Chapter 30
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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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