International Journal of Systematic and Evolutionary Microbiology (2016), 66, 4900–4904
Taxonomic Note
DOI 10.1099/ijsem.0.001385
The nomenclatural type of the genus
Methanocorpusculum Zellner et al. 1988 and the
selection of the correct name
B. J. Tindall
Correspondence
B. J. Tindall
Leibniz-Institut DSMZ-Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH,
Inhoffenstraße 7B, 38124 Braunschweig, Germany
[email protected]
A recent Request for an Opinion has raised the issue of the inter-relationship between
Methanocorpusculum parvum Zellner et al. 1988, the type species of the genus
Methanocorpusculum Zellner et al. 1988 as defined at the time of valid publication of the genus
name and the subsequent recognition of Methanocorpusculum aggregans (Ollivier et al., 1985)
Xun et al.1989 as an earlier heterotypic synonym. Examination of the relevant literature indicates
that there are a number of misunderstandings that have arisen. In particular misinterpretation of
Rule 15 of the International Code of Nomenclature of Prokaryotes continues to be a source of
confusion. Additional problems centre on whether the nomenclatural type of a taxon continues to
be the nomenclatural type even if that name is not treated as the correct name and would not
appear in a list of names in a given classification. It would be appropriate to clarify these issues.
Oren & Garrity (2015) have submitted a Request for an
Opinion with the title ‘The correct name of the type species
of the genus Methanocorpusculum’. While such matters are
to be dealt with by the Judicial Commission and where
appropriate an ‘Opinion’ issued, background work on the
‘Request for an Opinion’ highlighted a number of issues
that suggest there are problems with the interpretation of
the wording of the International Code of Nomenclature of
Prokaryotes (Parker et al., 2015). As currently formulated
the ‘Request for an Opinion’ cannot be answered because it
combines two elements that are independent of one another
and cannot be linked. The relevant background literature is
to be found in Boone et al. (1993), Chong & Boone (2001),
Garcia et al. (2006), Ollivier et al. (1985), Xun et al. (1989)
and Zellner et al. (1987, 1989). In essence the situation is
that Methanocorpusculum parvum Zellner et al. 1988 is the
nomenclatural type of the genus Methanocorpusculum
Zellner et al. 1988, but evidence has been presented that
Methanocorpusculum parvum Zellner et al. 1988 is a heterotypic synonym of Methanocorpusculum aggregans (Ollivier
et al. 1985) Xun et al. 1989 (Boone et al., 1993; Chong &
Boone, 2001), the consequences of which are that the correct name of the taxon that includes both the type strain of
Methanocorpusculum parvum Zellner et al. 1988 and the
type strain of Methanocorpusculum aggregans (Ollivier et al.
1985) Xun et al. 1989 is Methanocorpusculum aggregans
(Ollivier et al. 1985) Xun et al. 1989. However, when this is
the case the nomenclatural type of the genus Methanocorpusculum Zellner et al. 1988 remains Methanocorpusculum
parvum Zellner et al. 1988, even if it is not treated as a correct name and not listed as a currently used species
4900
combination within the genus Methanocorpusculum Zellner
et al. 1988. The statement by Oren & Garrity (2015) that:
‘If one accepts the proposal by Boone et al. (1993), the type
species of the genus Methanocorpusculum becomes Methanocorpusculum aggregans because Rule 23a and Principle 8
dictate that there can only be one correct name applied to a
given circumscription, position and rank, and that name is
based on priority.’
is not in accordance with the wording of the Code because
there is no wording in the Code that requires the nomenclatural type of the genus to be changed if the nomenclatural
type is shown to be a later synonym of another species in
the same (or another) genus. Boone et al. (1993) also do
not make that proposal.
Similarly the wording (Oren & Garrity, 2015):
‘the correct name of the type species of the genus, as based
on Principle 8, Rules 15, 23a, 41a(2) and 42, is Methanocorpusculum aggregans, with strain MSt as the type permanently associated with this name.’
is not in accordance with the Principles and Rules of the
Code cited because while the combination Methanocorpusculum aggregans may indeed be the correct name, that does
not make it the nomenclatural type of the genus Methanocorpusculum Zellner et al. 1988.
