Chapter 13: Mollusks, Worms, Arthropods, Echinoderms

Spiders Because spiders can’t chew their
food, they release enzymes into their prey that
help digest it. The spider then sucks the predigested
liquid into its mouth.
Oxygen and carbon dioxide are exchanged
in book lungs, illustrated in Figure 19. Openings
on the abdomen allow these gases to move
into and out of the book lungs.
Book
lungs
Mites and Ticks Most mites are animal or plant parasites.
However, some are not parasites, like the mites that live
in the follicles of human eyelashes. Most mites are so small
that they look like tiny specs to the unaided eye. All ticks are
animal parasites. Ticks attach to their host’s skin and remove
blood from their hosts through specialized mouthparts.
Ticks often carry bacteria and viruses that cause disease in
humans and other animals. Diseases carried by ticks include
Lyme disease and Rocky Mountain spotted fever.
Centipedes and Millipedes
Two groups of arthropods—centipedes and millipedes—
have long bodies with many segments and many legs, antennae,
and simple eyes. They can be found in damp environments,
including in woodpiles, under vegetation, and in basements.
Centipedes and millipedes reproduce sexually. They make nests
for their eggs and stay with them until the eggs hatch.
Compare the centipede and millipede in Figure 20. How
many pairs of legs does the centipede have per segment? How
many pairs of legs does the millipede have per segment? Centipedes
hunt for their prey, which includes snails, slugs, and
worms. They have a pair of venomous claws that they use to inject
venom into their prey. Their pinches are painful to humans but
usually aren’t fatal. Millipedes feed on plants and decaying
material and often are found under the damp plant material.
Centipede
Heart
Air flowing
in through
spiracles
Blood flow
between folds
Figure 19 Air circulates
between the moist folds of the
book lungs bringing oxygen to
the blood.
Figure 20 Centipedes are predators—they
capture and eat other
animals. Millipedes eat plants or
decaying plant material.
Millipede
SECTION 3 Arthropods 375
(l)Bill Beatty/Animals Animals, (r)Patti Murray/Animals Animals