Introduction: Lobster Dissection
Hooray for lobsters! Giant sea bugs! This is made for biology teachers in a pinch, or aspiring anatomists just coming out of their shell. Lobsters are not only a highly prized seafood, but they're an incredible family of organisms, too. They molt, they can grow back eyes and claws, they don't seem to age, they're everywhere, they're fastest backwards, and they can get up to 40 pounds. For an amazing look into arthropods and marine life, look no further than your friend Pinchy.
- What: Lobster Dissection
- Time: varies, ~30-45 minutes is good
- Lobster (note blow)
- Utility knife
- Gloves (optional)
- Tray (optional)
A NOTE ON DISSECTION:
Dissecting animal organisms is a tricky subject which ultimately some will object to and that's okay. For me, I believe that with careful scientific exploration of animals who were treated in humane ways, we can learn and teach our students to be greater stewards of the environment, and especially toward the species they just learned about. There will always be some students who wish not to do a dissection, and we always allow whatever level of participation they choose in these experiences. Many prefer to just watch. Many of those eventually join in. But whatever it is, feel it out with your classroom or audience.
A NOTE ON LOBSTERS:
An interesting thing about lobsters is that they're often sold live. This means that it is often up to the chef (in normal cases) or the scientist to kill the lobster themselves. Because of this, there has been great debate over the best and most humane ways to do this are. Some argue that lobsters can't feel pain, others say they can. A great synthesis can be found in this article. As a science teacher, I prefer finding ones that have passed away at the grocery store, which are available. If you have to work with a live lobster, packing the lobster in ice several hours before the dissection works to humanely kill the lobster, or you can put it in a tub of ice-cold water and salt slurry as according to the humane society. This is part of what is involved in the cooking process, too, so it is nothing excessive, and is part of eating meat. Lobsters just bring it closer to home.
Okay, lobster time!
Step 1: Claws (Chelipeds)
Starting with the external anatomy, the most striking part of a lobster are the claws (also called Chelipeds). These are the first pair of legs, and different from the rest, because, well, they're giant intimidating claws.
What's neat is the claws develop differently from each other and one becomes the pincher claw and the other the crusher claw. These also seem like great names for members of a metal band. The crusher claw has more girth and has large "teeth" made of calcium that help with breaking shells, and well, crushing. The pincher claw (or cutter claw) is thinner and more docile, made for cutting flesh and striking quickly. Another nifty thing is that if they lose one, they can grow them back the next time they molt.
If you're working with students, you can ask them which they think is which, and you can test their range of motion. Open and close them, and move the whole leg around to see their range and amazing mechanics of their claw joints.
Step 2: Eyes, Antennae, and Mouth
Here's the pretty lobster face that only a mother arthropod could love (or a budding biologist!)
The largest features are the three pairs of antennas, a large pair and two smaller pairs. The large antennas are used for touching, and navigating their way around. Lobsters have poor eyesight, so these function as a good pair of canes for getting around, especially since they often hunt at night. The smaller two pairs of antennas are more flexible and sensitive to chemical signals in the water, such as smelling food. Just above these you'll find the hard rostrum, which though it looks like a nose, serves only to protect the lobster's eyes.
Lobsters have two eyes like us, and do not really see clear images. However, they are very good at sensing dark and light, including shadows in low-light situations. The eye has a reflective layer covering a convex retina, which is super neat. Our retina is concave, like a satellite dish receiving light information from our lens. Their retina is like the outside of a dome, taking light in from all sides. WILD.
Lobster mouths are composed of mandibles (jaw-like parts) and maxipilleds (for bringing food to mouth). If they appear as some nightmare-ish alien death trap, you're not wrong, just perceptive. It's scary in there for small animals, and the scariest part perhaps is that the chomping even continues when you get to the stomach. More on that to come!
Step 3: Legs Legs Legs
Lobsters have legs for days.
Moving from front to back, after the claws we continue with four pairs of walking legs (pereiopods). The first two pairs also have claws on them used for eating, and the back two are pure walkers. This means they can eat with their feet! Neat! You can move these around to see their wide range of motion.
Behind the walkers are the gonopods, which are the easiest way to tell if a lobster is female or male from the outside. In males, gonopods are larger, white, and rigid. They are used for holding on to females during mating, which happens usually right after the female has molted. In females, they are smaller, and used to carry and ventilate eggs.
Behind those are an array of five pairs of swimmerets (pleopods). They look like fins and are used to help with swimming, and move in a beautiful flowing motion if you get to see lobsters in the wild.
Probe each of the legs and articulate them to see their range of motion.
