Zoology

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Zoology Chapter 31 Arthropods
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• Phylum Arthropoda
• Likely evolved from Annelids
• Common characteristics
• 1. Invertebrate
• 2. Bilateral symmetry
• 3. Coelomate

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• 4. Exoskeleton
• Exoskeleton
• 5. Jointed appendages (any structure that grows
  out of the body of an animal)
• -used for sensing, walking, feeding, mating
• Features

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• 1st invertebrates to develop appendages
• -allow for powerful coordinated movement
• -have multiple uses

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• Exoskeleton
• -hard, thick, outer covering of protein
  chitin
• -can be continuous or hinged plates
• -function - protects, supports, muscle
  attachment
• -covered w/ waxy layer in some terrestrial
  arthropods
• -key to phylas success

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• Exoskeleton disadvantages
• -heavy can limit movement
• -some land flying have thinner exoskeletons
• -molting shedding of the old exoskeleton
• -when org. grows
• -org. vulnerable until new exoskeleton
  hardens strength returns

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• Segmentation
• -not as many as segmented worms
• -3 regions
• 1. head
• 2. thorax
• 3. abdomen
• -cephalothorax-fused head thorax

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• Efficient respiratory systems
• -high metabolism that requires large amounts of
  oxygen relative to other organisms
• -3 types of respiratory structures
• A. Gills
• -aquatic arthropods

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• B. Tracheal tubes
• -network of branching air passages
• -air moved by muscle activity
• -air enters/
• leaves thru
• spiracles
• openings in
• thorax
• abdomen

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• C. Book lungs
• -found in arachnids
• -air-filled chambers w/ leaflike plates

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• Acute Senses
• -well-developed nervous system
• -compound eyes that can see in all directions
  analyze environment changes

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• -antennae are sensitive to movement, sound,
  chemicals
• -Pheromones chemical odor signals used for
  communication

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• Complex Body Systems
• -blood pumped by heart(s) in open circulatory
  system
• -complete digestive system
• -mandibles mouthparts adapted for holding,
  chewing, sucking, biting
• -contains glands that secrete various
  digestive enzymes

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• -Malpighian tubules
• -tubes in abdomen where waste is excreted
• -empty into the intestines

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• Reproduction
• -Sexual
• -Separate sexes
• -Internal on land, external in water
• -few hermaphrodites
• -parthenogenesis form of asexual reproduction,
  org develops from unfertilized egg

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• Origins
• -most likely evolved from Annelids
• -because of its hard exoskeleton, fossil record
  is fairly complete

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• Classes
• Insecta (more than 1million species)
• -Insects
• -6 legs, antennae
• 2. Crustacea (67,000 species)
• -Lobsters, Crayfish, Shrimp
• 3. Arachnids (100,000 species)
• -Spiders, Ticks, Mites, Scorpions
• -8 legs, 2 body segments

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• 4. Chilpoda (3000 species)
• -Centipedes
• -1 pair of legs per segment
• 5. Diplopoda (10,000 species)
• -Millipeds
• -2 pairs of legs per segment
• 6. Merostomata (4 species)
• -Horseshoe crabs