NOMENCLATURE AND CLASSIFICATION OF ORGANISMS
XIX
plant or animal kingdom, except on an arbitrary and artificial basis.
Certain organisms, furthermore, are classified as both plants and animals; i.e., Euglena, Volvox, etc. For convenience only, the green
flagellates of the Protozoa and their colorless counterparts are best
placed in the Euglenophyta or Chlorophyta, leaving the more highly
specialized colorless flagellates in the Protozoa. Most of the interrelationships between these groups of microorganisms are quite indistinct,
indicated by the dashed lines, but it is felt that any grouping of the
algae and fungi in one group, the Thallophyta, is highly artificial, and
that they represent many separate stocks that have been evolving independently for a long time.
Such a phylogenetic chart can be used as a guide to examples of
parallel or convergent evolution occurring in these major evolutionary
lines. For example, any morphological or biochemical characteristic
found only in the Mammalia and Insecta is probably the result of an
independent origin in the two groups, while a characteristic found in
all the main Chordata and none of the phyla along the main line leading to the Arthropoda would presumably have originated once sometime after the separation of the two groups indicated by the fork. The
step-by-step loss of morphological and biochemical characteristics
along any one line is possible, and a simple structure or function may
be the result of reduction rather than a result of a primitive condition.
The major phyla or divisions in the plant and animal kingdoms are
again listed in Charts II and III in tabular form along with the approximate number of species within a phyla, and some of the synonymous names or other taxonomic categories that might help in making
cross-relationships between different classification schemes. Further aid
in the placement of organisms within these listed phyla can be obtained by reference to the sources cited below.
Although it would be preferable to use only one classification system down to the species level for a treatise like the present one, this is
not yet practical. While there are some controversies concerning even
the major groups shown here, the differences in opinion become even
greater in the lower groups. For taxonomic classification systems of
taxa below the phyla level, the authors will cite their taxonomic source
when necessary. Because of possible misinterpretation if only common
names are used, the genus, and if known, the species names will be
given.
Reasons for the existence of so much controversy concerning not
only the group into which an organism should be placed, but the
taxonomic rank to which different groups should be elevated have been
frequently discussed (2-4). Although some of these difficulties are
XIX
plant or animal kingdom, except on an arbitrary and artificial basis.
Certain organisms, furthermore, are classified as both plants and animals; i.e., Euglena, Volvox, etc. For convenience only, the green
flagellates of the Protozoa and their colorless counterparts are best
placed in the Euglenophyta or Chlorophyta, leaving the more highly
specialized colorless flagellates in the Protozoa. Most of the interrelationships between these groups of microorganisms are quite indistinct,
indicated by the dashed lines, but it is felt that any grouping of the
algae and fungi in one group, the Thallophyta, is highly artificial, and
that they represent many separate stocks that have been evolving independently for a long time.
Such a phylogenetic chart can be used as a guide to examples of
parallel or convergent evolution occurring in these major evolutionary
lines. For example, any morphological or biochemical characteristic
found only in the Mammalia and Insecta is probably the result of an
independent origin in the two groups, while a characteristic found in
all the main Chordata and none of the phyla along the main line leading to the Arthropoda would presumably have originated once sometime after the separation of the two groups indicated by the fork. The
step-by-step loss of morphological and biochemical characteristics
along any one line is possible, and a simple structure or function may
be the result of reduction rather than a result of a primitive condition.
The major phyla or divisions in the plant and animal kingdoms are
again listed in Charts II and III in tabular form along with the approximate number of species within a phyla, and some of the synonymous names or other taxonomic categories that might help in making
cross-relationships between different classification schemes. Further aid
in the placement of organisms within these listed phyla can be obtained by reference to the sources cited below.
Although it would be preferable to use only one classification system down to the species level for a treatise like the present one, this is
not yet practical. While there are some controversies concerning even
the major groups shown here, the differences in opinion become even
greater in the lower groups. For taxonomic classification systems of
taxa below the phyla level, the authors will cite their taxonomic source
when necessary. Because of possible misinterpretation if only common
names are used, the genus, and if known, the species names will be
given.
Reasons for the existence of so much controversy concerning not
only the group into which an organism should be placed, but the
taxonomic rank to which different groups should be elevated have been
frequently discussed (2-4). Although some of these difficulties are