Edible Dissectible: The Blue Crab

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1 Edible Dissectible: The Blue Crab Chris Lundberg, Program Coordinator, Mathematics & Science Center Developed with funding from the Mathematics & Science Center Question Background Safety Materials Procedure Can one dissect a crab and eat it too? In this activity, students will learn about the characteristics of a representative arthropod, the blue crab, and then consume and enjoy their lab specimens their edible dissectible! The blue crab, Callinectes sapdius, is the major seafood product of the Chesapeake Bay. They are very good swimmers and are omnivores that feed on a variety of living and non-living animal and plant material. They are classified in the Phylum Arthropoda. They have jointed appendages and specialized senses. They are also called crustaceans. Remember to observe your regular classroom lab safety rules. Make sure that your hands are clean and that your crabs are fresh when you consume your specimen. Specimens of steamed Callinectes sapidus from local seafood company Paper plates Knives and forks Napkins Plenty of newspaper Melted butter or seafood sauce (optional) Follow the procedures below to conduct your dissection of the blue crab. Record your observations in the Lab Data section and then answer the questions in the Questions/Conclusions section. The Blue Crab from Z to A 1

2 Part I. External Anatomy 1. Begin your dissection by observing the external anatomy of your specimen. Examine the basic body shape of the blue crab with its dorsal (back) side up. The crustacean body plan of head, thorax, and abdomen are present, but most of the body is composed of the head and thorax the cephalothorax and covered by a hard shell or carapace. 2. Observe the appendages of the crab. Notice the two chelipeds, or claws. One claw is the cutting claw, and the other is the crushing claw. Examine the remaining 8 walking legs 3. Now examine the head region. Observe the two pairs of antennae that are used to detect sounds and smells. Note that behind the antennae is a pair of stalked, compound eyes. 4. Observe the mouth area. There are 5 pairs of small, jointed appendages that assist in collecting food. The first two pairs are the maxillepeds, the next two pairs are maxillae, and the last pair is the mandibles the jaws of the crab. 5. Observe the apron on the ventral (underside) of your crab. Determine if your crab is male or female. Remember, the apron of males is shaped like the Washington Monument and the female apron is shaped like the Capitol Dome. Part II. Internal Anatomy Now, begin your examination of the internal anatomy of the crab. Note that the internal organs of crabs have little connective tissue and are very delicate. Because of this fact, some organs appear shapeless or without definite structure. You may have some difficulty identifying these internal organs because of this fact especially since these crabs have also undergone some changes due to their cooking! 1. Insert your thumb or the tip of a knife into the tip of the crab s apron. Remove the apron by pulling it back and up. 2. Now, using both hands, pull up and detach the carapace from the rest of the crab s cephalothorax. 3. Examine the internal anatomy of the crab. The epidermis of the crab lies immediately beneath the carapace. The yellow mustard-like fat and the gray, triangular mass of the gills of the crab are easily seen. The solid white masses which make up most of the crab s insides are The Blue Crab from Z to A 2

3 its muscles. 4. Observe the gill bailer. This feather-like structure helps generate current into the gill area to assist the crab in respiration. 5. In a female crab, you should be able to see the orange ovaries. In males, the smaller, white testes are observed. 6. The stomach is a large, transparent, sac lying in the middle of the body and toward the front. Digestive caeca, yellow/greening organs are located. Below the stomach, the soft and gray heart is located. The intestines are difficult to observe, and extend from the stomach to the posterior anus. 7. Remove and crack open one of the claws. Find the large tendon attached to the claw. Use your thumb and forefinger to pull on the tendon see if you can make the claw open and close! Part III. Ingestion of Blue Crab Internal Anatomy Begin this part of your investigation after you have comleted parts I and II and have removed the carapace from the crab s body. 1. Make sure to remove the gills and the fat from the crab s internal anatomy. 2. Break your crab s body in half. Then, break the remaining two parts in half again to expose the spaces containing the delicious solid white crab meat! 3. Now, enjoy the rewards of your scientific research! 4. If you need assistance or further directions for eating your crab, go to the How to Pick and Enjoy a Maryland Blue Crab in the Seafood Section of the following web site: 5. Clean up all of your materials and your workspace. Proceed to answer your questions in the Questions/Conclusions section. The Blue Crab from Z to A 3

4 Lab Data Draw and label a diagram of the blue crab s external anatomy in the space below. Photo: U.S. Govt. FDA Draw and label a diagram of the blue crab s internal anatomy in the space provided below. The Blue Crab from Z to A 4

5 Conclusion / Questions 1. Why is the blue crab classified as a decapod and an arthropod? 2. Are any appendages missing on your crab? Do you see any signs of any limbs regenerating? 3. Why do you think the gills are located in a separate, closed area from the other internal organs of the blue crab? 4. What do you think the reason is for the blue crab to have such large and tasty muscles? What do these muscles help the crab to do? 5. How can you tell a male crab from a female crab? Extensions 1. Go further in your culinary exploration and sampling of this tasty species. Click on for even more recipes for the blue crab. 2. Go further with your investigation of the blue crab s anatomy. Use a light microscope and prepare slides to examine up close the crab s eyes, gill bailers, antennae, and mouth parts. The Blue Crab from Z to A 5