ArthropodsStaring the Crayfish

Part 1 – Introduction & External Anatomy

There are Four Main Groups of Arthropods

• Crustaceans (crayfish, lobsters, shrimp)

• Centipedes & Millipedes

• Arachnids (spiders)

• Insects (bugs, beetles, butterflies, grasshoppers, etc.)

Crayfish – External Anatomy

• Crayfish are crustaceans

• Have an exoskeleton (2 parts)– Cephalothorax– Abdomen

• The part that covers the cephalothorax is called the carapace

Cephalothorax Abdomen

• 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.

The long antennae are organs for touch, taste, and smell.

The antennules are organs of balance, touch, and taste.

The mandibles, or jaws, crush food by moving from side to side.

Two pairs of maxillae hold solid food, tear it, and pass it to the mouth.

• 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.

The first 3 appendages on the chephalothorax are maxillipeds.

They hold food during eating.

The chelipeds are the large claws that the crayfish uses for defense and to capture prey.

Each of the four remaining segments contains a pair of

walking legs.

The first 5 segments of the abdomen each have a pair of

swimmerets.

• The swimmerets create water

currents and help with reproduction.

• Females attach eggs to the last three pairs of swimmerets.

The 6th segment of the abdomen has a pair of flippers or uropods.

In the middle of the uropods is the telson.

On the ventral side of the telson is the anus.

• The uropod and telson together make up the tail fan.

• The crayfish moves backward by forcing water forward with its tail fan.

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.

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.

Genital Pore