Cancer Borealis Gross Dissection
By Gabrielle Gutierrez for the Marder Lab, Brandeis University
Get a crab from the tank room and place it on ice for ½ an hour.
Take one of the buckets from the lab. I like to put ice in the bottom third before obtaining the crab so that I can place the crab on top of it and then put ice over it. Putting ice both on top of and under the crab will make it less feisty when it’s time to dissect it.
Lay out the tools you will use, put on gloves and roll up your sleeves.
You’ll need rongeurs, big scissors, small scissors, a spatula with a tapered edge, and a pan. Take the crab out of the bucket by spilling out the top layer of ice and grabbing the crab by a hind leg so it doesn’t claw yo’ ass.
Holding the crab with your whole hand, twist off the claws first, then all of the legs. Try to remove each appendage with one swift twist. Try to avoid pulling outward.
Remove part of mouth.
Taking the rongeurs and securing either maxilla, twist it off with one movement. Use the rongeurs to pull out the soft pieces covering the mandibles.
Cut around carapace up to the eyes.
Using the rongeurs again, start from the posterior edge of the carapace and get a good grip on the edge of it. Clamp down with the rongeurs and pull that piece of shell up and off. Make sure that you get enough of the carapace off to allow the spatula to enter.
Push crab tissue away from dorsal carapace.
With the tapered side of the spatula, gently begin separating the tissue away from the dorsal (upper) carapace by scraping the roof of the carapace. Try to keep the spatula in contact with the underside of the carapace at all times to avoid destroying any important stuff under the tissue.
Cut away at carapace.
Little by little, separate tissue from the dorsal carapace and use the rongeurs to remove carapace that has been separated from the tissue. Remove some of the ventral carapace as well to make it easier to get the spatula in at a good angle. Continue doing this on both right and left sides until you’ve removed all of the carapace over the cardiac sac. Cut as far posterior as the heart where there are two protruding ossicles in the carapace and as far anterior as the ridge of the face. Make sure to hold the face of the crab steady when cutting off the carapace that is closest to the face. This part is fragile and you could break off the whole front of the crab, including the parts that you want to keep!
Push more tissue away to clear the way for the cardiac sac.
With the spatula, coarsely separate the tissue from the ventral carapace including any muscles keeping the tissue attached. Also dig out the fatty yellow tissue from the sides of the face up until the eyes.
Pull out mandibles.
Get the rongeurs around a mandible and gently twist it down and laterally to separate the mandible from the ventral carapace. Then put it out like mean dentist pulling a tooth. If you’ve done a good job of pulling it out, two ossicles with muscle will come with it, clearing the way for taking out the cardiac sac.
Carefully cut the tissue across the ridge near face.
This can be done in layers or all at once. Just keep the small scissors parallel to the face without letting the tip of the scissor dig in. Cut as close to the ridge as possible. Once that’s cleared, push the tissue down with the flat edge of the spatula until you can see an arch of ossicle where the lip is attached to the ventral carapace.
Cut the tissue holding the lip to the ossicle.
For this part, rest your crab across a wall of the dissection pan and prop it up with something (like the claws). Taking the small scissors and using the forceps if necessary to hold onto the lip, carefully cut the tissue where the lip meets the ossicle. Make sure that the lip is completely separated from the arch of ossicle.
Make 2 diagonal cuts to take off the face.
Use the two diagonal raises in the ventral carapace as a guide. Don’t cut any tissue and don’t cut anything off that is attached to tissue. The way should be cleared for this part.
Holding lip with forceps carefully cut out the cardiac sac.
First, gently lift the lip up and away from the ventral carapace to cut the tissue right under the mouth. Make clean cuts as close to the ossicle as possible. The CoGs can be damaged here if this fibrous tissue is pulled instead of cut. Once that’s done, move scissors side to side to clear the way to the pylorus by moving that stringy stuff out of the way. The pylorus will look like two brown bulbs. Then cut the cardiac sac out following the edge of it as best you can. There is milky, white tissue around the cardiac sac. This can be used as a guideline to cut where the white stuff ends and the cardiac sac begins. Don’t over-cut. Taking more than you need will hinder your fine dissection.
Still holding prep by the lip, fill the cardiac sac with saline.
The cardiac sac should be resting against the palm of your hand while your fingertips hold the lip by the forceps. Pour Cancer saline into the mouth. I use a squirt bottle to make sure it gets in. This part is just to make it easier to cut open the cardiac sac.
Cut the cardiac sac into a flat prep.
Using the small scissors cut from the mouth down through the pylorus. There is a thin piece of ossicle between the two ampullae. Make sure to cut through that too. Cut along the diagonal white lines toward the bottom. Your prep with now be flat and in a star shape. Cut the tips of the three teeth out.