary. Examples of basic format are:  “Ephemera/fg”; “Ephemera/fg [f: 1810; g: 1758]”; “Ephemera/fg [f: Ephemerinae Latreille, 1810: 273; g: Ephemera Linnaeus, 1758: 546, typus E. vulgata Linnaeus, 1758 (design. Latreille 1810)]”. This format covers the entire set of typified names for any supra-specific taxa that include Ephemera vulgata but no type species of any genus- or family-group names older that Ephemera and Ephemerinae, respectively — i.e., the genus Ephemera, the subfamily Ephemerinae, the family Ephemeridae, the order Ephemerida, the infraclass Ephemerones, etc.

For names introduced in the same publication, page priority shall apply. Thus, the name Ephemera Linnaeus 1758 (genus 208, p. 546) is younger than Libellula Linnaeus 1758 (genus 207, p. 543) but older than Phryganea Linnaeus 1758 (genus 209, p. 547).

The oldest typified names in zoology are Araneus and Araneidae (for genus- and family-groups, respectively), both arbitrarily deemed to have been published by Clerck on 1 January 1758, prior to the 10th edition of the Systema Naturae (ICZN 1999, Kluge 2007c, ICZN 2009). Accordingly, the basic format for a typified name of any zoological taxon that includes the type species of Araneus (e.g., Metazoa, Arthropoda, Chelicerata) would be Araneus/fg. Any taxa that do not include the type species of Araneus but include the type species of Scarabaeus (e.g., Mandibulata, Hexapoda, Pterygota, Metabola) have the basic-format typified name Scarabaeus/fg, because Scarabaeus Linnaeus 1758 (genus 170, p. 345) is the first arthropod genus described in the 10th edition of the "Systema Naturae", and the ordinal name Scaraboides Laicharting 1781 (p. II) is the first typified name proposed for arthropods.


2.1. Type-based rank-based nomenclatures

Typified botanical names of any rank are regulated by the International Code of Botanical Nomenclature. The International Code of Zoological Nomenclature regulates type-based zoological names from subspecies to superfamily level, whereas the names of higher-rank taxa are not subject to any generally accepted rules. Various sets of universal rules for typified high-rank names have been suggested by several authors.

The most rational set of such rules (Rohdendorf 1977, Rasnitsyn 1982) treats the names of taxa above superfamily as family-group names. This approach was applied to a good number of insect taxa (Rohdendorf & Rasnitsyn 1980, Rasnitsyn & Quicke 2002). Other suggested rules for typified names (Starobogatov 1991, Alonso-Zarazaga 2005) recognize several nomenclatural groups above the family group; they are less convenient and have not been tested.

All the type-based nomenclatures mentioned above are also rank-based (following ranking). 

Suggestions have been made to use some non-typified names as rank-based ones (e.g., Bey-Bienko 1962, Boudreaux 1979). Using non-typified names as rank-based is hardly reasonable, since the pool of typified names can fully satisfy any demand for rank-based names (Kluge 1999a, b, 2000). Most taxonomists consider the concept of rank above species level to be purely artificial. Because of this, some workers would prefer to get rid of supra-specific ranks altogether. A solution is offered by hierarchical nomenclature.


2.2. The type-based hierarchical nomenclature

The Code-based hierarchical nomenclature is the only rank-free system of typified names (Kluge 1999a–b); this nomenclature is a part of Dual-Nom, which is totally rank-free.

Hierarchical name (nom.hier.) is derived from the basic-format typified name (see 2.) by adding a number to indicate the place of the taxon within a hierarchical classification, with “1” assigned to the highest taxon to which the typified name can be applied, “2” to its immediate subordinate, and so on. The numbers are not associated with any formal ranks and can be used in classifications where no such ranks exist. For example, the taxon that includes all mayflies and their extinct relatives is named “Ephemera/fg1” whether it is an infraclass, a superorder, an order, or has no formally assigned rank.

To make the typified names easier to understand, the oldest genus-group names of the nearest excluded and included groups can be added in parentheses behind the numbers or instead them. For example, the name “Scarabaeus/fg4 (sine Podura; incl. Lepisma),” or simply “Scarabaeus/fg (sine Podura; incl. Lepisma)”, refers to the Amyocerata, the insect taxon that does not include the Entognatha (whose oldest genus-group name is Podura) but does include the Triplura (whose oldest genus-group name is Lepisma).

Unlike the Code-regulated rank-based names, the hierarchical names are not bound by any formal (i.e., artificial) ranks. Any supra-specific taxa in any classification can be given hierarchical names, flexible and unique as they are (whereas in rank-based nomenclatures only taxa with formal ranks can be named). In addition, some taxa can also bear circumscriptional names (see 3.1).

