Phylum Arthropoda

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Phylum Arthropoda
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Arthropod Classifications Four main lines, which
most zoologists recognize as 4 distinct subphyla
(some list these as Classes) 1. Trilobita -
extinct trilobites 2. Chelicerata - horseshoe
crabs, spiders, ticks, mites, and some extinct
groups 3. Crustacea - crabs, lobsters, shrimps,
barnacles 4. Uniramia - insects, centipedes,
millipedes
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• The Arthropod Exoskeleton
• Epidermis secretes an external skeleton called
  the exoskeleton
• Advantages of possessing an exoskeleton
• strong support
• muscles can attach to and pull against it
• protectionagainst predators, and infection
• prevents internal tissues from drying out,
  esp. on land
• Dis-Advantages
• does not grow as the animal does must molt

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• Gills
• Many aquatic arthropods (crabs and lobsters) -
  folds of tissue with a large surface area

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• Reproduction
• Sexes are separate fertilization is external in
  aquatic forms, internal among the terrestrial
  forms

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Arthropod Diversity
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• SubPhylum Crustacea
• Abdomen is also highly variable, but it is
  primitively large
• Groups with a well-developed abdomen usually
  possess six pairs of appendages Five pairs of
  structures called swimmerets
• Open circulatory system (no blood vessels)

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Crustacean Diversity
Ostracod
Water flea
Copepod
Fairy shrimp
Fish louse
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Barnacles are Crustaceans!