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

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

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)

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

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

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

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

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

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

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

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

Circulatory System The crayfish has an open circulatory system

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

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

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

Nervous System Very simple Nerves carry impulses to the brain

Nervous System Ventral nerve cord carries messages to the body

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.

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

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

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

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.

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

Genital Pore

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