Geoscience Reference
In-Depth Information
F
IG. 22
A fungal feeding uropodid mite (Mesostigmata). (National Museum of Wales.)
One subdivision, the Uropodina, are fungal and faecal feeders and are commonly
associated with ants' nests. They are often circular or oval in outline, with short legs
that fold away into grooves under the body (
Fig. 22
). When not moving, they look
like tiny discs from above with little to suggest that they are animate.
The Prostigmata are a heterogeneous assemblage of usually very small and often
soft-bodied mites. They are easily damaged by collecting methods that depend on
washing soils over a sieve, and often succumb to desiccation before they can escape
from samples subjected to heat. The only members of this order that are likely to be
seen without a microscope are the plump, scarlet mites, up to 4mm in length, of the
family Trombidiidae. They live under stones or in crevices and prey on smaller arth-
ropods.
COLLEMBOLA
Like the Acarina, the Collembola are one of the more ancient groups of arthropods,
forming an offshoot from the stock linking millipedes with true insects. They or
closely similar forms have been found as fossils in lower Devonian deposits around
400 million years ago, and some 100 million years before winged insects, such as
dragonflies, appeared. Their unique and universal feature is the possession of a vent-
ral tube on the first body segment behind the three pairs of legs. The name of the
group, indeed, derives from this feature (from the Greek words for glue-peg) before
