Biology - Chapter 28 “Arthropods”

1. Biology - Chapter 28“Arthropods” Charles Page High School Stephen L. Cotton

2. Section 28-1Introduction to Arthropods • OBJECTIVES: • Describe the four subphyla of arthropods.

3. Section 28-1Introduction to Arthropods • OBJECTIVES: • Explain how arthropods perform their essential life functions.

4. Section 28-1Introduction to Arthropods • OBJECTIVES: • Discuss metamorphosis in arthropods.

5. Section 28-1Introduction to Arthropods • Phylum Arthropoda - vary enormously in size, shape, and habits • More than a million arthropod species have been described, and scientists are certain many more have not yet been found (such as in the tropics)

6. Section 28-1Introduction to Arthropods • Phylum Arthropoda is subdivided into four subphyla: • 1. Subphylum Trilobita • trilobites are thought to be the oldest subphylum • these were dwellers in ancient seas; they are now all extinct

7. Section 28-1Introduction to Arthropods • Phylum Arthropods is subdivided into four subphyla: • 2. Subphylum Chelicerata • chelicerates include spiders, ticks, mites, scorpions, and horseshoe crabs

8. Section 28-1Introduction to Arthropods • Phylum Arthropods is subdivided into four subphyla: • 3. Subphylum Crustacea • crustaceans include such familiar (and edible) organisms as crabs, shrimp, crayfish

9. Section 28-1Introduction to Arthropods • Phylum Arthropods is subdivided into four subphyla: • 4. Subphylum Uniramia • includes most arthropods: centipedes, millipedes, and all insects (bees, moths, flies, grasshoppers, beetles)

10. Section 28-1Introduction to Arthropods • Why are there so many? • Been evolving on Earth for a long time; the first appeared in the sea more than 600 million years ago • colonized all parts of the sea and most freshwater habitats, as well as the land

11. Section 28-1Introduction to Arthropods • The ancestors of the arthropods were soft-bodied animals that left few fossils • early forms are thought to be similar to that of the trilobites • a thick, tough outer covering, and composed of many segments with appendages

12. Section 28-1Introduction to Arthropods • The appendages were branched into one walking leg and one gill • Figure 28-3, page 608 • Most today exhibit two trends away from trilobites: • 1. Fewer body segments • 2. Appendages more specialized

13. Section 28-1Introduction to Arthropods • Although there are many different types of arthropods, they all have three important arthropod features: • 1. Tough exoskeleton • 2. Series of jointed appendages • 3. Segmented body

14. Section 28-1Introduction to Arthropods • Also have: • brain, located in dorsal part of head • ventral nerve cord • open circulatory system, powered by a single heart

15. Section 28-1Introduction to Arthropods • The exoskeleton is made of chitin (a protein) • some are leathery and flexible • others are extremely hard • exoskeleton provides protection from physical damage and also support; many are waterproof

16. Section 28-1Introduction to Arthropods • Although the exoskeleton acts like a “suit of armor”, it has some disadvantages • cannot grow as the animal grows • movement only at the joints • very heavy if the animal was to grow large

17. Section 28-1Introduction to Arthropods • All arthropods have jointed appendages (arthro- means joint; -pod means foot) that enable them to move • remaining appendages evolved into adaptations for different environments: antennae; claws; walking legs; wings; flippers

18. Section 28-1Introduction to Arthropods • All arthropods have segmented bodies • some have worm-like bodies, such as centipedes and millipedes • others have lost some of the body segments, or have fused them together, such as insects

19. Section 28-1Introduction to Arthropods • 1. Feeding- almost any type of food we can imagine • herbivores; carnivores; parasites; filter feeders; detritus feeders (Figure 28-6, p.610) • some herbivores are selective, and others will eat just about anything green

20. Section 28-1Introduction to Arthropods • 2. Respiration- 3 basic types of respiratory structures: • a) gills; b) book gills and book lungs; and c) tracheal tubes • many aquatic varieties, such as crabs and shrimp, have gills that look like a row of feathers under cover of their exoskeleton

21. Section 28-1Introduction to Arthropods • The gills are formed from the same structures as the mouthparts and legs • movement of the mouthparts and legs keeps a steady stream of water moving over the gills

22. Section 28-1Introduction to Arthropods • Book gills (found in the horseshoe crabs) and book lungs (found in spiders and relatives) are unique to these arthropods • several sheets of tissue are layered like pages of a book; this increases the surface area for gas exchange

23. Section 28-1Introduction to Arthropods • An opening called the spiracle connects the sac containing the book lungs with the fresh air outside • Most terrestrial arthropods (insects for example) have another unique structure- long branching tracheal tubes

24. Section 28-1Introduction to Arthropods • From spiracles, long branching tracheal tubes reach deep into the animal’s tissues • supplies oxygen by diffusion • as they move, body muscles cause the tracheae to shrink and expand; thus filling with air; works well in small animals

25. Section 28-1Introduction to Arthropods • 3. Internal transport- a well developed heart pumps blood through an open circulatory system • blood leaves the vessels, and moves through spaces in the tissue called sinuses

