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Arthropods
Chapter 28
What is an Arthropod?
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Characteristics:
Invertebrate animals
with bilateral
symmetry
A coelom
Exoskeleton
Joint appendages
Appendages
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Are anything like
legs, antenna that
grows out of the body
Are adapted for
sensing, walking,
feeding & mating
Arthropods were 1st
to evolve jointed
appendages
Appendages
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Allows for more
powerful movements
Different uses
ex: spiders use
their 2nd pair of
appendages for
sensing & mating
Ex: scorpions
seize their prey
Purpose of exoskeleton
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Gives protection
Supports internal
tissue-gives muscles
place to attach
Some covers entire
body-some animals
held together by
hinges
Made of Chitin
Disadvantages of Exoskeleton
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Relatively heavy
structure (Jump &
Fly)
Cannot grow so they
shed periodicallymolting
Most molt 4-7 times
during their life
Most vulnerable to
predators
Steps Associated with Molting
1.
2.
3.
A new one develops beneath the old one
The muscles contract in the rear part of the
body, forcing blood forward causing this
part of the body to swell & split
The animal wiggles out
Spider Molting
http://www.youtube.com/watch?v=zXhdr0TpOwY
Body segments of Arthropods
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Segments have fused
into 1 – 3 body
sections
1. Head
2. Thorax
3. Abdomen
Body segments of Arthropods
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Other groups have 2
body segments
1. Fused head &
thorax called a
cephalothorax
2. abdomen
Movement
Generally quick, &
active
 Can crawl, run,
climb, dig, swim &
fly
Flies beat their wings
1000 times/sec
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3 types of Gas Exchange (Air)
1.
Gills
aquatic arthropods
(lobster, crayfish,
crab…) exchange gas
through gills
3 types of Gas Exchange (Air)
2. Tracheal Tubes
Most insects have
tracheal tubesbranching network of
hollow air passages
3 types of Gas Exchange (Air)
3.
Book lungs
Most spiders have
book lungs – air
filled chambers that
contain leaf-like
plates that look like
pages of a book
Acute Senses
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Movement, sound &
chemicals are
detected with an
antennae
Antennae also aid in
communication
Antenna
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Ants work together
because they
communicate with a
pheromone-which is a
chemical odor signal
given off by the
animal and detected
with the antenna
A Bugs Life…Wonderful Example
http://www.youtube.com/watch?v=jrW_TTxP1ow
Vision is important
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Most arthropods have 1
pair of large compound
eyes (visual structures
with many lens)
Or 3-8 simple eyes
(visual structure with 1
lens)
Total images make up
thousands of parts (dots
like a t.v. screen)
Nervous System
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Well-developed that
can process
information coming
in from the sense
organ
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Most excrete waste
through Malpighian
Tubes
Other complex body systems
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Mouth parts include a variety of jaws
called mandibles adapted for holding,
chewing, sucking or biting different foods
Other information
1. Have separate male &
female species
2. Reproduce sexually
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-fertilization
occurs internally in
land species
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-externally in
aquatic species
3. Blood is pumped by 1
or more hearts to an
open circulatory
system
4. Have complete
circulatory system, &
digestive system
Beneficial to Humans
1.
2.
3.
Pollinate many
flowering plants &
crop plants
Provide food, honey,
shellac, wax & silk
Provide alternative
chemical control of
insects
4. Research has
advanced in the fields
of genetics, evolution,
and biochemistry
-Crab shells make
artificial skin,
surgical sutures &
antifungal medicines
Problems for Humans
1.
2.
3.
Insects eat important
crops (bole weevil)
Spread plant and
animal disease
(malaria & yellow
fever)
Costly for us…
Crustaceans
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Crustaceans:
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Characteristics:
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Mostly are aquatic
Have mandibles for
crushing food
2 pairs of compound
eyes which are on
moveable stalks
5 pairs of walking
legs used to seize
prey & clean
appendages
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The first pair of walking legs are often modified into
strong claws for defense.
Members of Crustaceans
Shrimp
Crab
Barnacles
A Few Land Crustacean
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Pill Bug & Sow Bug,
two of the few land
crustaceans, must live
where there is
moisture, which aids
in gas exchange
Sow Bug
Pill Bug
Horseshoe Crab
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Horseshoe crabs are
considered to be
living fossils & have
remained relatively
unchanged since the
Triassic Period
They forage on sandy
or muddy ocean
bottoms for algae,
annelids, and
mollusks
Insects: class Insecta
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Insects have three body
segments and six legs
There are more species of
insects than all other
classes of animals
combined.
Only group of animal that
has never lost an
individual to extinction
Centipedes
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Centipedes are
carnivorous and eat
soil arthropods,
snails, slugs, and
worms
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The bites of some
centipedes are painful
to humans.
Millipedes
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A millipede eats mostly
plants and dead material
on damp forest floors.
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Millipedes do not bite,
but they can spray foulsmelling fluids from their
defensive stink glands.
Leaf Cutter Ants
http://www.youtube.com/watch?v=RH3KYBMpxOU
Other Members…
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Lice, Grasshoppers,
flies, butterflies, bees
& beetles….
Insect Reproduction
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Most insects lay a
large number of eggs,
which increase the
chances that some
offspring will survive
long enough to
reproduce.
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The insect embryo
develops and the eggs
hatch
Metamorphosis: change in body
shape and form
• This series of changes, controlled by
chemical-substances in the animal
• 2 types of metamorphosis
1. Complete Metamorphosis
2. Incomplete Metamorphosis
Complete Metamorphosis
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Complete metamorphosis consist of four stages
on their way to adulthood:
Egg  Larva  Pupa  Adult.
Incomplete Metamorphosis
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Incomplete metamorphosis consist of three
stages on their way to adulthood
Egg  Nymph  Adult
Arachnids
Spiders, Scorpions, Mites & Ticks
Arachnids
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30,000 species of
spiders – only 12
native to North
America
Cannot chew fooduse digestive enzyme
to liquefy food
Crab Spider
Ticks & Mites
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Differ from spiders
because they only
have one body
segment
scorpions
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Scorpions are easily
recognized by their
body segments &
enlarged pinchers
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They have a long tail
with a venomous stinger
at the tip.
Arachnids known for webs
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Silk is made from silk
glands & is spun into
thread by spinnerets
located at the rear of
the spider
Link for spider webs
http://www.i-is.com/users/robin/spiderweb.html
Spider spinning an insect
http://www.youtube.com/watch?v=_-A8Oe43tjg&NR=1
Venomous Spiders…
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Black Widow
web used in WWI for
cross-hairs in riffles
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Brown Recluse
Spiders
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1st pair of appendages
called chelicera
(located near mouth,
modified
pinchers/fangs) used
to hold food
2nd pair called
pedipalas handle food
& sensing
Banana Spider