General
Articles and Nomenclatural Notes with
the following titles were published on
30 September 2002 in Volume 59, Part
3 of the Bulletin of Zoological Nomenclature
Copies
of these General Articles and Nomenclatural
Notes can be obtained free of charge from
the Executive Secretary, The International
Commission on Zoological Nomenclature,
c/o The Natural History Museum, Cromwell
Road, London SW7 5BD, U.K. (e-mail: iczn@nhm.ac.uk).
General
Article (see Comments BZN 60:1, 60:2, 60:3, 61:1, 62:1)
Neotypification
of protists, especially ciliates (Protozoa,
Ciliophora)
Wilhelm Foissner
Universität Salzburg, Institut für
Zoologie, Hellbrunnerstrasse 34, A-5020 Salzburg,
Austria
Abstract. Historically,
most soft-bodied species of heterotrophic
protists (Protozoa) have been difficult to
preserve and consequently lack type material
that can be re-investigated. This causes
taxonomic and nomenclatural problems and
increases the degree of subjectivity in the
identification of these organisms. There
are hardly any ciliate species whose identity
has not been queried, or will be disputed
as new data become available. However, recently
methods have been developed that allow ciliates
(Ciliophora) to be preserved in a way that
allows type material to be preserved and
re-examined. The current paper proposes that
ciliate species are accurately re-described
and neotypes designated that can be preserved
using the new methods. The paper also proposes
that the Commission should consider waiving
Article 75.3.6 of the Fourth Edition of the
International Code of Zoological Nomenclature
(1999) in relation to ciliates and other
groups of protists and small Metazoa. This
Article states that neotypes should be designated
from specimens that come as near as practicable
from the original type locality. The reasons
why the Article should be waived for these
organisms are discussed.
Keywords. Nomenclature;
taxonomy; Protozoa; Ciliophora; protists;
ciliates; neotypification; type locality.
Introduction
This paper aims to stimulate discussion about the absence of or inadequate
quality of type material for protists, especially ciliates (Protozoa, Ciliophora).
To date, this important problem has been largely ignored by the scientists
concerned and by the scientific community in general. The lack of interest
in protist nomenclatural problems is illustrated by the low number of relevant
cases published in the Bulletin of Zoological Nomenclature and an
ignorance of the International Code of Zoological Nomenclature displayed in
recent publications by protozoologists. There are probably two main reasons
for this: (i) there are very few people studying these minute organisms and
even fewer are interested in their alpha-taxonomy and nomenclature, and (ii)
there is a lack of type material, which causes nomenclatural problems and leaves
identification extremely subjective. Similar problems exist in most ‘microfaunal’ groups
and even more severely in the nematodes (Nematoda).
Inadequate type
material
The lack of type material is the result of historical problems with the
preservation of ciliate specimens and more than 90% of all described ciliates
lack type material. Where it does exist, species are often represented by material
that fails to shows the diagnostic features. Further, in some cases material
is difficult to obtain because it is deposited in private collections (see
Foissner & Pfister, 1997).
The lack of type material is one of the most difficult problems facing
protozoologists involved in ciliate or other protozoan alpha-taxonomy. There
are innumerable examples of poorly described species, doubtful identifications,
and problematic redescriptions. Although my own research group may recognize
a thorough redescription as ‘authoritative’, others may not. Berger
(1999), for example, assigned Onychodromopsis flexilis Stokes, 1887,
accurately redescribed and neotypified by Petz & Foissner (1996), to Allotricha,
a genus and species which has never been illustrated or accurately described.
Obviously, in the absence of reliable type material, no consensus can be reached
and ciliate identification and nomenclature must remain a matter of choice.
Improved methods
for preserving ciliates
At present, most ‘modern’ ciliate
types are deposited at two centres: the Smithsonian
Institution in the U.S.A. (Corliss, 1972;
Cole, 1994) and the Biology Center of the
Museum of Upper Austria in Linz (Aescht,
1994). In the last 30 years, protozoologists
have developed improved methods for preserving
these soft-bodied organisms, allowing reliable
type material to be obtained and preserved.
Specimens are impregnated with silver nitrate
and/or protargol (known as infraciliature
or the silverline system) to show the arrangement
of somatic and oral cilia, which are among
the most important features in ciliate alpha-taxonomy
(Foissner, 1991). Under certain circumstances
other methods such as the Feulgen reaction
are used to examine the main features in
the nuclear apparatus.
Usually, light- and/or electron-microscopical micrographs and molecular
data alone are not sufficient for description of species, but may add important
additional data to the information available from conventional (silver) preparations.
The methods needed will depend on the group of protists under consideration.
