1. Staring the Crayfish Part 2 – Internal Anatomy
Arthropods
Staring the Crayfish
Part 2 – Internal Anatomy

2. Hold on a minute!
Why do we dissect animals anyway?

3. Why dissect?
It is important to learn the similarities and differences between animals – so that we can know about ourselves better.
Analogous = organs in different animals that have similar functions (gills vs. lungs)
Homologous = animals that share the same organs (frog and human liver)

7. Nutrition & the Digestive System
The jaws tear the food apart and it passes down a short esophagus to the stomach

8. Nutrition & the Digestive System
The stomach has 3 teeth made of chitin to grind the food

9. Nutrition & the Digestive System
The cardiac stomach grinds the food
The fine pieces of food are passes to the next stomach, called the pyloric stomach
In the pyloric stomach, digestive juices are mixed with the food

10. Nutrition & the Digestive System
Digested food is passed to the digestive glands where nutrients are absorbed

11. Nutrition & the Digestive System
Undigested food goes to the intestines where it is eliminated as feces through the anus.

12. Excretory System
The green glands filter and excrete waste from the blood.
They are located at the base of the antennae.

13. Respiratory System
The gills are feather like structures found underneath the carapace
Very thin walled
They are attached to the chelideds and walking legs.
A constant flow of blood to the gills releases carbon dioxide and picks up oxygen

14. Respiratory System
The feathery nature of the gills give them a very large surface area. Why is this important?

15. Circulatory System
The crayfish has an open circulatory system

16. Circulatory System
The blood leaves the dorsal heart through a series of arteries.

17. Circulatory System
After leaving the heart, the blood flows into sinuses, or spaces, in the tissues
The blood picks up nutrients from the digestive gland and oxygen from the gills and carries them to the cells
The blood flows over the gills picking up more oxygen and releasing carbon dioxide before returning to the heart

18. Circulatory System Why do the cells need oxygen & nutrients?
Why do the cells produce carbon dioxide?

19. Nervous System
Very simple
Nerves carry impulses to the brain

20. Nervous System
Ventral nerve cord carries messages to the body

21. Nervous System There are ganglia throughout the body
Many nerves leave from each ganglion
Where do you think these nerves go?
Statocysts are organs used for balance. They are filled with sand and sensory bristles. They are in the base segments of the antennae.

22. Reproduction & Growth
Crayfish have separate male and female animals ~ in other words, they are not hermaphrodites
External Fertilization = eggs are fertilized outside of the female’s body
Fertilized eggs are stored on the last three abdominal sections on the female

23. Reproduction & Growth Eggs will hatch in 6 to 8 weeks
As the crayfish gets larger, it must molt, or shed its exoskeleton
It molts several times during the first year and about twice per year thereafter
The crayfish is very vulnerable after molting until its exoskeleton becomes hard once again

24. Reproduction & Growth Crayfish can live 3 to 4 years
They can regenerate, or regrow, lost appendages

25. 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.

26. Reproductive System - Female
Female = observe a crescent-shape slit on the base segment of the 3rd walking leg (genital pore)

27. Genital Pore

28. Reproductive System - Male
Male = sperm duct opening on the base segment of 4th pair of walking leg.