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Chapter 30

Chapter 30. Arthropods. I. Features of Arthropods. A typical arthropod is a segmented , coelomate invertebrate animal with bilateral symmetry, an exoskeleton , and jointed structures called appendages. A. Jointed appendages: “joint foot”=arthropoda

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Chapter 30

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  1. Chapter 30 Arthropods

  2. I. Features of Arthropods • A typical arthropod is a segmented, coelomate invertebrate animal with bilateral symmetry, an exoskeleton, and jointed structures called appendages. • A. Jointed appendages: • “joint foot”=arthropoda • An appendage is any structure, such as a leg , an antenna, or mouthpart that grows out of the body of an animal. Section 28.1 Summary – pages 741 - 746

  3. What is an arthropod? • Joints also allow powerful movements of appendages, and enable an appendage to be used in many different ways. • Mouthparts have sucking, ripping or chewing parts Section 28.1 Summary – pages 741 - 746

  4. Origins of Arthropods Section 28.2 Summary – pages 747 - 755

  5. Origins of Arthropods • Arthropods most likely evolved from an ancestor of the annelids. • Oldest, best –preserved • multicellular animal fossils • 600 million years old • Most numerous early arthropod: trilobites • -became extinct about 250 million years ago • Lived in the sea • Segmented bodies • Jointed appendages • First animals with eyes capable of forming images. • First terrestrial arthropods: scorpions Section 28.2 Summary – pages 747 - 755

  6. The total number of arthropods • Exceeds that of all other kinds of animals • combined . • 5,000,000 species • More species of beetles than vertebrates. • Size varies from 80 micrometers (parasitic mite)- to 3.6 m (giant crab found in the sea near Japan.) Section 28.2 Summary – pages 747 - 755

  7. Two main groups • Arthropods with jaws • 1.-Uniramia – (subphylum) insects • chilopoda and diplopoda • 2. Crustacea- (subphylum) shrimp, crab lobster • Arthropods with fangs and pincers • 1. Chelicerata (subphylum) – scorpions, mites, • spiders • ***Each subphyla represents a distinct evolutionary line.

  8. Arthropod Body Plan Segmentation in arthropods • In most groups of arthropods, segments have become fused into three body sections—head, thorax (mid body region), and abdomen. • Individual body segments often exist only in larval stages. (ex: catepillar) Section 28.1 Summary – pages 741 - 746

  9. Segmentation in arthropods • In other groups, even these segments may be fused. • Some arthropods have a head and a fused thorax and abdomen. Section 28.1 Summary – pages 741 - 746

  10. Segmentation in arthropods • In other groups, there is an abdomen and a fused head and thorax called a cephalothorax. • Fusion of the body segments is related to movement and protection. Section 28.1 Summary – pages 741 - 746

  11. Arthropods have acute senses • A compound eye is a visual structure with many lenses. • See motion much more quickly than humans. Section 28.1 Summary – pages 741 - 746

  12. Accurate vision is also important to the active lives of arthropods. • Most arthropods have one pair of large compound eyes and three to eight simple eyes. • A simple eye is a visual structure with only one lens that is used for detecting light. • In dragonflies and locusts, these simple eyes function as horizon detectors. –helps them stabilize their position in flight. Section 28.1 Summary – pages 741 - 746

  13. Arthropod exoskeletons provide protection • The exoskeleton is a hard, thick, outer covering made of protein and chitin (KI tun). • Brittle and can break easily Section 28.1 Summary – pages 741 - 746

  14. Arthropod exoskeletons provide protection • In some species, the exoskeleton is a continuous covering over most of the body. • In other species, the exoskeleton is made of separate plates held together by hinges. • Crustaceans : thick relatively inflexible exoskeleton. • Insects and arachnids: soft and flexible exoskeleton. Section 28.1 Summary – pages 741 - 746

  15. Arthropod exoskeletons provide protection • The exoskeleton protects and supports internal tissues and provides places for attachment of muscles. • In many aquatic species, the exoskeletons are reinforced with calcium carbonate. Section 28.1 Summary – pages 741 - 746

