Chapter 30

1. Chapter 30 Arthropods

2. Section 1 Features of Arthropods

3. Jointed Appendages • Phylum Arthropoda = joint foot • Appendage • Structure that extends from the arthropod’s body wall • Arthropod joints are able to bend • Legs, antennae and mouth parts • Like annelids, arthropods have a segmented body • Well-preserved fossil specimens

4. Arthropod Diversity • Total # of arthropod species is more than all other animal species combined. • Thought to be more than 5,000,000 species • Range in size from 1mm – 12 ft. • Arthropods divided into 2 groups: • Jaws • Fangs or pinchers

5. Arthropod Body Plan • All arthropods share numerous internal and external features • Not all arthropods share all of the same features below: • Jointed appendages • Segmentation • Distinct head w/ compound eyes • Exoskeleton • Respiration by gills, tracheae, or book lungs • Open circulatory system • Excretion through Malpighian tubules • Wings

6. Segmentation • Often exists during the larval stage • Butterfly • Segments usually fuse to form 3 body regions: • Head • Thorax • Mid-body region • Abdomen • The head may fuse with the thorax to form the cephalothroax

7. Compound Eye • Composed of multiple visual units • Each unit contains: • Lens and retina • Allow them to sense motion very quickly • Some arthropods also contain a single-lens eye that can only distinguish light from dark • Horizon detectors

8. Exoskeleton • External skeleton (shell) composed of chitin • Thin and flexible where joints are located • Chitin is a tough material, but can be brittle • As arthropods grow their exoskeletons become thicker to withstand the pull of larger muscles

9. Molting • Periodic shedding of the exoskeleton • Also called ecdysis • Allows arthropod to grow and develop • Triggered by hormone release • New exoskeleton hardens with a few hours to a few days

10. Respiration • Terrestrial arthropods • Utilize tracheae • Network of fine tubes • Air enters body through spiracles which passes it on to tracheae • Valves of spiracles allow air in and help prevent water loss • Key adaptation to live on land

11. Excretion • Arthropod excretion conserves water and eliminates metabolic waste • Malpighian tubules • Finger-like extensions from the arthropod’s gut that are bathed in blood • Process of excretion: • Water and other particles move through the tubules and into the gut • These particles are reabsorbed into body tissues • Waste remains in the gut until expelled from the body

12. Section 2 Spiders and Other Arachnids

13. Arachnid Modifications • Spiders, Scorpions, Ticks, Mites, Daddy longlegs • Generally do more good than harm • Chelicerae • Mouthparts modified into pinchers or fangs • 1st pair of appendages • Pedipals • Modified to catch and handle prey • 2nd pair of appendages • All except mites are carnivores • Only able to consume liquid food

14. Spiders • Chelicerae modified into fangs • Poison glands secrete toxins through fangs • Toxins kill or paralyze fangs • Enzymes are then injected to digest tissues into liquids • 2 dangerous Species in the U.S.: • Black widow • Brown recluse • Spinnerets • Sticky strands of silk

15. Scorpions and Mites • Chelicerae and pedipalps are modified differently

16. Scorpions • Long, slender, segmented abdomens • Abdomen ends in a venomous stinger • Used to stun prey • Pedipalps • Large, grasping pinchers • Used for capturing food • Used during reproduction

17. Mites • Largest group of arachnids • Includes chiggers and ticks • Head, thorax and abdomen are fused • Unsegmented bodies • Aquatic mites • herbivores • Terrestrial mites • carnivores • Mites can affect plants and animals • Mites can pass viral and fungal infections to plants • Lyme disease is spread by infected deer ticks

18. Section 3 Insects and Their Relatives

19. Insect Diversity • Terrestrial arthropods have chewing mouthparts (Mandibles) • Insects, millipedes, and centipedes • Insects are the largest group on earth • 700,000 named species • Many to still be discovered in the tropics • 50% of all animal species are insects

20. Insect Body Plan • Head • Mandibles (specialized mouthparts) • 1 pair of antennae • Large compound eyes • Thorax • 3 fused segments • 3 pairs of jointed walking legs • 1 or 2 pairs of wings • Abdomen • 9-11 segments • No legs • No wings

21. Insect Life Cycle • Metamorphosis • The last molt a young insect undergoes • Dramatic changes • Complete metamorphosis • Eliminates competition between adults and young • Chrysalis • Protective capsule that encloses the wingless, wormlike larva of a young insect • Pupa • Stage passed through while inside the chrysalis as it changes to adult form • Incomplete metamorphosis • Egg hatches into juvenile • Nymph • Small wingless adult • Develops through several molts

22. Flight • Insects were first animals to have wings • Allowed for greater evolution • Wings composed of chitin • Protrude from thorax • Strengthened by veins • Fold over abdomen • Some insects are wingless • Fleas and lice • Usually only 1 pair of wings are used for flight

23. Social Insects • Hymenoptera (ants, bees and wasps) and Isoptera (termites) have elaborate social systems • Many genetically related animals living together • Caste • Role played by a particular member

24. Insect Relatives • Centipedes and millipedes have similar bodies to insects • Head region followed by segments • Differ in number of legs • Centipedes • Carnivores • Millipedes • Herbivores

25. Section 4 Crustaceans

26. Crustacean Habitats • Found throughout the world’s waters (oceans) • “Insects of the sea” • Fresh or saltwater • Naupilus • Larval stage of many crustaceans • 3 pairs of branched appendages • Undergoes a series of molts before becoming adult • Mandibles • Differences • p. 680 – Table 2

27. Terrestrial Crustaceans • Pill bugs and sow bugs • Only true terrestrial crustaceans • Found in leafy ground litter • Gardens and wooded areas • Land crabs slightly terrestrial • Life cycle tied to the ocean

28. Aquatic Crustaceans • Key food source in many food chains • Humans and animals • Krill • One of the main food sources for many marine species

29. Decapods • Shrimps, lobsters, crabs, crayfish • Five pairs of legs • Head and thorax are fused • cephalothorax • Protected by carapace • Chelipeds • pinchers • Appendages called swimmerets • Uropods • Paddle-like appendage at end of abdomen

30. Sessile Crustaceans • Barnacles • Sessile as adults • Hard plate protects adults • Feathery legs stir food into the mouth • Hermaphrodites • Do not fertilize their own eggs