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Chapter 30. Arthropods. Section 1. Features of Arthropods. 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

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chapter 30

Chapter 30

Arthropods

section 1

Section 1

Features of Arthropods

jointed appendages
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
arthropod diversity
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
arthropod body plan
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
segmentation
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

compound eye
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
exoskeleton
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

molting
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
respiration
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
excretion
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
section 2

Section 2

Spiders and Other Arachnids

arachnid modifications
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
spiders
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
scorpions and mites
Scorpions and Mites
  • Chelicerae and pedipalps are modified differently
scorpions
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
mites
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
section 3

Section 3

Insects and Their Relatives

insect diversity
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
insect body plan
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
insect life cycle
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
flight
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
social insects
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
insect relatives
Insect Relatives
  • Centipedes and millipedes have similar bodies to insects
    • Head region followed by segments
  • Differ in number of legs
  • Centipedes
    • Carnivores
  • Millipedes
    • Herbivores
section 4

Section 4

Crustaceans

crustacean habitats
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
terrestrial crustaceans
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
aquatic crustaceans
Aquatic Crustaceans
  • Key food source in many food chains
    • Humans and animals
  • Krill
    • One of the main food sources for many marine species
decapods
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
sessile crustaceans
Sessile Crustaceans
  • Barnacles
    • Sessile as adults
    • Hard plate protects adults
    • Feathery legs stir food into the mouth
    • Hermaphrodites
      • Do not fertilize their own eggs
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