  16. Why arthropods must molt • Exoskeletons have their disadvantages. • First, they are relatively heavy structures. The larger an arthropod is, the thicker and heavier its exoskeleton must be to support its larger muscles. Section 28.1 Summary – pages 741 - 746

  17. Why arthropods must molt • A second and more important disadvantage is that exoskeletons cannot grow, so they must be shed periodically. Shedding the old exoskeleton is called molting. Section 28.1 Summary – pages 741 - 746

  18. Why arthropods must molt • When the new exoskeleton is ready, the animal contracts muscles and takes in air or water. • This causes the animal’s body to swell until the old exoskeleton splits open, usually along the back. Section 28.1 Summary – pages 741 - 746

  19. Why arthropods must molt • Before the new exoskeleton hardens, the animal puffs up as a result of increased blood circulation to all parts of its body. • Thus, the new exoskeleton hardens in a larger size, allowing some room for the animal to continue to grow. Section 28.1 Summary – pages 741 - 746

  20. Why arthropods must molt • Most arthropods molt four to seven times in their lives before they become adults. • When the new exoskeleton is soft, arthropods cannot protect themselves from danger because they move by bracing muscles against the rigid exoskeleton. Section 28.1 Summary – pages 741 - 746

  21. Respiration: Arthropods have efficient gas exchange • Arthropods have efficient respiratory structures that ensure rapid oxygen delivery to cells. • This large oxygen demand is needed to sustain the high levels of metabolism required for rapid movements. Section 28.1 Summary – pages 741 - 746

  22. Arthropods have efficient gas exchange • Three types of respiratory structures have evolved in arthropods: gills, tracheal tubes, and book lungs. Section 28.1 Summary – pages 741 - 746

  23. Arthropods have efficient gas exchange • Aquatic arthropods exchange gases through gills, which extract oxygen from water and release carbon dioxide into the water. Section 28.1 Summary – pages 741 - 746

  24. Arthropods have efficient gas exchange • Land arthropods have either a system of tracheal tubes or book lungs. Section 28.1 Summary – pages 741 - 746

  25. Arthropods have efficient gas exchange • Most insects have tracheal tubes, branching networks of hollow air passages that carry air throughout the body. Section 28.1 Summary – pages 741 - 746

  26. Arthropods have efficient gas exchange • Muscle activity helps pump the air through the tracheal tubes. • Air enters and leaves the tracheal tubes through openings on the thorax and abdomen called spiracles. Section 28.1 Summary – pages 741 - 746

  27. Arthropods have efficient gas exchange • Most spiders and their relatives have book lungs, air-filled chambers that contain leaflike plates. Section 28.1 Summary – pages 741 - 746

  28. Arthropods have efficient gas exchange • The stacked plates of a book lung are arranged like pages of a book. Section 28.1 Summary – pages 741 - 746

  29. Excretion: • Most terrestrial arthropods excrete wastes through Malpighian tubules. • Slender, fingerlike extensions from the arthropods gut that are bathed in blood. • In insects, the tubules are all located in the abdomen rather than in each segment. • Malpighian tubules are attached to and empty into the intestine. • Metabolic wastes remain in the gut and leave the body through the anus. Section 28.1 Summary – pages 741 - 746

  30. II. Spiders and other Arachnids Section 28.2 Summary – pages 747 - 755

  31. What is an arachnid? • Spiders, scorpions, mites, and ticks belong to the class Arachnida (uh RAK nud uh). • Spiders are the largest group of arachnids. • Spiders and other arachnids have only two body regions—the cephalothorax and the abdomen. • They have no antennae • Arachnids have six pairs of jointed appendages. Section 28.2 Summary – pages 747 - 755

  32. What is an arachnid? • The first pair of appendages, called chelicerae,islocated near the mouth. Section 28.2 Summary – pages 747 - 755 chelicerae

