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Name ____________________________________________________________________________________ Date____________________ Period____________ 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? ________________________________________________________________________________________________ What is the relationship between the external skeleton and body size? ________________________________________________________________________________________________ ________________________________________________________________________________________________ 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? ________________________________________________________________________________________________ ________________________________________________________________________________________________ ________________________________________________________________________________________________ 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? ________________________________________________________________________________________________ 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? ________________________________________________________________________________________________ ________________________________________________________________________________________________ What is the advantage of having gills attached to the walking legs? ________________________________________________________________________________________________ ________________________________________________________________________________________________ ________________________________________________________________________________________________ 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? ________________________________________________________________________________________________ ________________________________________________________________________________________________ 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? ________________________________________________________________________________________________ ________________________________________________________________________________________________ ________________________________________________________________________________________________ ________________________________________________________________________________________________ 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? ________________________________________________________________________________________________ B. Label the external portions of the crayfish FIGURE 6 carapace, abdomen, telson, uropods, antennules, antennae, comound eye, cheliped, walking leg (4) 1. ________________________________________________________________________________________________ 2. ________________________________________________________________________________________________ 3. ________________________________________________________________________________________________ 4. ________________________________________________________________________________________________ 5. ________________________________________________________________________________________________ 6. ________________________________________________________________________________________________ 7. ________________________________________________________________________________________________ 8. ________________________________________________________________________________________________ 9. ________________________________________________________________________________________________ 10. ________________________________________________________________________________________________ 11. ________________________________________________________________________________________________ 12. ________________________________________________________________________________________________ 13. ________________________________________________________________________________________________ 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. ________________________________________________________________________________________________ 3. ________________________________________________________________________________________________ 4. ________________________________________________________________________________________________ 5. ________________________________________________________________________________________________ 6. ________________________________________________________________________________________________ 7. ________________________________________________________________________________________________ 8. ________________________________________________________________________________________________ D. What type of circulatory system do crayfish (and all arthropods) have? How do you know? ________________________________________________________________________________________________ ________________________________________________________________________________________________ ________________________________________________________________________________________________ E. Match the following structures of the crayfish with their function. a. b. c. d. e. ____ ____ ____ ____ ____ ____ ____ ____ ____ ____ 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