26. Section 28-1Introduction to Arthropods • 4. Excretion- solid waste leaves through the anus • nitrogen-containing wastes from cellular metabolism are removed in a variety of ways • a) insects and spiders have Malpighian tubules that filter the blood

27. Section 28-1Introduction to Arthropods • b) aquatic arthropods have wastes diffuse into the surrounding water at unarmored places, such as gills • c) some, such as lobster, have a green gland located near the base of the antennae; emptied through openings on head

28. Section 28-1Introduction to Arthropods • 5. Response- many have well developed nervous systems • all have a brain, consisting of a pair of ganglia in the head; this is the central switchboard for incoming information and outgoing instructions

29. Section 28-1Introduction to Arthropods • Nerve cord runs on ventral side of the body; along this nerve cord are additional ganglia that serve as local command centers • these coordinate legs and wings; this is why they might still move even though the head has been cut off!

30. Section 28-1Introduction to Arthropods • Simple sense organs such as statocysts and chemical receptors • also have compound eyes; more than 2000 separate lenses; can detect color and movement very well • may see ultraviolet light

31. Section 28-1Introduction to Arthropods • May have well-developed sense of taste, although the receptors are located in strange places • not only on the mouthparts, but also on antennae and legs

32. Section 28-1Introduction to Arthropods • Many insects have well-developed ears that hear sounds above the human range, but the ears are in odd places • eardrums in grasshoppers, for example, are behind their legs • spiders are sensitive to vibrations in their webs

33. Section 28-1Introduction to Arthropods • The arthropods well-developed sense organs allow it to detect and escape predators • this is in combination with their protective exoskeleton • but, there are also additional methods of protection

34. Section 28-1Introduction to Arthropods • Venomous stings- bees, ants • powerful claws- lobsters, crabs • nasty chemicals- millipedes • creating a diversion- drop claw • visual trickery- matching color and texture of surroundings • imitate other dangerous species- called mimicry (p.614)

35. Section 28-1Introduction to Arthropods • 6. Movement- well-developed muscle systems coordinated by nervous system (Figure 28-13, p.614) • the pull of muscles on the exoskeleton allows them to beat wings to fly; push legs to walk or jump; or beat flippers against water to swim

36. Section 28-1Introduction to Arthropods • 7. Reproduction- usually very simple • male produces sperm; female produces egg • fertilization usually takes place inside the body of the female • ** Stop Day #1

37. Section 28-1Introduction to Arthropods • Growth and Development- the exoskeleton (as useful as they are), present a problem in growth • it does not grow as the animal does; thus must be replaced • arthropods will molt, or shed their exoskeleton; controlled by several hormones

38. Section 28-1Introduction to Arthropods • Steps in molting: • 1. Produce molting hormone • 2. Digest inner parts of exoskeleton to recycle chemicals • 3. Form new exoskeleton; shed old exoskeleton • 4. Harden new exoskeleton

39. Section 28-1Introduction to Arthropods • The animal must wait for the new exoskeleton to harden; may only be a few hours or a few days • quite vulnerable during this time; thus they might need to hide from predators

40. Section 28-1Introduction to Arthropods • This molting may take place several times • in most cases, it will involve metamorphosis- a change in form • there are two forms of metamorphosis

41. Section 28-1Introduction to Arthropods • Metamorphosis: • 1. Incomplete metamorphosis hatches eggs into young animals that look like small adults; lack functioning sexual organs and wings • Figure 28-15, page 615 for the grasshopper on the left

42. Section 28-1Introduction to Arthropods • Metamorphosis: • 2. Complete metamorphosis involves four stages: • a) the egg • b) larvae (a wormlike stage that does not look like the adults) • c) pupa (an inactive stage that totally rearranges the body) • d) the adult

43. Section 28-1Introduction to Arthropods • Hormone interaction: • high levels of juvenile hormone keep an insect in the larval form; when it drops below a certain point- it becomes pupa • molting hormone controls the molting process

44. Section 28-1Introduction to Arthropods • Because of the balance of juvenile hormone, molting hormone, and others- it is possible to combat insects by tampering with their hormone levels • can prevent molting; thus no adults, and no reproduction!

45. Section 28-2Spiders and their Relatives • OBJECTIVES: • Discuss the distinguishing characteristics of chelicerates.

46. Section 28-2Spiders and their Relatives • OBJECTIVES: • Describe and give examples of members of the two main groups of animals in the subphylum Chelicerata.

47. Section 28-2Spiders and their Relatives • OBJECTIVES: • Explain how arachnids obtain food.

48. Section 28-2Spiders and their Relatives • Subphylum Chelicerata- called chelicerates, includes spiders and their relatives- horseshoe crabs, ticks, and scorpions • characterized by a two-part body and mouthparts called “chelicerae”

49. Section 28-2Spiders and their Relatives • also lack sensory “feelers” found on the heads of most other arthropods • the two-part body is: • 1. Cephalothorax • 2. Abdomen

50. Section 28-2Spiders and their Relatives • Cephalothorax- contains the brain, eyes, mouth and mouthparts, and esophagus • posterior end is the first part of the digestive system, and several pairs of walking legs • Abdomen- contains most of the internal organs (Fig. 28-17, p.617)