  33. What is an arachnid? • Chelicerae are often modified into pincers or fangs. • Pincers are used to hold food, and fangs inject prey with poison. Section 28.2 Summary – pages 747 - 755

  34. What is an arachnid? • Spiders have no mandibles for chewing. • Using a process of extracellular digestion, digestive enzymes from the spider’s mouth liquefy the internal organs of the captured prey. The spider then sucks up the liquefied food. Section 28.2 Summary – pages 747 - 755

  35. What is an arachnid? • The second pair of appendages, called the pedipalps, are adapted for handling food and for sensing. pedipalps • Sometimes the pedipelps are for reproduction. • Following the pedipalps, are 4 pairs of appendages called walking legs. Section 28.2 Summary – pages 747 - 755

  36. What is an arachnid? • Although all spiders spin silk, not all make webs. • Spider silk is secreted by silk glands in the abdomen. Section 28.2 Summary – pages 747 - 755

  37. What is an arachnid? • As silk is secreted, it is spun into thread by structures called spinnerets, located at the rear of the spider. Section 28.2 Summary – pages 747 - 755

  38. A Spider Legs Simple eyes Cocoon Silk glands Book Lungs Pedipalps Chelicerae • Spiders are predatory animals, feeding almost exclusively on other arthropods.(=carnivores) Section 28.2 Summary – pages 747 - 755

  39. Ticks, mites, and scorpions: Spider relatives • Ticks and mites differ from spiders in that they have only one body section. Section 28.2 Summary – pages 747 - 755 tick

  40. Ticks, mites, and scorpions: Spider relatives • The head, thorax, and abdomen are completely fused. • Plant mites- while feeding may pass viral and fungal infections to plants. • Dust mites- live in carpet, bedding, clothing. (cause allergies) • Chiggers-known for their irritating bite Section 28.2 Summary – pages 747 - 755 • Ticks feed on blood from reptiles, birds, and mammals.

  41. Ticks, mites, and scorpions: Spider relatives • Mites feed on fungi, plants, and animals. • They are so small that they often are not visible to the unaided human eye. • Like ticks, mites can transmit diseases. • Lyme disease is spread by deer ticks Section 28.2 Summary – pages 747 - 755

  42. Ticks, mites, and scorpions: Spider relatives • Scorpions are easily recognized by their many abdominal body segments and enlarged pincers.(=pedipalps) • They have a long tail with a venomous stinger at the tip. Which is used to stun their prey. Section 28.2 Summary – pages 747 - 755

  43. Insects • Flies, grasshoppers, lice, butterflies, bees, and beetles are just a few members of the class Insecta. • Insects have three body segments (head thorax and abdomen) and six legs. • Head- mandibles (chewing mouth part) pair of antennae, compound eyes • Thorax - (composed of 3 fused segments.) • 3 pair of jointed walking legs and some have wings that are attached to the thorax. • Abdomen- is composed of 9-11 segments Section 28.2 Summary – pages 747 - 755

  44. Arthropods have other complex body systems • The mandibles, together with other mouthparts are adapted for holding, chewing, sucking, or biting the various foods eaten by arthropods. Section 28.1 Summary – pages 741 - 746

  45. A Grasshopper Antennae Legs Eyes Wings Spiracles Section 28.2 Summary – pages 747 - 755 Malpighian tubules Tympanum Nervous System

  46. Insect reproduction/Life Cycle • Insects usually mate once during their lifetime. • The eggs usually are fertilized internally. • Some insects exhibit parthenogenesis, reproducing from unfertilized eggs. Section 28.2 Summary – pages 747 - 755

  47. Insect reproduction • Most insects lay a large number of eggs, which increase the chances that some offspring will survive long enough to reproduce. Section 28.2 Summary – pages 747 - 755

  48. Metamorphosis: Change in body shape and form • After eggs are laid, the insect embryo develops and the eggs hatch. • In some wingless insects development is direct; the eggs hatch into miniature forms that look just like tiny adults. Section 28.2 Summary – pages 747 - 755

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