1. Arthropods

2. What are ARTHROPODS?
• Coelomate
• Segmented
• Bilateral Symmetry
• Exoskeleton – made of protein and chitin
• Jointed appendages – any structure (leg or
antennae) that grows out of the body

3. What are Arthropods?
• earliest invertebrates to exhibit jointed
appendages
– Jointed appendages are an advantage
because they allow more flexibility for
animals with hard, rigid exoskeletons
– Joints allow powerful movements and allow
appendages to be used in many ways

4. What are Arthropods?
Appendages
Jointed Appendages

5. Exoskeletons Provide Protection
• made up of protein and CHITIN
• can be a continuous
covering over most
of body OR
made of plates
that are held Continuous
together by hinges
Hinged

6. Exoskeleton Advantages
• Protects, supports internal tissues
• Provides place for muscle attachment
• Aquatic arthropods have exoskeleton
reinforced with calcium carbonate

7. Exoskeleton Disadvantages
• Heavy
– the larger the animal, the thicker and
heavier the exoskeleton
• Exoskeletons don’t grow
– animals must molt when they get too large
for exoskeleton

8. Molting
• Animal contracts muscles and takes in
air or water
• Body swells and causes exoskeleton to
split open, usually along the back
• Most arthropods
will molt 4-7 times
before becoming
an adult.

9. Before the new exoskeleton
hardens...
• increased circulation to all parts of the
body cause the animal to puff up and
new exoskeleton hardens leaving some
“growing room”
• animal can’t protect itself, can’t move

10. Question 1
Which of the following organisms would be
most likely to have an exoskeleton reinforced
with calcium carbonate?
B. Spider
C. Beetle
Correct!
D. Crab
E. Dragonfly

11. Question 2
• Exoskeletons are heavy. Why can aquatic
arthropods grow so much larger than
terrestrial arthropods?
The buoyancy of the water helps support
the weight of the exoskeleton

12. Question 3
• What is one advantage and one
disadvantage of flying arthropods having
a thinner, lighter weight exoskeleton?
Disadvantage: less protection
Advantage: greater freedom to fly and
jump

13. Question 4
• What is one advantage and one
disadvantage of having a cephalothorax?
Disadvantage: less flexibility, mobility
Advantage: more protection

14. Segmentation
• 3 segments
– abdomen
– thorax
– head

15. Segmentation
• Sometimes these segments can be fused
together
– some have head and fused thorax and
abdomen
– some have abdomen
and fused head and
thorax (cephalothorax)

16. Respiration
• Efficient respiratory systems to meet
large O2 demands
• Large O2 demand needed to sustain high
metabolism for fast movements
• 3 types of respiratory structures
– gills (aquatic arthropods)
– tracheal tubes (terrestrial arthropods)
– book lungs (terrestrial arthropods)

17. Respiration
• Gills
– water moves over gills
– O2 from water diffuses
into gills and into
bloodstream
– CO2 from body diffuses out through gills
into surrounding water

18. Respiration
• Tracheal tubes
– branching network of hollow air passages
that take air throughout the body
Muscle
movement
brings air
in/out through
SPIRACLES
(openings in
abdomen and
thorax)

19. Respiration
• Book lungs
– spiders and relatives
– air filled chambers with leaf-like plates
– stacked plates
are arranged
like pages
of a book

20. Antennae
• Acute sensing by antennae
– stalk like structure that can detect changes
in the environment
• movement
• sound
• chemicals
Used for sound and odor communication

21. Eyes
• Compound Eyes
– visual structure with
many lenses
• Simple Eyes
– visual structure with one lens for detecting
light
one pair of compound eyes and 3-8 simple
eyes

22. Nervous System
• Double ventral nerve cord
• Anterior brain
• Several fused ganglia that control the
body section they are located in

23. Circulatory System
• Open circulatory system
– blood flows away from the heart in vessels
– blood flows out of vessels into tissues
– blood returns to the heart through open
spaces

24. Digestive System
• Complete digestive system with mouth,
intestine, and anus
• Mouth has 1 pair of jaws called
MANDIBLES
– adapted for holding, chewing, sucking, or
biting

25. Reproduction – Sexual and
Asexual
• Sexual reproduction
– separate sexes
– internal fertilization for terrestrial species
– external fertilization for aquatic species

26. Reproduction – Sexual and
Asexual
• Asexual reproduction
– PARTHENOGENISIS
• a new individual develops from an
unfertilized egg
• seen with ants, aphids and bees

27. Arachnids
• spiders (largest group), ticks, mites, and
scorpions
• 2 body regions: cephalothorax and
abdomen
• 6 pairs of jointed appendages – 12 total
appendages!