The rank-free hierarchical nomenclature has proven practical. It allowed me to thoroughly describe and compare several hundreds supra-specific mayfly taxa, most of which could not be named within the traditional rank-based nomenclature (Kluge 2004a, Kluge 2007a, b, 2008, 2009b, c, 2010a, b).


2.3. Another type-based nomenclature

Papavero et al. (2001), unaware of the hierarchical nomenclature, suggested another type-based nomenclature, similar but not completely rank-free: names are numbered starting from the lowest taxon of each formal rank rather than from the highest taxon. The highest taxon is defined objectively within a classification, while the lowest one is not (it can be only defined artificially, i.e., using artificial absolute ranks). Papavero’s nomenclature was developed as a concept and was not tested; it is clearly less practical than the hierarchical one.


3. Circumscription-based nomenclatures

Besides typified names (see 2.), zoologists use today a lot of non-typified ones: most agree that we can’t do without names like Metazoa, Arthropoda, Hymenoptera or Apocrita. Non-typified names can be used in two different ways: (1) merely following tradition and/or authority, with no general rules, or (2) applying the rules of circumscriptional nomenclature. The first way is practical where one has to deal with a very limited number of taxa anybody can easily memorize. It works well for high-rank taxa in studies of low-rank taxonomy and for non-taxonomic publications — but becomes all but impossible to use as scores of names begin to overwhelm the memory. This often happens when one is facing the task to name all the lineages that a reconstructed phylogeny reveals or suggests. In such cases it is advisable to use non-typified names following special rules of circumscriptional nomenclature.


3.1. The circumscriptional nomenclature

Rules regulating non-typified zoological names have been proposed earlier (Kluge 1996a, 1999a–b, 2000). This circumscriptional nomenclature (Circ-Nom) constitutes a part of the Dual-Nom (see 1.). As well as the whole Dual-Nom, the Circ-Nom is theory-free: the same circumscriptional name can be used in multiple mutually contradicting classifications no matter what the taxon’s nature is perceived to be (holophylum, plesiomorphon, collective group or anything else). The taxon with a circumscriptional name can be variously ranked (unlike in rank-based nomenclatures), variously placed within classifications (unlike in hierarchical nomenclature), or variously defined in morphological terms. However, a circumscriptional name can never be applied to a taxon of a different circumscription.

The circumscriptional nomenclature had been successfully tested on taxa above Arthropoda, on higher arthropod taxa, on higher insect taxa, and at all levels within the Ephemeroptera (Kluge 2000, 2004a, b, 2005a,b, 2008, 2010a, 2004–2010). Its application to higher insect taxa is illustrated and discussed below.

The basic principles of circumscriptional nomenclature are as follows:


3.1.1. Availability of circumscriptional names

A name available as circumscriptional is any zoological name that is not part of the species group, genus group or family group defined by or subject to the Code, and is not obtained by adding suffix and ending to an available genus-group name. The “-morph-” and “-form-” elements are often used to produce typified names and therefore should be treated as suffixes, so the names produced by adding “morph-” or “-form-” to generic names are not available as circumscriptional. Names of species-, genus- and family-groups are regulated by the Code on principles of typified nomenclature, incompatible with circumscriptional principles, so the two sets of names should never be confused. Any names produced using the family-group model should also be subject to the rules of typified nomenclature, but not circumscriptional nomenclature.

Circumscriptional zoological names shall have the same starting point (1758) as Code-regulated typified ones: it is the availability of the typified names that allows to distinguish the two sets. In a circumscriptional name, any emendation (including those that affect suffixes and endings only) gives rise to a new circumscriptional name with its own author, date and original circumscription (unlike circumscriptional names, typified names have changeable suffixes and endings). 

Under the Code, a name is not available unless originally proposed in latinized form. In circumscriptional nomenclature, though, an exception should be made — at least for the names introduced by early French authors, since great many circumscriptional names currently in extensive use were originally proposed in French only, including Hexapoda Blainville 1816 (originally “Hexapodes”), Isoptera Brullé 1832 (“Isoptères”), Heteromera Duméril 1805 (“Hétéromères”), Rhopalocera Duméril 1805 (“Ropalocères”), Diplopoda Gervais 1844 (“Diplopodes”), etc. Attributing those to the workers who were the first to latinize such names would cause confusion, as those workers did not see themselves as the authors and thus mentioned no such authorship in their papers. So these names should be considered available in the latinized form but with the authorship and date of the original French spelling.


3.1.2. Assigning circumscriptional names to taxa

In circumscriptional nomenclature, the name-bearing type is the whole set of taxa listed in the original publication.

