Name:_________________________ Lab Partner(s):________________
Blk:_________
Kingdom Animalia
Phylum Arthropoda: Crayfish dissection
Pre-lab Discussion:
Like all crustaceans, a crayfish has a fairly hard exoskeleton that covers
its body. The crayfish body is divided into two main parts, the
cephalothorax and the abdomen. The cephalothorax consists of the cephalic
region and the thoracic region. The part of the exoskeleton that covers the
cephalothorax is called the carapace. The abdomen is located behind the
cephalothorax and consists of six clearly divided segments. The
cephalothorax consists of 13 segments. Each segment of both the
cephalothorax and the abdomen contains a pair of appendages.
The head (or cephalic) region has five pairs of appendages.
The antennules are organs of balance, touch, and taste. Long antennae are
organs for touch, taste, and smell. 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.
Of the eight pairs of appendages on the cephalothorax, the first three
are maxillipeds, which 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. In the abdomen, the
first five segments each have a pair of swimmerets, which create water
currents and function in reproduction. The sixth segment contains a modified
pair of uropods.In the middle of the uropods is a structure called
the telson, which bears the anus. The uropod and telson together make up
the tail fan. The crayfish moves backward by forcing water forward with
its tail fan.
Lab Assignment:
Following the procedure outlined below, you are to investigate and record
observations during the dissection of a crayfish.
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Materials: (per group)
Equipment: Preserved crayfish
Safety:
Dissection tray
Scissors
Probe
Dissecting pins
Forceps
Hand lens
Paper towels
1. The pins, probe, and scissors are very sharp! Be very careful when using
these materials to ensure you do not cut yourself.
2. The preservative used for the crayfish may irritate the skin. Avoid
touching your face and eyes while performing this dissection.
Dissection tips:
1. DON’T JUST START CUTTING! – Be sure to make all
necessary observations of the external structures before you begin
dissecting your specimen
2. The exoskeleton of the crayfish is very hard and may be sharp.
When removing the exoskeleton be very careful to avoid harming
both yourself and the internal organs you need to observe.
Pre-lab Questions:
1. Which subphylum does the crayfish belong to?
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2. List 1 organ you would expect to find in the cephalic region of the
cephalothorax:
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3. List two organs you would expect to find in the thoracic region of the
cephalothorax:
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Procedure:
Part 1: External anatomy of the crayfish:
Complete each step of the checklist
 Line the dissecting tray with moist paper towels.
 Rinse the crayfish thoroughly and place it on the dissecting tray.
 Observe the difference between the ventral and dorsal surfaces of the
crayfish
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 Place the crayfish dorsal side up and, using the diagram below for
reference, locate the following structures:
 Cephalothorax
 Abdomen
 Carapace
 Rostrum
 Cervical groove (indentation which separates the head and
thoracic regions)
Obs. 1: Use the space below to draw the dorsal view of the crayfish external
anatomy. Using a ruler, indicate the length of the cephalothorax (include the
head region, the thoracic region and the whole cephalothorax) and the
abdomen.
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 Turn the crayfish on its side to observe the eyes beneath the rostrum. Notice that each eye
is on the end of a stalk.
 Locate the different pairs of appendages on the head region.
 attenules
 antennae
 mandibles
 maxillae (there are two pairs of maxillae)
 Which appendages on the cephalic region are related to the eating of food?
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 On the thoracic region of the cephalothorax, observe the pointed maxillipeds.
 Observe the largest appendages, the chelipeds (claws). Behind the chelipeds, observe the
four pairs of walking legs. There is one pair of walking legs on each segment.
 On the abdomen observe the six different segments, each containing a pair of
swimmerets.
 Observe the modified, final segment of the abdomen. This segment contains the
triangular-shaped telson between a pair of uropods.
 What is the function of the final segment of the abdomen?
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Part 2: Internal anatomy of the crayfish
Complete each step of the checklist
 Using the scissors, carefully remove the thoracic portion of the carapace as shown in
the diagram below:
**Be careful not to damage the delicate internal organs when removing the carapace.
 Locate the feather-like gills below the carapace. The gills are also attached to the
chelipeds and walking legs.
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 Which body system do the gills belong to?
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 Describe the structure of the gills. Explain how the structure relates to the function
the gills carry out.
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 Use the scissors to carefully remove the cephalic (head) region of the cephalothorax.
 Using the diagram below for reference, locate the stomach and heart
 Carefully remove the gills, stomach and digestive gland so that you can
observe the ventral nerve chord and brain.
Obs. 2: In the space below draw a diagram of the crayfish ventral nerve chord and brain
 In the space just posterior to the brain, observe the crayfish’s two green glands
(left and right)
 What function do these green glands serve for the crayfish?
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Part 3: Crayfish appendages
Complete each step of the checklist
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 Remove an example of each of the following appendages and observe the differences
between them. For the antennae, mandible, cheliped, and uropod explain the
function of the appendage and how it has been modified to perform this function.
 Antennule
 Antenna:
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
Function:
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Form:
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 Mandible:
 Function:
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 Form:
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 Maxilla
 Maxillaped
 Cheliped:
 Function:
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 Form:
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 Walking leg
 Swimmeret
 Uropod:
 Function:
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 Form:
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Analysis and Conclusion Questions:
1. Is the crayfish more vulnerable to its enemies from the ventral side or the dorsal side? Why?
2. What structure in humans would be analogous to the green glands of crayfish?
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3. Label the diagram below with the external structures of the crayfish:
Critical Thinking and Application
1. Compare the anatomy of the crayfish with that of an insect. List two similarities and two
differences between the anatomies of the different classes.
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2. Why is it possible for marine members of Phylum Arhtropoda to grow much larger than
terrestrial animals within the same phylum?
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3. List three specific ways that a crayfish is more complex than an earthworm.
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