Blue crab dissection

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As an example of an ARTHROPOD, we will be examining the internal and external anatomy of the Atlantic Blue Crab, species Callinectes. Your crab should look like graphic BLUE CRAB

Follow the instructions in order, and refer to the images cited for assistance in your dissection.

Refer to graphic CRAB55 and your own crab. Answer the following questions:
1. How many "legs" does your crab have?______
2. How many is it supposed to have?______
3. Explain any difference:

Remove all the legs from one side, sketch them below, starting with number 1 at the ORAL end, and deduce the function of each:

Remove one of the large CHELA (claws). Refer to graphic CHELA1 to carefully expose the muscles that operate the claw. Remove the shell as in graphic CHELA2 to see what the opened claw should look like.
Refer to graphic CHELA2, and scrape away the muscle tissue to expose the DORSAL PLATE and the VENTRAL PLATE that the muscles attach to. The DORSAL PLATE is small, and hard to locate.
Graphic CHELA3 shows a photo of the exposed plates.
Gently open and close the claw with your finger, then gently pull on each of the plates in succession. Describe the function of the plates:

Refer to graphic EYE1. Remove one of the stalked eyes, and examine it with a magnifier. The graphic EYE2 is from previous work to help you see what to look for. Sketch the “lenses” of the crab eye:

This eye is similar to insects, with many small lenses with fixed focal lengths. What advantages might this type of lens have over a human eye?

What disadvantages?

Refer to graphic MOUTH1. Examine the small appendages that collect and bring food to the mouth. Remove them from one side only, sketch each one, name the parts, and attempt to determine a function for each:

Examine the DORSAL side of your crab, and sketch the GENITAL PLATE:

Refer to graphics YOUNG FEMALE, ADULT FEMALE, and ADULT MALE. Which do you have?


Refer to graphic CRABINT2 to see how to remove the CARAPACE to expose the internal structures of your crab. The graphic CRABINT shows you a photo of a properly opened crab.

1. Check the underside of the top shell for new shell material. Also, look for developing eggs in the females.
2. The GILLS are in a separate chamber. Why do you think this is so?

3. Observe the demonstration of the circulation of a live crab, if available. How does water enter and leave the gill chambers?

4. Note VENTRAL FLABELLUM (under the gills). What causes them to move, and what is their function?

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