Arthropod Notes

Phylum Arthropoda

  • Segmented with jointed appendages.
  • Exoskeleton for protection and support; waxy coating prevents water loss.
  • High degree of cephalization with segmented appendages, antennae, and compound eyes.
  • Ventral nerve cord.
  • Open circulatory systems.
  • Molting is required for growth; arthropods are vulnerable during this process.

Evolution and Classification

  • Evolved from ancestors with a coelom, exoskeleton, and jointed appendages.
  • Have tagmata (fused segments) for specialized functions.
    • Trilobita: Extinct; paired appendages.
    • Crustacea: Shrimps, lobsters, crabs; branched antennae, mandibles.
    • Chelicerata: Spiders, scorpions; chelicerae (pincer-like mouthparts), no antennae.
    • Uniramia: Centipedes, millipedes, insects; antennae, mandibles, unbranched appendages.

Subphylum Crustacea

  • Two pairs of antennae.
  • Aquatic species have calcium carbonate in exoskeletons.
  • Nauplius larva during development.
  • Gas exchange via exoskeleton or gills.
  • Decapods like crayfish have 5 pairs of legs.

Crayfish External Structure

  • Cephalothorax (head and thorax with carapace) and abdomen (with telson).
  • Abdomen facilitates tailflips.
  • Antennules and antennae for touch/taste/equilibrium.
  • Mandibles, maxillae, and maxillipeds for chewing/manipulation.
  • Pinchers for food capture/defense.
  • Swimmerets for water currents and reproduction.
  • Uropods aid tailflips.

Crayfish Systems

  • Digestion: Chitin teeth grind food, enzymes from digestive gland, anus for waste.
  • Respiration: Gills under carapace, legs circulate water.
  • Circulation: Dorsal heart pumps hemolyph in open system.
  • Excretion: Green glands excrete excess water.

Crayfish Neural Control

  • Brain: Ganglia above esophagus receive impulses from eyes/antennae.
  • Ventral nerve cord controls appendages/muscles.
  • Sensory hairs detect vibrations/chemicals.
  • Compound eyes with light-sensitive units.

Subphylum Chelicerata and Uniramia

  • Arachnida: Spiders, scorpions, mites, ticks; cephalothorax and abdomen.
  • Six pairs of appendages: chelicerae (fangs), pedipalps, four pairs of walking legs.

Spider Anatomy and Life

  • Chelicerae inject venom.
  • Eight simple eyes.
  • Spinnerets produce silk.
  • Book lungs/tracheae for respiration via spiracles.
  • Malpighian tubules for excretion.
  • Catch prey using webs, chasing, or trap doors; paralyze with venom.
  • Black Widow and Brown Recluse are dangerous.

Scorpions and Mites/Ticks

*Scorpions: Large pincer-like pedipalps, stinger on abdomen.

  • Mites and Ticks: Cephalothorax and abdomen are fused, parasitic ticks spread disease.

Myriapods (Uniramia)

  • Millipedes and centipedes in Uniramia, single pair of antennae.
  • Require moist environments.
  • Millipedes (Diplopoda): Two pairs of legs per segment, feed on decaying plants, secrete cyanide.
  • Centipedes (Chilopoda): One pair of legs per segment, poison claws, tear prey apart.