Crayfish (Cambarusaffinis) Dissection Lab

Name______Period ______

Crayfish (Cambarus affinis) Dissection Lab

Prelab/Background: Read over the crayfish notes this lab instruction sheet. We only have 1 day to dissect, therefore it is important that you have read and know what to do and what you are looking for. Please answer the following questions using your crayfish notes.

1. List three characteristics that all arthropods share.

2. Name two other animals in the same phylum as a crayfish.

3. The cephalothorax of a crayfish is covered by a thick armor called a carapace. What body regions are fused to make up the cephalothorax?

4. How do crayfish obtain food?

5. What do crayfish eat?

6. Color the external and internal anatomy diagrams of the crayfish at the end Dorsal view of crayfish. of this lab.

7. Give the complete classification of the crayfish. If you do not follow the rules for writing scientific names, you will not receive credit! Domain: Order: Malacostraca Kingdom: Family: Astacidea Phylum: Genus: Class: Species:

Materials: preserved crayfish specimen dissection tray paper towels dissecting pins scissors scalpel dissecting probe goggles forceps latex gloves (optional) lab apron lab sheet metric ruler

Safety:  Please use caution when handling sharp objects.  Wear closed toed shoes, pull hair back if necessary, wear long pants.  Wear a lab apron and goggles.  If you would like to wear latex gloves, you should provide them for yourself, they will not be provided to you. Procedure: External Anatomy 1. Observe the crawfish specimen you have been given and fill out Table 1 below.

Table 1: Crayfish Information Table

Length of crayfish in cm Sex of crayfish # of abdominal segments Length of right cheliped in cm Number of walking legs

2. Observe the external anatomy that you labeled on the coloring diagram in the prelab. Refer to your notes if you need further clarification. Ask for help on anything you can’t find with certainty as you may be responsible for these structures on a quiz or practical.

Internal Anatomy Use your prelab notes and colored diagrams to help you locate the organs.

1. Using forceps, pull out the 2 mandibles and observe. Hint: they feel like little rocks in the mouth of the crawfish. 2. Gently tear off a walking leg (twirl and pull with fingers). Note the segmentation of the leg and the gill at base of leg. 3. Place the specimen in the dissecting tray dorsal side up. 4. Carefully insert the point of the scissors under the top of the carapace (shell) at the back of the cephalothorax and cut up the middle to the rostrum. 5. Cut across the carapace just back behind the eyes and remove the two pieces of the carapace. (set aside on the dissection tray) 6. Note the exposed gills. (Feather-like structures just under the carapace you just removed) 7. Remove the exposed gills and legs attached to the thorax. Carefully separate the dorsal layer of muscles in the thorax and note the light colored heart just underneath. 8. Remove the heart. The two light colored masses extending on each side of the body into the head are the digestive glands. (The heart is located just posterior to these.) 9. Between the digestive glands, you will find the small pair of white reproductive organs in the male animal. If your specimen is female, you will probably see a large mass of dark-colored eggs. (this step may be difficult to observe. Ask your teacher if you are unable to view these structures) 10. To locate the intestine, insert the point of the scissors under the dorsal side of the shell of the abdomen and cut back to the telson. Spread the shell, and the intestine will be found as a tube on the top side of the muscles of the abdomen. 11. Trace the intestine forward to the point where it joins the large, thin-walled stomach in the front part of the cephalothorax. 12. Now, remove all the organs in the thorax by cutting the short esophagus below the stomach and the bands of muscle holding the stomach just back of the eyes. You should be able to lift out most of the internal organs in one piece. 13. Clean out the remaining tissue in the head so that the green glands are exposed. (See photo below for location of green glands) 14. In the front part of the head cavity, between the eyes, note the small mass of white tissue, the brain. (See picture below for location of the brain; there are 2 ganglia joining to the brain in the head region) 15. Spread the shell of the abdomen apart and pull out the large muscle. (This is the part of the body eaten in shrimp and lobsters) 16. Locate the white, stringy connective tissue holding the exoskeleton in place. 17.Use the scalpel to cut the abdominal muscle length-ways and observe.

Clean Up:

With the direction of your teacher, clean up your lab area. 1. Dispose of your specimen in the appropriate place. 2. Place your goggles in the goggle cabinet. 3. Place your lab aprons in the appropriate pile. 4. CLEAN AND DRY your dissecting tools & pan, then place all the dissecting equipment back where it was when you entered the room. 5. NO SOLIDS GO DOWN THE DRAINS!!!! 6. WASH YOUR HANDS BEFORE YOU LEAVE!!!!!!!

Analysis and Conclusion:

1.What similarities & differences did you observe between the internal anatomy of the crayfish and that of a human? (use the names of the organs you observed during the dissection and the names of organs with similar functions in humans; be sure you include all of the major systems; a table may be helpful)

2. Trace the pathway of ingested food through the digestive tract of the crayfish until the waste exits the body.

3. How is the arthropod in this lab similar to arthropods in the group called arachnids? How is it different?

4. How is the arthropod in this lab similar to arthropods in the group called insects? How is it different?