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.