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Phylum Arthropoda

Phylum Arthropoda. “jointed foot” Chitonous exoskeleton Open circulatory system Polyphyletic or monophyletic? Merostomata, Crustacea, Trilobites – biramous Insects, centipedes, millipedes - uniramous. Segmentation. Characteristic of Arthropoda Both external and internal segmentation

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Phylum Arthropoda

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  1. Phylum Arthropoda • “jointed foot” • Chitonous exoskeleton • Open circulatory system • Polyphyletic or monophyletic? • Merostomata, Crustacea, Trilobites – biramous • Insects, centipedes, millipedes - uniramous

  2. Segmentation • Characteristic of Arthropoda • Both external and internal segmentation • Some evidence of segmentation lost • Regional specialization throughout phylum

  3. Annelid-Arthropod Link • Segmentation • Segments lost • Segments have fused • Divergence of appendages • Nervous System • Spiral determinate cleavage • Pair of appendages on each body segment

  4. Think about ancestral arthropod

  5. Tagmosis

  6. Cephalization See Figure 16-3

  7. Biramous Uniramous

  8. Fig 16-1C

  9. Fig 16-1E

  10. Figure 16-1B

  11. Coelom and Blood-Vascular System • Coelom reduced extensively (hydrostatic to rigid skeleton) • Coelom larger in embryonic development • Remnants persist with nephridia and reproductive organs • Circulatory system for transport • Combination of hemocoel and blood vessels (not present in all arthropods)

  12. Saccate Nephridia

  13. Gas Exchange • Gills (Crustacea, aquatic insects**) • Book gills (Merostomata) • Book lungs (many Arachnida) • Tracheae (all tracheates [includes insects], Onychophora, Arachnids) - convergence

  14. Down to cellular level and chitin

  15. Foregut Midgut Hindgut

  16. Cornea fixed rhodopsin mosaic image

  17. Other Sensory Structures • Mechanoreceptors • Chemoreceptors • Equilibrium receptors

  18. Subphylum Trilobitomorpha • All extinct • Present 560 through 260 mya • Marine • Diverse – occupied many niches • Most 3 – 10 cm long

  19. See also Fig 17-2A

  20. Subphylum Chelicerata

  21. Subphylum Chelicerata • Body of two tagmata (regions) • Cephalothorax (prosoma) • abdomen • Cephalothorax – acron + 7 segments • Six pair appendages • 1st appendage – chelicerae • 2nd pair – pedipalps (often sensory) • Rest are walking legs

  22. Subphylum Chelicerata • Abdomen • Primitive condition • Preabdomen (7 segments) • Postabdomen (5 segments and telson) • Varying levels of fusion of abdomen • Many terrestrial, some marine and freshwater

  23. Crustacea

  24. Subphylum Crustacea • Marine, freshwater, with a few terrestrial • Body in 2 - 3 tagmata • Head = acron + five segments (fused) • Typical is five pair of appendages (1st and 2nd antennae, 3 pr mouthparts) • 2nd antennae homologous to chelicerae • Additional fusion of thoracic segments to head in higher Crustacea

  25. Subphylum Crustacea • Thorax variable • Depends on if been additional fusion • Cephalothorax characteristic of major crustacean groups • Abdomen also variable in number of segments • Abdomenal appendages - pleiopods

  26. Class Hexapoda • Uniramous appendages (sP Uniramia) • Most successful group of metazoa • Terrestrial, also freshwater and marine • Three tagmata (H, T, A) • Head – 3 to 7 segments, probably 7 • Thorax – 3 segments (pro-, meso-, meta-) • Abdomen – 9 to 11 segments, no appendages

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