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.
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Internal Anatomy