Chapter 17: Invertebrate Animals

Circulatory System Insects have an open circulatory system.
Oxygen is not transported by blood in the system, but food
and waste materials are. Oxygen is brought directly to the
insect’s tissues through small branching tubes. These tubes connect
to openings called spiracles (SPIHR ih kulz) located along
the sides of the thorax and abdomen.
Metamorphosis The young of many insects don’t look anything
like the adults. This is because many insects completely
change their body form as they mature. This change in body
form is called metamorphosis (met uh MOR fuh sus). The two
kinds of insect metamorphosis, complete and incomplete, are
shown in Figure 18.
Butterflies, ants, bees, and beetles are examples of insects
that undergo complete metamorphosis. Complete metamorphosis
has four stages—egg, larva, pupa (PYEW puh), and
adult. Notice how different each stage is from the others. Some
insects, such as grasshoppers, cockroaches, termites, aphids, and
dragonflies, undergo incomplete metamorphosis. They have
only three stages—egg, nymph, and adult. A nymph looks similar
to its parents, only smaller. A nymph molts as it grows until
it reaches the adult stage. All the arthropods shown in Figure 19
on the next two pages molt many times during their life.
Topic: Butterflies
Visit red.msscience.com for
Web links to information about
butterflies.
Activity What are some of the
characteristics that are used to
identify butterflies Make a diagram
of the life cycle of a butterfly.
Figure 18 Insect metamorphosis occurs in two ways.
State the name given a moth larva.
Adult
Egg
Eggs
Nymph
Molt
Nymph
Molt
Pupa
Larva
Adult
Bees and many other insects
undergo the four stages of complete
metamorphosis.
Insects like the grasshopper
undergo incomplete
metamorphosis.
SECTION 4 Arthropods and Echinoderms 513