Chapter 28
PHYLUM ARTHROPODA: KEY
1. What are the four subphyla of arthropods? Give examples of
each.
Trilobita – now extinct, predominated in Paleozoic seas, 544-250
million years ago
Chelicerata – spiders, ticks, mites, scorpions, horseshoe crabs
Crustacea – crabs, shrimp, lobsters, barnacles, oysters
Uniramia – centipedes, millipedes, insects (bees, moths, flies,
beetles, etc…..)
2. Why are there so many different kinds of arthropods?
They have been around on Earth for over 600 million years 
evolved in aquatic and terrestrial environments
3. List some unifying characteristics of this phylum.
a) Exoskeleton - All members of this phylum have an external
skeleton made of chitin. It provides protection.
b) Metamerism - This means that the body of the Arthropods is
composed of numerous segments.
c) Jointed Appendages - Arthropods have joint appendages, which
are modified into specialized organs for walking, eating, and grasping
purposes.
d) They have a dorsal heart.
e) Ventral Nervous System
- They have a ventral nerve cord with ganglia(swellings) in each
segment.
f) Open Circulatory System
g) Sexual Reproduction - Sexual reproduction or the uniting of
female and male gametes is the most common mode of reproduction
in Arthropods. But, there are some parthenogenic
insects. Parthenogenesis means that the females produce female
offspring without mating.
4. List three benefits associated with the arthropod exoskeleton.
-protection from physical damage and predators
-waterproof exoskeleton prevents dessication in extremely dry
environments
-helps support body/movement
5. What are the disadvantages of the exoskeleton?
Exoskeleton is like a suit of armour.
-it cannot grow with the animal
-movement can only occur at joints
6. Explain how the jointed appendages in arthropods differ from
those seen in primitive arthropods.
In primitive arthropods, every body segment had a single pair of
appendages, but in modern arthropods some body segments are fused
and appendages lost. Appendages have adapted to enable different
arthropods to survive in their environments. Appendages include
antennae, claws, walking legs, wings, flippers, etc…
7. Describe the feeding behaviours of arthropods.
Every mode of feeding is seen in arthropods: herbivores, carnivores,
detritus feeders, parasites, filter feeders.
8. What are the FOUR basic types of respiratory structures
found in arthropods.
Gills – row of feathers located just under cover of exoskeleton
-in aquatic arthropods (crustaceans)
Book Gills – found in horseshoe crabs -located under the body
Book Lungs – in arachnids – located in a sac within the body which
opens to outside via the spiracle
Tracheal
Tubes – in
most
terrestrial
arthropods (i.e. insects, some spiders, millipedes)
-tracheal tubes lead from spiracles along body to tissues deep in
arthropod’s body
-body muscle movements cause tracheae to shrink and expand,
pumping air in and out of spiracles
9. Construct a chart describing each of the respiratory
structures in #8, including the types of organisms they are
found in.
10. Describe the flow of blood in the circulatory system of
arthropods.
Arthropods have a well-developed heart which pumps blood into
arteries which branch into smaller vessels that enter the tissues 
once oxygen is dropped off, blood moves into spaces called sinuses
and eventually into large cavities surrounding the heart  blood reenters heart through small openings
11. Metabolic wastes are excreted in different ways in both
terrestrial and aquatic arthropods. Explain.
Terrestrial arthropods use malpighian tubules which are bathed in
blood inside the body sinuses  tubules remove waste from blood,
concentrate them, and add them to undigested food leaving through
anus. Some terrestrial arthropods have small excretory glands at
base of their legs instead.
In aquatic arthropods, wastes can diffuse out of body at unarmored
places like the gills. Some like lobsters accumulate nitrogencontaining wastes in glands which are emptied periodically.
12. Describe the layout of the nervous system in arthropods.
The nervous system is annelid-like, with a brain (a pair of ganglia) in
the head. A pair of nerves surrounds the esophagus and connects
the brain to a ventral nerve cord that has ganglia in the body
segments. These ganglia serve as local command centers for the
segments they are in.
13. What are compound eyes?
A compound eye has a meshlike appearance
because it consists of hundreds or thousands
of tiny lens-capped optical units called
ommatidia. Each ommatidium has its own
cornea, lens, and photoreceptor cells for
distinguishing brightness and color.
-wide field of view and excellent at detecting
motion
14. Where are chemical receptors for taste and smell found in
crustaceans and insects?
On the mouthparts, antennae, and legs.
15. Why are crustaceans and insects able to move away rapidly,
especially when one is trying to catch them?
As well as their excellent vision, they have sensory hairs that detect
movement in air or water.
16. How is the sense of hearing in insects?
Many have well-developed ears that hear sounds above the human
range.
17. How do different arthropods protect themselves against
predators?
-well-developed sense organs help detect and escape predators
-tough exoskeleton
-venomous stings (bees, scorpions, some ants)
-venomous bites (spiders, centipedes)
-claws (lobsters, crabs)
-chemicals (many insects, millipedes)
-dropping body parts to distract predator (crab)
-camouflage
-mimicry: imitating the warning coloration of poisonous or dangerous
species
18. Briefly describe reproduction in arthropods.
Most common mode is sexual reproduction. In spiders and some
crustaceans, female picks up packets of sperm left behind by male
spiders. In most insects and crustaceans, male uses a special
reproductive organ to deposit sperm inside the female.
19. Why do arthropods molt?
To grow, they need to shed their exoskeleton.
20. Describe the process of molting.
Process is controlled by hormones (molting hormone). Begins when
epidermis digests inner part of exoskeleton and absorbs the chitin to
recycle chemicals. A new exoskeleton is secreted inside old one and
arthropod pulls out of old exoskeleton. The new soft exoskeleton
expands to cover the larger animal. The exoskeleton slowly hardens
over time.
21. What is the difference between metamorphosis and incomplete
metamorphosis? In which organisms does each occur?
Complete Metamorphosis
Incomplete Metamorphosis
Incomplete Metamorphosis
About 12% of all insects go through incomplete metamorphosis.
Incomplete metamorphosis has 3 stages.


Egg - A female insect lays eggs. These eggs are often covered
by an egg case which protects the eggs and holds them
together.
Nymph - The eggs hatch into nymphs. Nymphs looks like small
adults, but usually don't have wings. Insect nymphs eat the
same food that the adult insect eats. Nymphs shed or molt
their exoskeletons (outer casings made up of a hard substance
called chitin) and replace them with larger ones several times as
they grow. Most nymphs molt 4-8 times.

Adult - The insects stop molting when they reach their adult
size. By this time, they have also grown wings.
Occurs in grasshoppers, aphids, crickets, cockroaches,
dragonflies, mites.
http://www.morning-earth.org/Graphic-E/Transf-Metam.html
Complete Metamorphosis
About 88% of all insects go through complete metamorphosis.
Complete metamorphosis has 4 stages:




Egg - A female insects lays eggs.
Larva - Larvae hatch from the eggs. They do not look like
adult insects. They usually have a worm-like shape.
Caterpillars, maggots, and grubs are all just the larval stages
of insects. Larvae molt their skin several times and they grow
slightly larger.
Pupa - Larvae make cocoons around themselves. Larvae don't
eat while they're inside their cocoons. Their bodies develop into
an adult shape with wings, legs, internal organs, etc. This
change takes anywhere from 4 days to many months.
Adult - Inside the cocoon, the larvae change into adults. After
a period of time, the adult breaks out of the cocoon.
Occurs in insects like butterflies, flies, bees, wasps, ants, moths,
and beetles.