Biology Reference
In-Depth Information
Table 12.1: Two Recent Higher Classifications of the Phylum Arthropoda Illustrate Changing
Views of the Evolutionary Relationships of the Arthropoda.
Daly et al. 1998
Whitfield and Purcell 2013
Phylum Arthropoda
Subphylum Trilobita
Subphylum Chelicerata
Class Merostomata
Class Pycnogonida
Class Arachnida
Subphylum Crustacea
Subphylum Labiata
Superclass Myriapoda
Class Diplopoda
Class Chilopoda
Class Pauropoda
Class Symphyla
Superclass Hexapoda
Class Parainsecta
(Protura and Collembola)
Class Entognatha
Class Insecta
Phylum Arthropoda
Subphylum Trilobita
Subphylum Chelicerata
Class Merostomata
Class Pycnogonida
Class Arachnida
Subphylum Crustacea
Subphylum Myriapoda
Class Diplopoda
Class Chilopoda
Class Pauropoda
Class Symphyla
Subphylum Hexapoda
Informal group Entognatha
Order Protura
Order Collembola
Order Diplura
Class Insecta
There is a broad overlap in the use of the terms
systematics
and taxonomy.
Mayr and Ashlock (1991)
define systematics as “the scientific study of the kinds
and diversity of organisms and of any and all relationships among them” or
the “science of the diversity of organisms” and
taxonomy
as “the theory and
practice of classifying organisms.” Taxonomy can be divided into descriptive tax-
onomy and identification (
Post et al. 1992
). Systematics deals with populations,
species, and higher taxa. It is concerned also with variation within taxa. Thus,
DNA analysis is particularly suitable for systematics studies because it is the most
direct analysis of the genetic material possible and is unlikely to show life stage
or environmentally induced variability.
During the 19th century, after Darwin's theory of evolution was proposed and
numerous new organisms were found, more-extensive nomenclature rules were
developed to accommodate the growing numbers of plant, animal and micro-
bial species. So far, an estimated 1.4 million species have been identified, but
these species may represent only 10% or so of the total species thought to live
on this planet.
Mora et al. (2011)
recently calculated that
≈
8.7 million eukaryotic
species exist globally. (The number of unknown microbial species may exceed
this number, and many may be important in the biology of arthropods.) Big
surprises still occur, even with the relatively well-known insects. A new order
