Geoscience Reference
In-Depth Information
mites (Acari), spiders (Araneae), harvestmen (Opiliones), false
scorpions (Pseudoscorpiones), whip scorpions (Uropygi), true
scorpions (Scorpiones)
Arachnida
millipedes (Diplopoda), centipedes (Chilopoda), symphylids
(Symphyla), Pauropoda
Myriapoda
I NSECTA
Apterygota
('primitive in-
sects'
springtails (Collembola), bristle-tails (Thysanura), Protura,
Diplura (Fig. 3)
about 13 orders of 'higher' insects with terrestrial representat-
ives in Britain
Pterygota
burrowing snakes and amphibians , true moles , marsupial mole
and mole-rats
V ERTEBRATA
S OIL MICRO-ARTHROPODS
Soil invertebrates span at least four orders of magnitude in size, from the smallest
protozoa about 0.02mm long to the largest earthworms which can reach 200mm in
this country and considerably more in the tropics. Attempts have been made to clas-
sify them into large, medium and small forms - the macro-, meso- and microfauna
- rather as soil pores have been divided into macro-, meso- and micropores ( chapter
1 ) . It is easy enough to place earthworms in the macrofauna, and soil protozoa, which
need a compound microscope to see them properly, in the microfauna. Other groups,
however, such as beetles and millipedes, span an uncomfortably wide range of sizes
from about 1 to 50mm, and are not so easy to categorize in this way.
The term micro-arthropod, however, is a convenient one to encompass several
unrelated groups of small arthropods whose largest members are less than about 5mm
in length. They include two major groups, mites and springtails, and a few minor
groups which often have no common name, such as the Protura and Pauropoda. The
ecology of these latter groups is little known while the mites and springtails have at-
tracted a great deal of attention so we focus here on these two major groups to con-
sider some of their fascinating adaptations to soil life.
MITES
Mites, Acari or Acarina, are the most prolific arthropods in most soils and also the
most numerous in species. As their common name suggests, they are very small, usu-
ally 0.25-0.5mm in length and rarely more than 2-3mm. Linnaeus, the father of mod-
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