Arthropods
Chapter 28
Arthropods include:
• Insects, Arachnids, Crustaceans, Centipedes
Common characteristics
of all arthropods:
1. Invertebrates-no backbone
2. Bilateral symmetry- divide
into 2 equal sides at one
point
3. Coelom- cavity around
internal organs
4. Exoskeleton-outside body
skeleton
5. Jointed appendagesstructures growing out of
body have joints
6. Open circulatory system –
blood pools in spaces (not
vessels)
Common characteristics cont…
7. Complete digestive system -mouth,
intestines, stomach, anus
8. Mandibles-a variety of jaws/
Functions: hold, chew, suck, and bite
Appendages
• Used for 1. locomotion, 2. sensing, 3.
feeding, 4. mating
Exoskeleton
• Hard thick covering
made of protein & chitin
• May be solid all over
body or may be in
segments
Functions
1. Protect
2. Support internal
tissues
3. A place of attachment
for muscles, prevents
4. Water loss
Exoskeleton growth
• Can’t grow as the body
grows
• They must shed the old
skeleton & grow a new
one/process called
molting
• The new skeleton will
grow underneath &
eventually pop off the old
one
• Most arthropods molt 4-7
times in life
Most arthropods have 3 segments
to their body
These include:
-The head
-The thorax (chest area)
-The abdomen
How do arthropods breathe
(respire)?
1. Aquatic arthropods-use gills ex. Crayfish
Breathing cont…
2. Most insects use tracheal tubes
-branching networks of hollow air passages
that carry air through body.
-Muscles pump air through the tubes to
openings called spiracles.
Ex. grasshopper
Breathing cont…
3. Arachnids use
book lungs
-these air
chambers are
stacked like
books
Ex. Spider
Arthropods have acute (very good)
senses
1. Quick movement Ex. Fly
2. Antennae-use to detect and
communicate
3. Pheromones-chemicals
used to signal Ex. Ants
4. Acute vision (simple and
compound eyes)
-detect motion very well
-can see in almost all directions
except directly behind.
Ex. This is why it is hard to
hit a fly!
Reproduction in Arthropods
• Most have 1 type of sex organ on each
(male or female)
• A few are hermaphrodites (male &
female organs)
Types of fertilization
-If it lives on land-fertilization is internal
-If it lives in water-fertilization is external in
water
Arthropod classification:
• Kingdom: Animalia
• Phylum: Arthropoda
• Classes: 4 classes
4 classes of
arthropods
1. Arachnids-spiders, scorpions, mites, ticks
2. Crustaceans-all are aquatic-lobster,
shrimp, crayfish
3. Centipedes & millipedes- they differ on
the number of legs on each section & the
type of food they eat
• Includes millions
of species
(largest group)
• Mate only around
1 time in lifetime
• Eggs are fertilized
internally and
shells form around
the eggs
• Female lays the
eggs after they are
fertilized
• The # of eggs laid
is enormous
– Purpose: to
increase chance of
survival
Class Insecta:
Insect cartoon
Changes insects undergo after
hatching:
Metamorphosis-series of
changes controlled by
chemical substances
2 Types of Metamorphosis:
1. Complete metamorphosishas 4 stages
(ex. Butterfly)
4 stages:
a. Egg
b. larva-free living worm-like
stage (caterpillar)
c. pupa-larva tissue broken
down and replaced in a
case-cocoon
d. adult
Complete metamorphosis:
2. Incomplete
metamorphosis has 3 stages
(Ex. Grasshopper)
3 stages:
a. egg
b. nymph-smaller
version of adult
(looks like adult but
lacks appendages
like wings and
cannot reproduce
c. adult
Know Insect Structures!
• P. 752 Draw and
label the
grasshopper
• Write the functions
under each labeled
part
• Leave in notebook
to study for test
• Study drawing,
functions and notes
for test