PHYLUM ARTHROPOD

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PHYLUM ARTHROPOD

• Jointed foot

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Arthropod

• 3/4 of all animal species belong to Phylum
  Arthropoda
• examples include insects, spiders, lobsters,
  and centipedes

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Basic characteristics of arthropods

• Have jointed appendages
• body is segmented
• pair of appendages is attached to each segment
• have an exoskeleton
• have a ventral nervous system, open circulatory
  system, digestive system, and specialized sensory
  receptors
• reduced competition through metamorphosis

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Movement and Growth

• Muscles occur in bundles and operate as levers
• ecdysis (molting) - shedding of exoskeleton
• tissues grow, putting pressure on the
  exoskeleton, then a hormone induces the shedding
  process
• extremely vulnerable to predators and dessication
  during this time

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Evolution and Classification

• Because of exoskeleton, they all have a common
  ancestor
• have evolved into four separate lines of
  arthropods

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4 separate lines of arthropods

• 1) Trilobita includes extinct organisms called
  trilobites
• 2) Crustacea includes shrimp, lobsters,
  crayfish, water fleas, crabs
• have branched antennae and mandibles

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4 separate lines of arthropods

• 3) Chelicerata includes spiders, scorpions,
  ticks, mites, sea spiders, and horseshoe crabs
• absence of antennae and presence of chelicerae
• 4) Uniramia only group that seems to have
  evolved on land
• includes centipedes, millipedes, all insects
• means one branch, so appendages are unbranched
• have mandibles

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