1. Arthropods
Chapter 28

2. Animal Classification
Sponges
Cnidarians
Worms
Mollusks
Arthropods
Echinoderms
Invertebrates
Class Arachnida
Class Crustacea
Class Insecta
Arthropods
Animals
Fishes
Amphibians
Reptiles
Ectotherms
(cold-blooded)
Vertebrates
Birds
Mammals
Endotherms
(warm-blooded)

3. 28-1: Characteristics of Arthropods

4. Characteristics Arthropod comes from the Greek words
“arthron” – joint
“pod” – foot
Typical arthropods:
Segmented
Coelomate
Bilateral symmetry
Exoskeleton

5. Characteristics
Appendages – any structure (a leg or an antenna) that grows out of the body of an animal

6. Characteristics
Arthropods are the earliest known invertebrates to exhibit jointed appendages
Joints are advantageous because they allow more flexibility and powerful movements

7. Arthropod Exoskeletons Provide Protection
Exoskeleton is made of protein and
chitin (KI tun)
Chitin is also found in cell walls of fungi
The exoskeleton protects and supports internal tissues and provides places for attachment of muscles

8. Arthropod Exoskeletons Provide Protection
The weight of the exoskeleton limits the size of arthropods
The larger an arthropod is, the thicker and heavier its exoskeleton must be to support its larger muscles

9. Why Arthropods Must Molt
Exoskeletons cannot grow, so they must be shed periodically
Molting – shedding the old exoskeleton
Before an arthropod molts, a new, soft exoskeleton formed beneath the old one
Cicada

10. Segmentation in Arthropods
Arthropods do not have as many segments as segmented worms
In most groups, arthropods are consisted of three segments
Head
Thorax
Abdomen

11. Segmentation in Arthropods
Some arthropods have two sections
Cephalothorax – A fused head and thorax
Abdomen

12. Arthropods Have Efficient Gas Exchange
Three types of respiratory structures have evolved in arthropods:
1. Gills – Aquatic arthropods exchange oxygen and carbon dioxide through gills

13. Arthropods Have Efficient Gas Exchange
Land arthropods have either:
2. Tracheal tubes – branching networks of hollow air passages that carry air throughout the body

14. Arthropods Have Efficient Gas Exchange
3. Book lungs – air-filled chambers that contain leaf-like plates

15. Arthropods Have Acute Senses
Movement, sound, and chemicals can be detected with great sensitivity by antennae
Antennae are also used for sound and odor communication; can detect pheromones
Atlas moth

16. Arthropods Have Acute Senses
Pheromones – chemical odor signals given off by animals
Some pheromones are used as scent trails (example: the group-feeding behavior of ants)
Many pheromones are important in the mating behavior of arthropods

17. Arthropods Have Acute Senses
Most arthropods have one pair of large compound eyes and three to eight simple eyes
A simple eye is a visual structure with only one lens that is used for detecting light

18. Arthropods Have Acute Senses
A compound eye is a visual structure with many lenses
Compound eyes can detect the movements of prey, mates, or predators, and can also detect colors

19. Arthropods Have Acute Senses
Arthropods have hairlike structures used to detect movement
Ex. Fly and flyswatter

20. Arthropod Nervous Systems are Well Developed
The nervous system consists of a double ventral nerve cord, an anterior brain, and several ganglia
Ganglia act as control centers for the body sections in which they are located

21. Arthropods Have Other Complex Body Systems
Arthropods have open circulatory systems and complete digestive systems
Mouth, stomach, intestine, and anus

22. Arthropods Have Other Complex Body Systems
Mandibles – the mouthparts of most arthropod groups include one pair of jaws
The mandibles are adapted for holding, chewing, sucking, or biting

23. Arthropods Have Other Complex Body Systems
Malpighian tubules – used to excrete wastes into the intestine

24. Arthropods Reproduce Sexually
Some species (bees, ants, and wasps) exhibit parthenogenesis – a form of asexual reproduction in which a new individual develops from an unfertilized egg
In bees, drones are developed from unfertilized eggs

25. 28-2: Diversity of Arthropods
Diversity of All Animals
About 85% of all known animals are arthropods

26. Additional information

27. Arachnids
Spiders, scorpions, mites, and ticks belong to the class Arachnida
Spiders are the largest group of arachnids
An arachnid has a cephalothorax and an abdomen with six pairs of jointed appendages

28. Arachnids
Chelicerae [kuh-lis-er-uh] – the first pair of appendages located near the mouth (modified pinchers or fangs)
Pincers are used to hold food, and fangs inject prey with poison

29. Arachnids
Pedipalps – the second pair of appendages that is adapted for handling food and for sensing
In male spiders, pedipalps are used to carry sperm during reproduction
The four remaining appendages are adapted as legs

30. Arachnids
As silk is secreted, it is spun into thread by structures called spinnerets, located at the rear of the spider

31. Arachnids – Black Widow

32. Crustaceans
Crustaceans are the only arthropods that have two pairs of antennae for sensing
Some crustaceans have three body sections, and other have only two
Crustacean mandibles open and close from side to side
The blue crab has 3 body sections

33. Crustaceans
Class Crustacea include crabs, lobsters, shrimps, crayfishes, pill bugs, and barnacles
Most crustaceans are aquatic and exchange gases over gills

34. Crustaceans – Red Crab Mating

35. Crustaceans – Red Crab Offspring

36. Centipedes and Millipedes
Centipedes and millipedes have tracheal tubes for gas exchange
Centipedes are carnivorous and eat soil arthropods, snails, slugs, and worms
These arthropods can bite

37. Centipedes and Millipedes
A millipede eats mostly plants and dead material on damp forest floors
Millipedes do not bite, but they can spray foul-smelling fluids from stink glands

38. Insects Class Insecta is the largest group of arthropods
Insects have three body segments and six legs

39. Insects – Giant Asian Hornets (Invasive Species) vs
Insects – Giant Asian Hornets (Invasive Species) vs. European Honey Bees

40. Insects – Giant Asian Hornets (Invasive Species) vs
Insects – Giant Asian Hornets (Invasive Species) vs. Japanese Honey Bees

41. Insects – Botfly

42. Insect Reproduction Insects usually mate once during a lifetime
Some insects exhibit parthenogenesis
Most insects lay a large number of eggs, which increase the chances that some offspring will survive long enough to reproduce

43. Metamorphosis
Metamorphosis – the series of changes, controlled by chemical-substances in the animal
Two types of metamorphosis:
1. Complete metamorphosis consists of four stages:
Egg
Larva – the free-living, wormlike stage of an insect
Pupa – a period of reorganization in which the tissues and organs of the larva are broken down and replaced by adult tissues
Adult

45. Metamorphosis Examples: ants, beetles, flies, and wasps
Complete metamorphosis is an advantage for arthropods because larvae do not compete with adults for the same food

46. Metamorphosis With each molt, it begins to resemble the adult more
2. Incomplete metamorphosis – insects go through only three stages of development
Egg
Nymph – hatches from an egg, has the same general appearances the adult but is smaller
Adult
With each molt, it begins to resemble the adult more
Grasshoppers and cockroaches undergo incomplete metamorphosis

47. Picture of incomplete metamorphosis

48. Collecting Arthropods
1. Pitfall Traps
2. Flying Traps

49. Pitfall Trap
Cup
Water
Soap
Paper plate
Sticks
Labels

50. Flying Trap
Water bottles
Scissors
Twine or yarn
Labels