Arthropods

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 together by hinges Continuous 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? • Spider • Beetle • Crab • Dragonfly Correct!

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 • modified into pincers (hold food) or fangs (inject poison) chelicerae

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 eggs, eggs hatch • some look like miniature adults • will molt several times until adult size Molt Nymph Eggs Nymph Molt Adult

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

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

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 • scavengers • decomposers • parasites Predators!

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

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