What is important is that the feature(s) mentioned in the description can be
seen in the designated type material. Often several ‘holotype specimens’ might
be necessary because not all features can be seen in a single specimen or preparation.
Here, the concept of the hapantotypes can be applied (Article 73.3).
A solution to taxonomic
and nomenclatural difficulties in the ciliates
Many protist taxonomic
and nomenclatural problems could be solved
by the provision of type material using the
new methods described above. The present
practice of using illustrations as holotypes
does not solve the underlying problem because
these illustrations often cannot be examined
to reveal new data when an existing description
is found to be incomplete or inaccurate.
Further, features which are considered as
unimportant at the time of description may
later become decisive taxonomic characters
for comparison with new species. Neotypification
is the one way to overcome these and related
problems and to bring stability in ciliate
taxonomy and identification. This was emphasized
by Corliss (1972), who established some neotypes
for ‘difficult’
ciliates in the sixties. Likewise, Medioli & Scott
(1985) established neotypes for some testate
amoebae.
Generally, however, neotypification has not been practiced widely in
the protists. It was only recently that my own research group adopted this
valuable approach to clarifying protist taxonomy and nomenclature (Foissner,
1997, 1999b; Foissner & Brozek, 1996; Foissner & Dragesco, 1996; Foissner & Kreutz,
1996; Petz & Foissner, 1996). However, it is a practice that several specialists
have since followed (Agatha & Riedel-Lorjé, 1998; Petz et al., 1995;
Song et al., 2002).
Neotypification is especially useful when:
(1) no type material is available (holotype
specimen and hapantotypes (see Article. 73.3)),
but identification of the taxon is comparatively
straightforward;
(2) type material is available, but too poorly
preserved for the diagnostic features to
be recognizable. This situation may need
to be referred to the Commission;
(3) the original description is so incomplete
and/or based on so few specimens that any
identification becomes a matter of arbitrary
judgement. Alternatively, such descriptions
could be considered as referring to species
indeterminate. However, this would greatly
increase the number of scientific names because
many original descriptions of ciliates are
very incomplete. We prefer, where possible,
to identify our taxa in relation to previously
described species, and to redefine these
species by detailed redescriptions. We ensure
that the redescription is based on material
which shares at least one main distinctive
feature of the original material;
(4) it has been argued that the species has
one or more subjective synonyms. This indicates
that the taxon has a questionable identity
in the literature and, in the absence of
type material, creates a ‘classical’ justification
for neotypification;
(5) there are several similar species whose
identity will be fully differentiated by
neotypification;
(6) there are competing re-descriptions for
a taxon.
Article 75 of the
Code
Most of the neotypes
that my group has designated are in accordance
with Article 75 of the Code. However, as
protists form resting cysts, have a wide
geographical distribution, and often lack
any type material (Corliss, 1993), it is
sometimes difficult to designate neotypes
that fully satisfy Article 75. In some cases
our ciliate neotype designations do not comply
with Article 75.3.6 as they were not collected
from or near the type locality. As such,
these and similar neotypifications could
be considered to be invalid. However, we
do not consider Article 75.3.6 to be relevant
to protist neotypes for the following reasons:
(1) most ciliates and protists
are cosmopolitan, at least at the morphospecies
level (Finlay et al., 1996; Foissner, 1999a).
In addition, many are symbionts, commensals,
or parasites of metazoan animals that often
have a much wider biogeographical distribution
than the narrow definition of ‘type
locality’
implies;
(2) the existing uncertainties
can be overcome only by making types universally
available to protozoologists. The improvements
in protist taxonomy that neotypification
produces far outweigh the possible danger
of misidentified neotypes that can occur
from specimens selected out of original type
locality;
(3) as there are only a
few alpha-taxonomists working with ciliates,
it is difficult for them to obtain neotype
material from or near the type locality.
The application of Article 75.3.6 could prevent
neotypes from ever being designated;
(4) the likelihood of re-discovering
ciliates and other protists at a certain
locality is not guaranteed because the organisms
may be in a dormant (cystic) stage for most
of their life and laboratory cultivation
is often unsuccessful.
Conclusion
To sum up, I suggest that neotypes of protists, especially ciliates should
be freed from the type locality regulation of Article 75.3.6 of the Code, provided
that neotypification is based on a thorough re-description of the organism
and useable neotype material has been deposited in an acknowledged repository.
In addition, existing neotypes that have already been designated from other
than original type localities should be validated by the Commission.
Acknowledgements
I thank David Patterson (Australia),
Michael Dolan, John Corliss, Neil Evenhuis
(U.S.A.) and Andrew Wakeham-Dawson (Commission
Secretariat, London) for helpful comments
on an earlier draft of this paper.
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