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