2. Arthropods Chapter 36
Chapter 36

3. Phylum Arthropoda
Section 36.1

4. Arthropods
Examples: lobsters, crabs, spiders, millipedes, centipedes, insects
Arthropod means “jointed foot”
Appendages: body segments with jointed extensions
Used in feeding, moving, & mating

5. Characteristics: Exoskeleton Compound eye Open circulatory system
Protection, support, prevents desiccation
3 layers excreted by epidermis
Made of chitin
Compound eye
Optic nerves send impulse to the ventral nerve cord
Open circulatory system

6. Molting: Video Periodic shedding of the exoskeleton to allow growth
Few day process to develop hard exoskeleton – extremely vulnerable times!
Hormone, pressure, and enzyme induced
enzymes digest old exoskeleton while synthesizing new one
Video

8. Evolution: 545 million years ago
All from a common ancestor
Tagmata: fused segments that perform a specialized function of modern arthropods
5 subphlya

9. Classification: 5 Subphyla
Trilobita:
(trilobites)
Extinct!
Crustacea:
(shrimp, lobster, crayfish, pill bugs, barnacles)
Chelicerata:
(spiders, scorpions, ticks, horseshoe crab)
Myriapoda:
(centipedes, millipedes)
Hexapoda:
(insects, springtails)
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10. Subphylum Crustacea
Section 36.2

11. General Information: “Crusta” means shell Most are aquatic
Defining characteristic = 2 pairs of antennae
Exoskeleton:
Made up of chitin (protein) or CaCO3
Carapace has waxy coating
16 to 20 body segments that fuse to form tagmatas

12. General Information: Many have mandibles
jawlike mouthparts
Usually each segment has at least 1 pair of appendages
Open circulatory system
Many respire with gills (aquatic only)
Nauplius
Free swimming larvae

13. Crustacean Diversity Aquatic: Terrestrial: Isopods
Plankton – collection of small animals that drift near the surface of the water
Copepods (crustaceans) are a part of plankton
Water flea
Barnacles
Shrimp
Lobster
Crabs
Crayfish
Terrestrial: Isopods
Pill and sow bugs
Lose water quickly

14. Crayfish
Decapods – “ten feet,” five pairs of legs

15. THIS IS WHAT WE
WILL BE DISSECTING
– WEAR CORRECT SHOES!
Video

16. External Structure Two major sections: Cephalothorax: two tagmata
Head – 5 segments
Thorax – 8 segments posterior to head
Carapace – dorsal exoskeleton
Abdomen:
7 segments
Telson – 7th segment,
flat paddle at posterior

17. Appendages: Antennules – touch, taste, equilibrium
Antennae – touch, taste
Mandible – chewing
Maxilla – manipulate food, draw water over gills
Maxilliped – touch, taste, manipulate food

18. Cheliped (claws) – capture food, defense
Walking legs – locomotion over solid surfaces
Swimmeret – create water currents, transfer sperm (male), carry eggs and young (female)
Uropod – propulsion during tailflips

20. Digestion:
Digestive System: mouth  esophagus  stomach  enzymes secreted by digestive gland  intestine & digestive gland  anus

21. Respiration: Respiratory System: gills
Base of each walking leg under carapace
Diffusion of gases

22. Excretion: Excretory System: green glands Acts like a kidney
Eliminate excess water due to hypotonic environment

23. Circulation: Circulatory System: open system baths organs in hemolymph
Pumping organ: heart (dorsal)

24. Neural Control: Brain = pair of ganglia above esophagus
Ventral nerve cord
Sensory hairs on exoskeleton
2,000 light sensitive units on each eye
Statocyte at base of antennae for balance

25. Reproduction: Video Sexual: mate in fall
Male’s first 2 hollow legs transfer sperm
Female holds sperm until eggs laid, then fertilize; mated previous fall
Eggs laid in spring (100)
carried by female on swimmerets 6-8 weeks; “berried”
regenerate missing parts
Video

26. Female
Male

27. Subphyla Chelicerata & Mryiapoda
Section 36.3

28. Subphyla Chelicerata
Examples: spiders, scorpions, mites, horseshoe crab
Typically 6 pair of appendages
1st pair = chelicerae (modified pincers or fangs)
Video

29. Class Arachnida:
Arachnids include spiders, scorpions, mites, and ticks
Cephalothorax has 6 pairs of jointed appendages:
one pair of chelicerae (pincers or fangs)
one pair of pedipalps (aid in holding food & chewing)
Four pairs of walking legs

30. Anatomy of a spider: Chelicerae = modified fangs 8 simple eyes
Spinnerets = produce silk

31. Respiratory System Book lungs = paired sacs with parallel folds
Tracheae = system of tubes carrying air directly to tissues
Air in through spiracles in exoskeleton
Some have one or the other
Some have both!

32. Excretory System
Malpighian tubules = hollow projections of digestive tract
Collect body fluids & waste
Waste leaves as feces
Helps conserve water in spider
Coxal glands = organ that removes wastes & discharges through openings at base of legs OR

33. Feeding: Video Use webs to capture prey
Inject venom to paralyze animal
Two harmful spiders to humans = black widow & brown recluse

34. Reproduction: Video Transfer of sperm to tip of pedipalps
Sperm place into seminal receptacles on female
Male flees to avoid being eaten
Eggs fertilized as passed out of female
Fertilized eggs into silken case
Female carries eggs or attaches to plant
Young spiders hatch in two weeks
Video

35. Scorpions Large, pincerlike pedipalps in forward position
Large stinger on last segment of abdomen curled over body
Hunt insects & spiders at night
Inject venom into prey
video

36. Ticks Many parasitic Pierce host’s skin, feed on blood
Transmits bacteria & microorganisms
Lyme disease
Rocky Mountain spotted fever

37. Subphylum Myriapoda Myriapods = “many feet”
Examples: millipedes & centipedes
First animals on land
Segmented bodies
Live in damp environments

38. Class Diplopoda Examples: millipedes Round bodies Appendages:
Two pair of legs on each segment
Short antennae
Two groups of simple eyes
When threatened: coil up & secrete noxious fluid with cyanide
Food source: decaying plant material

39. Class Chilopoda Example: Centipedes Flat bodies Appendages:
Long, jointed legs
Poison claws
Long antennae
Two clusters of simple eyes
Prey = earthworms, insects, NOT humans!
Video