Arthropods

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Arthropods

• Staring the Crayfish
• Part 1 Introduction External Anatomy

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There are Four Main Groups of Arthropods

• Crustaceans (crayfish, lobsters, shrimp)
• Centipedes Millipedes
• Arachnids (spiders)
• Insects (bugs, beetles, butterflies,
  grasshoppers, etc.)

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Crayfish External Anatomy

• Crayfish are crustaceans
• Have an exoskeleton (2 parts)
• Cephalothorax
• Abdomen
• The part that covers the cephalothorax is called
  the carapace

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Cephalothorax Abdomen
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• Each segment of both the cephalothorax and the
  abdomen contain a pair of appendages.
• The cephalothorax is divided into 13 segments
• The abdomen is divided into 6 segments
• The head region also has 5 pairs of appendages.

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The long antennae are organs for touch, taste,
and smell.
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The antennules are organs of balance, touch, and
taste.
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The mandibles, or jaws, crush food by moving from
side to side.
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Two pairs of maxillae hold solid food, tear it,
and pass it to the mouth.
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• The second pair of maxillae also helps to draw
  water over the gills.
• Crayfish need water to flow over their gills so
  that they can breathe.

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The first 3 appendages on the chephalothorax are
maxillipeds. They hold food during eating.
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The chelipeds are the large claws that the
crayfish uses for defense and to capture prey.
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Each of the four remaining segments contains a
pair of walking legs.
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The first 5 segments of the abdomen each have a
pair of swimmerets.
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• The swimmerets create water currents and help
  with reproduction.
• Females attach eggs to the last three pairs of
  swimmerets.

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The 6th segment of the abdomen has a pair of
flippers or uropods.
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In the middle of the uropods is the telson.
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On the ventral side of the telson is the anus.
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• The uropod and telson together make up the tail
  fan.
• The crayfish moves backward by forcing water
  forward with its tail fan.

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Is your crayfish a male or female?

• Locate the base segment of each pair of walking
  legs.
• The base segment is where the leg attaches to the
  body.
• Study the inside surface of the base segments of
  the 3rd and 4th walking legs.

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Male or Female?

• Female observe a crescent-shape slit on the
  base segment of the 3rd walking leg (genital
  pore)
• Male sperm duct opening on the base segment of
  4th pair of walking leg.

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Genital Pore
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