Download Crayfish Dissection

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CRAYFISH LAB
PART TWO: CRAYFISH DISSECTION
DISSECTION VIDEO
EXTERNAL ANATOMY
ABDOMEN
THORAX
HEAD
A. Segmentation
 Examine the external anatomy of your crayfish. Typically, arthropod bodes are divided into three sections: head thorax
and abdomen. In the crayfish, the head and the thorax are fused into a single cephalothorax. Find the cephalothorax and
abdomen of your crayfish. Notice that the crayfish has a hard external skeleton. The covering of the cephalothorax is
called the carapace.
 How many segments do you see in the abdomen?
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 What is the relationship between the external skeleton and body size?
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B. Gender  FIGURE 1
 Determine the sex of your crayfish. To do this, look at the first two pairs of swimmerets, located near the middle of the
abdomen. In the male, these are large and stiff and are used for transferring sperm to the female. In the female, they are
small, like the other swimmerets. Compare several crayfish so you see the difference between the two sexes.
 What is the sex of your crayfish? How do you know?
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C. Appendages  FIGURE 2 and FIGURE 3
 They are listed below, beginning at the head. Notice that they are jointed. This is characteristics of all arthropods.
 Remove the crayfish appendages and lay them on your tray in the order they are removed. Identify each.
 The head appendages are all mouth parts of the crayfish. It is difficult to see them individually. It helps to gently separate
them with a probe.
APPENDAGE
antennules
antennae
mandible
first maxilla
second maxilla
maxilliped (1-3)
cheliped (1st walking leg)
walking legs (2-4)
swimmerets (1-3)
males
females
uropod
DESCRIPTION & FUNCTION
two, short filamentous structures at the tip of the rostrum for touch, taste and equilibrium
two, long filamentous structures lateral to the antennules for touch and taste
bears teeth for crushing food
for food handling
food handling and bailing water from gill chamber
touch, taste and food handling; have gills for respiration
grasping food, defense and respiration
walking and respiration
circulates water
1st is modified to transfer sperm to female seminal receptacle
assists in carrying eggs and young
locomotion and protecting eggs (female only)


Remove an antennule and cut away the exoskeleton from one side of the basal (connecting) area. Locate a small sac
inside the base. This is a statocyst, an organ of equilibrium. Cut this open under the stereoscope.
 What is inside this statocyst?
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Examine the mandible under the stereoscope. Draw what you see. Examine the maxillipeds (any one) under the
stereoscope Draw what you see.
Mandible
TM: _______________
Maxilliped
TM: _______________
 What is the function of the gills?
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 What is the advantage of having gills attached to the walking legs?
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D. The Eye
 Remove the eye.
 Observe the compound eye of the crayfish under the stereoscope. They are made up of many photoreceptor units. This
makes them especially sensitive to movement. Compound eyes are characteristic of arthropods.
 Draw the eye:
TM :______________

Cut the eye longitudinally. You should be able to see the optic ganglion (large, grayish mass).
 Why is this type of eye well-suited to the crayfish’s nocturnal lifestyle?
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INTERNAL ANATOMY
E. Fist Cuts  FIGURE 4
 Use scissors to make the following incisions: cut only through the exoskeleton, which is made of hard chitin to avoid
damaging the soft internal tissues and organs.
 Bend the telson down and make an incision along the joint between the posterior abdominal segments. Cut through the
exoskeleton only. Avoid damaging the soft inner tissues.
 Make the incisions indicated by the dotted lines. Remove the dorsal exoskeleton by slighting lifting it with forceps and
cutting it loose from the soft tissues that cling to it.
F. Second Cuts & Removal
 Some gills were not removed with the walking legs. Remove the fills and the body wall behind them.
 Remove the left ventral wall of the cephalothorax by making an incision from the ventral posterior of the cephalothorax to
just the anterior of the mouth. Cut deep enough to expose the ventral thoracic artery, which runs along the ventral midline.
G. Internal Structures  FIGURE 5
 Identify the structures shown in Figure 5. It will be necessary to remove a portion of the liver, some muscles, and latex
(which leaks from the heart during injection of the circulatory system) to see the heart, gonad (ovary or testis) and sternal
artery.
H. Stomach
 After studying the crayfish’s internal anatomy, remove the stomach, cut through its ventral surface, and spread it open.
Place the stomach in a petri dish and rinse the contents of the stomach into water.
 Examine the water containing the stomach contents under the stereoscope or hand lens.
 What had the crayfish been eating right before it died? How do you know?
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 Examine the stomach interior to locate the three sets of beak-like teeth, which chew the food. Posterior to the teeth are
numerous bristles. These bristles prevent large food particles from passing into the intestine.
 Put the stomach into a petri dish. Examine the teeth under a stereoscope. Draw what you see.
TM :______________
ANALYSIS QUESTIONS
A. Which phyla is the crayfish a part of?
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B. Label the external portions of the crayfish  FIGURE 6
carapace, abdomen, telson, uropods, antennules, antennae, comound eye, cheliped, walking leg (4)
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C. Label the internal portions of the crayfish  FIGURE 7
compound eye, green gland, digestive gland, mandible muscles, gills, abdominal muscles, maxilliped, walking leg
1. ________________________________________________________________________________________________
2. ________________________________________________________________________________________________
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D. What type of circulatory system do crayfish (and all arthropods) have? How do you know?
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E. Match the following structures of the crayfish with their function.
a.
b.
c.
d.
e.
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heart
testes or ovaries
gills
telson
mandibules
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
f.
g.
h.
i.
j.
cephalothorax
antennaw
carapace
swimmerets
green gland
outer exoskeletal covering
organ that regulates salt and water levels (excetory) in blood
body region that includes the head and thorax
movable sensory structures
respiratory organs attached to the walking legs
pumps blood through the open circulatory system
gemete-producing structures located directly beneath the heart
mouth parts that chew and crush food
paired fin on the abdomen that allows rapid backward movement
legs specialized for swimming