The major misunderstanding that arises is the failure to distinguish between nomenclature (in the form of validly published
names and designated nomenclatural types) and classification
where in the case of the recognition of synonyms only one
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legitimate, validly published, later heterotypic synonym of Methanocorpusculum
parvum Zellner et al. 1988 treated as not being a correct name
legitimate, validly published, earlier heterotypic synonym of Methanocorpusculum
aggregans (Ollivier et al. 1985) Xun et al. 1989 treated as the correct name
legitimate, validly published, correct name
legitimate, validly published, correct name
legitimate, validly published, correct name
5: Methanocorpusculum Zellner et al. 1988 sensu Chong and Boone 2001
Species names used in the genus
Methanocorpusculum parvum Zellner et al. 1988
(nomenclatural type of the genus Methanocorpusculum Zellner et al. 1988)
Methanocorpusculum labreanum Zhao et al. 1989
Methanocorpusculum bavaricum Zellner et al. 1989
Methanocorpusculum sinense Zellner et al. 1989
Name not used because it is treated as a later homotypic synonym
[Methanocorpusculum aggregans (Ollivier et al. 1985) Xun et al. 1989]
legitimate, validly published, correct name
legitimate, validly published, correct name
legitimate, validly published, correct name
legitimate, validly published, correct name
legitimate, validly published, correct name
legitimate, validly published, correct name
legitimate, validly published, correct name
legitimate, validly published, correct name
legitimate, validly published, correct name
4: Methanocorpusculum Zellner et al. 1988 sensu Zellner et al. 1989
Species names used in the genus
Methanocorpusculum parvum Zellner et al. 1988
(nomenclatural type of the genus Methanocorpusculum Zellner et al. 1988)
Methanocorpusculum bavaricum Zellner et al. 1989
Methanocorpusculum sinense Zellner et al. 1989
3: Methanocorpusculum Zellner et al. 1988 emend. Xun et al. 1989
Species names used in the genus
Methanocorpusculum parvum Zellner et al. 1988
(nomenclatural type of the genus Methanocorpusculum Zellner et al. 1988)
Methanocorpusculum aggregans (Ollivier et al. 1985) Xun et al. 1989
Methanocorpusculum labreanum Zhao et al. 1989
2: Methanocorpusculum Zellner et al. 1988 sensu Zhao et al. 1989
Species names used in the genus
Methanocorpusculum parvum Zellner et al. 1988
(nomenclatural type of the genus Methanocorpusculum Zellner et al. 1988)
Methanocorpusculum labreanum Zhao et al. 1989
1: Methanocorpusculum Zellner et al. 1988
Species names used in the genus
Methanocorpusculum parvum Zellner et al. 1988
(nomenclatural type of the genus Methanocorpusculum Zellner et al. 1988)
Table 1. Time line of the changes in the nomenclature and classification of members of the genus Methanocorpusculum
Nomenclatural type of the genus Methanocorpusculum
4901
4902
legitimate, validly published, later heterotypic synonym of Methanocorpusculum
aggregans (Ollivier et al. 1985) Xun et al. 1989, treated as not being a correct name
Name not used because it is treated as a later homotypic synonym
[Methanocorpusculum parvum Zellner et al. 1988]
(nomenclatural type of the genus Methanocorpusculum Zellner et al. 1988)
6: Methanocorpusculum Zellner et al. 1988 interpretation according to the Rules of the Code
Species names used in the genus
Methanocorpusculum aggregans (Ollivier et al. 1985) Xun et al. 1989
legitimate, validly published, earlier heterotypic synonym of Methanocorpusculum
parvum Zellner et al. 1988, correct name
Methanocorpusculum labreanum Zhao et al. 1989
legitimate, validly published, correct name
Methanocorpusculum bavaricum Zellner et al. 1989
legitimate, validly published, correct name
Methanocorpusculum sinense Zellner et al. 1989
legitimate, validly published, correct name
Table 1. cont.
B. J. Tindall
validly published name must be selected in accordance with
the Rules of the Code, i.e. the correct name.
Examination of the literature indicates that although Boone
et al. (1993) recognised that Methanocorpusculum parvum
Zellner et al. 1988 and Methanocorpusculum aggregans
(Ollivier et al. 1985) Xun et al. 1989 should be treated as
heterotypic synonyms they continue to use the name Methanocorpusculum parvum Zellner et al. 1988 rather than
Methanocorpusculum aggregans (Ollivier et al. 1985) Xun
et al. 1989. The reasons are not clear from the text. However, Chong & Boone (2001) clearly state that they consider
Methanocorpusculum aggregans (Ollivier et al. 1985) Xun
et al. 1989 to be a junior subjective (i.e. a later heterotypic)
synonym of Methanocorpusculum parvum Zellner et al.