The attributes that define a circumscriptional name are (Kluge 1996a):

Original included membership: the set of species explicitly or implicitly quoted in the original publication of the name as members of that taxon.

Original net included membership: original included membership less (1) the species whose position is considered uncertain in the original publication, and (2) the species erroneously listed as members of the taxon contrary to the diagnosis provided for that taxon in the original publication (see Lepidoptera).

Original excluded membership: a set of species explicitly or implicitly quoted in the original publication of the name as non-members of that taxon. Original net excluded membership: original excluded membership less (1) the species whose position is considered uncertain in the original publication, and (2) the species erroneously listed as members of another taxa contrary to the diagnoses provided in the original publication.

Original circumscription (or original admissible membership): any set containing all species of original net included membership and no species of original net excluded membership. 

The main principle of circumscriptional nomenclature is that each name should be applied only to a taxon whose circumscription fits the original circumscription of that name, i.e., which includes all species of original net included membership and no species of original net excluded membership. For this purpose, only the original publication is relevant; later publications that redefine the taxon are not.

Newly discovered species may complicate the classification, so the original circumscription would fit more than one subordinate taxon within the classification. This means that the name non-monosemantically (non-univocally) fits each of these taxa in circumscription. In such cases, each of these taxa can be given an additional younger valid name of appropriate unique circumscription, i.e. a monosemantically (univocally) fitting name. Thus, in certain situations a taxon may have more than one valid circumscriptional name (see Ephemeroptera, Odonata, DermatopteraPandictyoptera).

Different names whose original circumscriptions fit the same taxon, are termed circumscriptionalsynonyms (syn.circ.). Circumscriptional synonyms can be monosemantic (univocal) if the original circumscriptions fit the same taxon in all classifications, or, otherwise, non-monosemantic (non-univocal). Circumscriptional synonymy is quite different from ranking synonymy that may exist in rank-based nomenclatures only (in hierarchical nomenclatures, no subjective synonyms exist) (Kluge 2000).


3.1.3. Validity of circumscriptional names

If a taxon has more than one monosemantically fitting circumscriptional name, one of them should be chosen. This can be done basing on priority. Unlike the absolute requirement to fit the original circumscription, priority is optional (but desirable). There are cases where choosing a junior name over the oldest one allows to
keep tradition or avoid homonymy, hemihomonymy or other inconvenience. In some cases, choosing a single valid circumscriptional name may not be necessary and more than one circumscriptional synonym may be allowed to circulate.

Homonymy of circumscriptional names should be avoided wherever possible, but there is no strict rules about homonyms. Homonymy rules could be introduced if a general catalogue of circumscriptional names was available, but the existing catalogue covers the arthropods only (see Nomina Circumscribentia Insectorum).


3.2. Other rules for circumscription-based names

Dubois (2005, 2006, 2007) has suggested different rules for using non-typified names according to their circumscription (“bidirectional ostension”) without, however, pointing any advantages his system may have over Circ-Nom. Unlike the rank-free Circ-Nom, Dubois’s nomenclature is partly rank-dependent, being restricted to the “class-series”, i.e., taxa whose ranks are higher than superfamily. Unlike Dual-Nom, where names of any supra-species ranks can be either typified, or circumscriptional, Dubois suggests to separate typified and circumscriptional names along formal rank lines, so that names up to superfamily are typified and above that level, circumscriptional. This requires a formal line drawn between the family-group (“familyseries”) and the higher group (“class-series”). As long as the starting point for all names is 1758, and the family group as we understand it did not emerge before 1802, such line may prove hard to draw; the current Code does not make such distinction. Since Dubois also suggests that all the high-rank names (including those derived from available generic names) be subject to the circumscriptional principle, he defies any rules for typified names of high-rank taxa (see 2.). Plans to have circumscriptional principles eventually apply to all names (Kluge 1996a, Dubois 2007) should be abandoned as unrealistic (Kluge 1999a).

The “Rule of Taxonomic Consistency” (Dubois 2006: 228) disqualifies names originally proposed for families from being valid circumscriptional names, which would make unavailable many generally accepted non-typified names traditionally used as circumscriptional: e.g., Pedipalpi Latreille 1806, Chilopoda Latreille 1817, Saltatoria Latreille 1817, Siphunculata Latreille 1825 and Megaloptera Latreille1802 were originally proposed for families and are now treated as suborders, orders or classes.

Dubois’s availability rule states that a name “must have been published ... for a taxon (not an informal group)”. This means that a taxon being originally proposed with no formal rank would render its name unavailable. Applying this rule would make automatically unavailable any names introduced by Hennig and his followers, as well as many other widely used names, such as Bilateria Haeckel 1874, Pterygota Gegenbaur 1878, Metabola Burmeister, 1832 or Holometabola Burmeister 1835.