28. Arachnids
• 1st pair - chelicerae, are near the mouth
chelicerae
• modified into pincers (hold food) or fangs
(inject poison)

29. Arachnids
• 2nd pair – pedipalps, for handling food
and sensing
pedipalps

30. Arachnids
• Silk, for webs, is secreted by silk glands
in the abdomen
• as it is secreted, it is spun into thread by
SPINNERETTES
• spiders are predatory and feed almost
exclusively on other animals

31. Arachnids
• Ticks and mites have only 1 body section
• Head, thorax and abdomen are completely
fused
• Ticks feed on blood of other animals

32. Arachnids
• Mites feed on fungi, plants, and animals
• small – not usually visible
• can transmit diseases
Dust mites

33. Arachnids
• Scorpions have many abdominal body
segments
• Enlarged pincers
• Long tail with
venomous stinger
at the tip

34. Crustaceans
• crabs, lobster, shrimp, crayfish,
barnacles
• Only arthropods with 2 pairs of antennae
• mandibles – move
from side to side
• 2 compound
eyes

35. Crustaceans
• 5 pairs of walking legs
• 1st pair are claws for defense
claw legs

36. Crustaceans
• Most are aquatic and use gills
• pill bugs (roly-polies) live on land, but
must have moisture to aid in gas
exchange
Yes! This is a
crustacean!

37. Centipedes and Millipedes
• Centipedes are carnivorous – eat soil
arthropods, snails, slugs,
and worms
• Bites can be painful
• Millipedes – eats plants and dead
material on damp forest floors
• Does not bite, but does
spray foul-smelling fluid

38. Horseshoe Crabs
• Class Merostomata
• “Living Fossils”- unchanged for 220
million years (Triassic period)
• Extensive exoskeleton
• Live in deep coastal waters
• forage bottoms for algae,
annelids and molluscs

39. Insecta
• Flies, grasshoppers, lice, butterflies,
beetles
• 3 body segments
• 6 legs
• Very diverse - more insects than all other
classes of animals combined

40. Insecta
• mate once in lifetime
• internal fertilization
• some exhibit
parthenogenesis
• large number of eggs
to increase survival rate

41. Insecta
• insect embryos
develop inside
Molt
eggs, eggs
Eggs
Nymph
hatch
• some look like
Nymph miniature
Molt adults
Adult – will molt
several times
until adult size

42. Insecta
• INCOMPLETE METAMORPHOSIS
– 3 stages: egg, nymph, adult
• Nymphs can’t
reproduce
• Nymph
gradually
becomes an adult

43. Insecta
• Some undergo
COMPLETE Egg
METAMORPHOSI Adult
S
– 4 stages: egg, larva,
pupa, adult
• Metamorphosis is Larva
controlled by Pupa
chemical substances
in the insect

44. Insecta
• Incomplete metamorphosis:
grasshoppers and cockroaches
• Complete metamorphosis: ants,
beetles, flies, wasps

45. Origins of Arthropods
• Successful because of
– varied life styles
– high reproductive output
– structural adaptations
– hard exoskeletons
– jointed appendages

46. Origins of Arthropods
• Hard exoskeletons fossilize – a lot is
known about evolutionary history
• Evolved from ANNELIDS (segmented
worms)
• Arthropods have more complex
segments, more developed nervous
systems
• circular muscles in annelids do not exist
in arthropods

47. Question 5
Spiders are: Predators!
b. predators
c. scavengers
d. decomposers
e. parasites

48. Question 6
Having 2 pairs of antennae distinguish
_________ from other arthropods.
b. centipedes
Crustaceans!
c. millipedes
d. crustaceans
e. horseshoe crabs

49. Question 7
• Why are horseshoe crabs called “living
fossils?”
They
remain
unchanged
after 220
million
years!