F-519930 
Figure 8.—Cross section of a piece of timber riddled 
with tunnels made by a molluscan shipworm of the 
genus Bankia. 
Phylum Arthropoda 
Insects belong to the phylum Arthropoda, one of the major groups of the animal 
kingdom. In the hierarchy of animal phyla it stands near the top, far removed from 
the simplest, one-celled organisms in the phylum Protozoa. The phylum also 
contains many other well-known forms such as crawfish, shrimp, millipedes, 
centipedes, spiders, and mites. Members of the phylum are distinguished by a body 
that is composed of a series of more or less similar rings or segments joined 
together, some of which bear jointed legs. In certain forms, the segmentations of 
the body may be obscure and not evident from cursory examination. In most 
instances this is due to a secondary modification of form, a result of adaptation to 
special modes of life (230). 
Insects constitute the most abundant and important group of arthropods, but 
many other members of the phylum are also common and often important. Many of 
the latter are harmful, either to trees and other vegetation or to wildlife and humans. 
Many are so small they are seldom seen, although enormously abundant; other, 
larger ones, are easily seen. Some of the latter are also many-legged and wormlike 
and bear little or no resemblance to insects; others are often mistakenly identified as 
insects. The arthropods discussed here belong to the classes Insecta (insects), 
Crustacea (crawfish, shrimp, crabs), Diplopoda (millipedes), Chilopoda (cen- 
tipedes), and Arachnida (spiders, mites, scorpions). 
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