Dubois (2006: 228) suggests that “Unavailable nomina ... are not to be considered as originally included or excluded” — thus missing an important point: it is taxa, not names, that should be included or excluded. He suggests detailed formal rules defining what should be considered originally included and originally excluded taxa. However, the variety of real-life situations and ways whereby the existent non-typified names may have been originally defined is such that no set of formal rules, however elaborate, could possibly cover all. Therefore, in each case we have to use any means available to find out which animals the author of the name meant to include or exclude while drafting the original paper.

Dubois (2006: 190) oddly defines homonymy as applying the same name to taxa once considered identical but now considered different under the new circumscriptional rules. This means that every time someone keeps an old name for a taxon but changes its circumscription, the name becomes a new name with its own authorship, date and original circumscription, and a junior homonym of the old name. Applying such concept would result in an exorbitant number of names and make cataloguing impossible; workers who used names inconsistently with the rules introduced later, would be unaware of their authorship of the “new” names. Under Circ-Nom, on the other hand, applying the same name to taxa of different circumscription is regarded to be wrong, but does not create new “homonyms”.

The “Rule of Preoccupation” (Dubois 2006: 229), whereby any names “derived from the same root” are considered homonyms, would severely restrict the pool of possible names and eliminate such widely used names as Eumetazoa (derived from Metazoa) or Mecopteroidea (from Mecoptera). Under Circ-Nom, circumscriptional homonyms have the exact same spelling, just like genus-group names under the Code: it is important for both groups to keep as many non-homonymous names as possible.

To perpetuate traditional usage of non-typified names, Dubois (2006: 230) suggests special rules for ten name categories. Criteria of these categories include usage of names in both Latin and vernacular form in all languages in all systematic, non-systematic and non-scientific publications since 31 December 1899, an arbitrarily chosen date. Not only reviewing all that literature is unfeasible, but at least some criteria are hopelessly impracticable. Particularly, no “symphonym” (a name used as valid by everybody in all publications since 1899) is viable: a single paper applying standardized formats and making the nomenclature typified top to bottom (such as papers by Rasnitsyn 1982, Starobogatov 1991, or Alonso-Zarazaga 2005) would invalidate all the non-typified names at once. Besides, in non-systematic and non-scientific literature there are things no rule can cover. Under Dubois’s rules, name validity strongly depends upon current usage, which is a recipe for perpetual name change. On the other hand, under the Code, the Dual-Nom, and other nomenclatural systems, the name validity, once established, stays until the classification changes.

Dubois’s elaborate code is designed primarily to conserve widely used names, although all it takes to successfully use those is common sense: they simply don’t need to be regulated, just as vernacular names. On the other hand, the Circ-Nom (and the Dual-Nom in general) aims to ensure consistent usage of scientific names, which are too numerous and at most having too small number of users to be managed based on common sense alone.

Dubois (2006: 233) says that the transition to his nomenclature would involve every name being validated, i.e., require nomenclatural acts. On the other hand, Dual-Nom requires no extra nomenclatural action to become fully operative.


4. Nomenclatures other than type- or circumscription-based

Nomenclatures have been suggested on principles other than type-based or circumscriptional-based. Among them we can mention character-based and phylogeny-based principles.

There are names originally proposed as character-based. For example, the names Collembola Lubbock 1873, Oligomerentoma Krausse & Wolff 1919, Protomorpha Handshin 1952 and Podura Bey-Bienko 1962 have all been proposed for obviously the same taxon to reflect its various characters — ventral tube, reduced segmentation, assumed primitive condition and furca, respectively. Such a way of naming has no perspectives, since every taxon has any number of features, none more important than others. Under Circ-Nom, all these names are circumscriptional synonyms (see 3.1).

(1) The phylogeny-based principle is used in the PhyloCode (Queiroz & Gauthier 1990, Cantino & Queiroz 2010). At least three aspects make it unacceptable:

(2) It provides no general availability (or “establishment”) rules for its names, which could separate available PhyloCode names from others. So, to have a PhyloCode name established it has to be registered into the special database managed by the special committee and to get a registration number. If numbers could be really unique and distinct, names could be substituted by these numbers, and any nomenclature would become unnecessary, but this is not so.

(3) The PhyloCode is inconsistent with the International Code of Zoological Nomenclature and the International Code of Botanical Nomenclature — a major reason why most biologists who are aware of the PhyloCode reject it.

Unlike other nomenclatures, the PhyloCode is not theory-free — which is, in my opinion, the main reason why it should be rejected, even if there were no other reasons.

Should any names be established under the PhyloCode, they should be treated as either circumscriptional (see 3.1) or typified (see 2.), depending on their format.



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