1988. The reasons are unclear, but one possibility is that the
authors applied priority to the authors of the combinations
Methanocorpusculum parvum Zellner et al. 1988 and Methanocorpusculum aggregans (Ollivier et al. 1985) Xun et al.
1989 rather than as required by Rule 23a Note 1 and Rule
42 to the respective epithets (parvum Zellner et al. 1988 vs
aggregans Ollivier et al. 1985).
Garcia et al. (2006) add further confusion by stating:
‘The high level of DNA reassociation suggests that M. parvum and M. aggregans may be subjective (i.e. heterotypic)
synonyms (Boone et al., 1993). If further investigations support this conclusion, M. aggregans would have precedence
over M. parvum, which would then have to be reclassified
as M. aggregans subspecies parvum. This reclassification
would then invalidate the genus Methanocorpusculum as
well as the family Methanocorpusculaceae.’
The current wording of Rule 15 clearly indicates that:
The [nomenclatural] type ‘is that element of the taxon with
which the name is permanently associated, whether as a
correct name or as a later heterotypic synonym.’
Proposals have been made to change this wording (Tindall,
2015a), but in essence it confirms that the nomenclatural
type of the genus Methanocorpusculum Zellner et al. 1988, is
Methanocorpusculum parvum Zellner et al. 1988. Furthermore when treated as a later heterotypic synonym of Methanocorpusculum aggregans (Ollivier et al. 1985) Xun et al.
1989 it remains the nomenclatural type. Consequently, the
genus name Methanocorpusculum and the family name
Methanocorpusculaceae are the validly published and correct
names at their respective ranks.
It is also important to emphasise that when the combination Methanocorpusculum parvum Zellner et al. 1988 is
treated as a later heterotypic synonym of Methanocorpusculum aggregans (Ollivier et al. 1985) Xun et al. 1989 and is
also treated as not being a correct name there is no wording
in the Code that makes the combination Methanocorpusculum parvum Zellner et al. 1988 illegitimate. This would also
not ‘invalidate’ either the genus name Methanocorpusculum
Zellner et al. 1988 or the family name Methanocorpusculuaceae Zellner et al. 1989.
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Nomenclatural type of the genus Methanocorpusculum
Reference to Rule 44 as given by Oren & Garrity (2015) is
the reason that if Methanogenium aggregans Ollivier et al.
1985 is considered not to be in the same genus as the
nomenclatural type of the genus Methanogenium Romesser
et al. 1981, Methanogenium cariaci Romesser et al. 1981, but
in the same genus and a synonym of Methanocorpusculum
parvum Zellner et al. 1988, the nomenclatural type of the
genus Methanocorpusculum Zellner et al. 1988, then the
consequences as proposed by Xun et al. (1989) are that a
new combination must be created, Methanocorpusculum
aggregans (Ollivier et al. 1985) Xun et al. 1989. In contrast,
if Methanocorpusculum parvum Zellner et al. 1988 were to
be considered to be in the same genus as Methanogenium
cariaci Romesser et al. (1981) then the principle of priority
applies to the names at the rank of genus and a new combination using the genus name Methanogenium would have to
be created for Methanocorpusculum parvum Zellner et al.
1988. However, if Methanocorpusculum parvum Zellner
et al. 1988 were to be considered to be a later heterotypic
synonym of Methanogenium aggregans Ollivier et al. 1985
no new combination needs to be created. However, in both
cases Methanocorpusculum parvum Zellner et al. 1988
remains the nomenclatural type of Methanocorpusculum
Zellner et al. 1988 even if that genus name were to be
treated as a later heterotypic synonym of Methanogenium
Romesser et al. 1981 and not as a correct name.
Much of the current confusion centres round the wording
of Rule 15 and the fate of nomenclatural types when they
are treated as later heterotypic synonyms. This issue arises
at regular intervals in both the incorrect interpretation
(Asakawa & Nagaoka, 2003; Chong & Boone, 2001; Lindström & Young, 2011; Losey et al., 2013; Oren & Garrity,
2015; Whitman et al., 2015) and in the interpretation consistent with the wording of the Code (Tindall, 2008, 2014a,
b, 2015b). It should however, be remembered that by
allowing a nomenclatural type that is treated as a later heterotypic synonym to remain the nomenclatural type serves
an important role central to Principle 1, ‘to aim at the stability of names.’
In order to clarify and summarise the current example Table 1
gives a time line of the changes in the nomenclature and classification of members of the genus Methanocorpusculum.
Acknowledgements
The author is employed by an organisation that commercially offers
both taxonomic services as well as biological material to the scientific
community. This may be perceived as a potential conflict of interest.
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