Step 4: The Tail
The abdomen is also known as the lobster tail. It is comprised of six segments, and articulates beautifully. At the back of it, the tail can spread out with parts called uropods and the central telson when needed, and shrink back quickly like a fan. Also, the entire tail can curl up toward the walking legs and uncurl rapidly to help the lobster swim backwards quickly when the lobster needs to flee.
Try articulating both of these motions to test out the leg mechanics.
Step 5: First Cut: the Stomach(s)
Our first cut into the lobster is on the dorsal side on its "back," just behind its eyes. Using a utility knife and a good amount of force, you can cut out a window in the lobster's shell. They're tough!
Remove the plate, and you should be able to see the lobster's two stomachs, the cardiac stomach (closer to eyes), and the pyloric stomach (right after the first). Probe the cardiac stomach, and you can feel something hard within. If you reach in with tweezers, you can pull out its stomach teeth! EEEP! It keeps chewing even in its tummy! You can see these in the photos, but are much stranger to feel in real life.
If you're lucky, you might be able to see the lobster's brain, but it is difficult to find as it is smaller than a pea, and somewhat dark in color. It is just behind the eyes.
Step 6: Second Cut: the Gills
Next up, we're going to use the utility knife to take out a side panel of the lobster's cephalothorax.
Inside, you will be able to see the feathery array of gills. They're beautiful. If you take them out, you can see just how much surface area they have as they are made of many wispy strands packed together. This is optimized for pulling oxygen out of the saltwater it lives in. If you have a microscope, use it for gills. They look incredible.
If you peel back the gills, you can see more a defined exoskeleton (in addition to its shell) that helps give the lobster's insides structure and protection.
Step 7: Third Cut: the Tomalley
Next up, remove more of the top part of the cephalothorax to reveal the tomalley. This is a huge green digestive organ that takes up a large part of the lobster's insides. It fulfills the role of both a liver and a pancreas. It is also called "lobster paste," and is often considered a delicacy. In some places, it can have too high level of toxins to ingest, so check your local FDA listing.
Step 8: The Heart
At the base of the cephalothorax, you will find the heart. It is located right near the dorsal side of the lobster's shell, is a light pinkish, and is amazing. In my case, the lobster had been dead for more than an hour, and the central nervous system disconnected. And still, the heart was still contracting even post-mortem. Look at that first picture. It's actually a GIF.
It's an intense experience, and be quite a moment for a lot of students. It is also a launching point for discussing what the definition of being alive is. If you want, you can have students place their finger on it to feel. Later, when they remove their gloves, you can have them find their own heartbeat as well. I assure you, the lobster is not by traditional means alive even though the heart is still pumping as the nervous system and surrounding ganglion have been detached and inactive for some time.
Often, students will ask about blood, which has actually been all around. Lobster blood is colorless and transparent. It becomes bluish when it comes into contact with oxygen due to the presence of hemocyanin which contains copper.
Step 9: Fourth Cut: the Tail
The next cut is on the dorsal side of the tail, cutting down along the top of it.
When you open the panels up, you can clearly see a white line running the length of the lobster on top of the tomalley. This is the intestine, which will ultimately end up at the anus. Just like us!
Spread across the tomalley in males, you can see two lines which each end with long clear-ish sacs. These are the testes, and the home of sperm production. In females, you can see ovaries, which can appear as a long red line. Sometimes, you can even find lobster roe (lobster eggs).
Step 10: Fifth Cut: the Legs
An amazing feature of lobsters and all arthropods are the way their legs work. They are extremely flexible, and involve an amazing network of of muscles attached to their shell and help from fluid pressure from their hemolymph system. This part is similar to, but not as drastic as the amazing hydraulic leg motion of spiders.
This makes it so that will some pushing and pulling and pressure applied in the right areas, you can make claws open and close with a pair of tweezers. Try it out to see what happens. As you dissect the legs, you will also find translucent stiff parts of the exoskeleton made of chitin, which is found in all arthropod shells. Looking at the claw, you can even find tissue where you can see the site of calcification where new "teeth" of the claw are being formed.
To everyone a claw!
Step 11: Keep Exploring
Hooray! You did it!
And don't let me stop you there, there are more parts of the lobster to be seen. You can look at the inside of the eye or the structure of the lobster's face. Take a look at what the lobster ate, or grab some parts and head to the microscope. There is so much more to learn.
Or to cook! There are a hefty load of recipes and how-to instructions online, and then you can create a no-waste dissection and have participants get a snack, too! This also is great and bringing the human and nature relationship aspect home as well.
I'm excited to see what you learn and find. Feel encouraged to write with comments and questions below!
Have fun, and as always, keep exploring. :)
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