Islands; the troops, in crawling over the ground, came in contact with the glandular
fluids of these pests. Certain species of miIIipedes squirt their irritating fluids a distance
of several inches.
b. The members of this class are characterized by their long cylindrical bodies of
many segments with two pairs of legs and two spiracles for each of the body segments
(see figure 1-5). Some are brightly colored whereas others are black.
c. MiIIipedes prefer a dark, moist, terrestrial habitat such as is found under
rotting logs, leaves, or beneath stones. On certain of the tropical Pacific Islands,
miIIipedes have been observed crawling on low-lying bushes.
Section V. CLASS CRUSTACEA
1-15. GENERAL
Crustacea is a class containing a large number of species, most of which are
marine. The oceans are teeming with these animals which are said to occur at all
depths wherever animals Iive. Medical significance of the group is minor because
relatively few species cause injury to humans; the few species that do affect people
serve as intermediate hosts of human parasites. Humans become infected by drinking
water that has not been properly treated and which contains parasitized crustaceans.
Eating fresh-water crustaceans (crayfish and crabs, for example) that are raw or
insufficiently cooked may also produce an infection in the consumer.
1-16. RECOGNITION, CHARACTERISTICS, AND BIOLOGY
Crustaceans have a compact, rigid anterior body region and usually have a
visible segmented posterior region (see figure 1-6). Two pairs of antennae occur
anteriorly and three pairs of segmented appendages comprise the mouthparts. All body
segments may bear a pair of jointed appendages. Some species add segments as they
grow, and they may have 70 or more pairs of legs. All have closed respiratory systems
with gills. For examples of different kinds of crustaceans, see figure 1-6 and figure 2-2,
A Standard Identification Key to Common Classes and Orders of Arthropods of Public
Health Importance.
MD0170
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