Today we're going to be doing a lamprey dissection and a lamprey is a jawless fish. You can see if we take a look at this jaw right here, it's circular. It doesn't have the joint on either side like you do.
It does not have... have a movable jaw that can actually open wide and then close. So it's got a circular muscle around here and what the lamprey actually does is it comes up next to a fish which is its prey and it basically clamps on and grips on using its circular muscle and then using its horned teeth inside here it drills a hole through the side of the fish and actually sucks the blood out. So it's a parasitic animal and that's its nutrition is the fish's blood.
Now before we go on any further let's go ahead and talk about anatomical locations. So this is going to be the mouth. So this is going to be the anterior aspect. of the lamprey. If we go down to the other end, this is going to be the posterior aspect.
The back of the fish, which is where the fins are located, is going to be the dorsal aspect. That's why these fins are going to be called dorsal fins. And opposite that, on the belly side, that's going to be the ventral aspect.
aspect. So let's go ahead and we're going to roll our lamprey back so it's right side up again and let's go ahead and start with the headward region. We're going to start by looking at these two opacities.
Here's one right here. And here is another opacity right there. Those are the eyes.
And the reason they're not transparent is because the preservative denatures the tissues. And it makes that lens or that eye cloudy. So those are the eyes. Right between the two eyes, we're going to see a little hole.
There's right between. If we go just anterior a little bit, there is a tiny hole right here. And that hole. hole is the olfac-that hole is the external nostril. And that external nostril leads to an olfactory bulb which is used to process the sense of smell.
So that's how the lamp ray actually smells. Now, if we look at this area right here, let me go ahead and hold it like this, we can see that there's some additional holes right here. And in fact if we count them, one, two, three, four, five, six, seven, eight, nine, ten, eleven, twelve, four, five, six, and seven. These holes are referred to as external gills. That's where the water is actually going to enter the lamprey, and that's where gas exchange is going to occur inside there.
So these are external gills, and we have those same external gills on the other side also. If we go back to the eye region again, If we look around here, we're going to see some tiny, some very tiny, you can actually feel them with your glove, but there's some very tiny little bumps, almost like pimples here. And we also have some, let's see, I can see them right down.
through here and I can see them right along here. These little tiny bumps make up the lateral line system and that lateral line system is used to detect vibrations in water. A lot of scientists feel that our tympanic membrane, our ear, is actually related to the lateral line system. However, the lateral line system is much more elaborate.
Again, it's used to detect vibration. The next thing I want to do is go more posterior, and I'm going to flip it over so that we're looking at the dorsal side of the lamprey. You can see that the lamprey only has a single fin on its back. back.
It doesn't have paired fins. And that's one of the reasons why the lamprey kind of moves like a snake through the water. Because it doesn't have paired fins, it doesn't have the steering, the maneuverability, and the balance that a fish with paired fins would have.
So paired fins is an evolutionary step forward. But our lamprey has a single fin down its back. And the fin can actually be divided. We have an anterior and a posterior.
And because they're on the dorsal side, we're going to call this the anterior dorsal fin and the posterior dorsal fin. And these dorsal fins are actually used to keep the lamprey upright. Without this dorsal fin, the lamprey would literally tip one way or tip the other way. Now, if we take a look at the posterior dorsal We go ventral.
I'm going to go ventral. Flip this guy over. We see a hole and there's actually two holes there.
Right here is one hole. This is going to be the anus. That's where the digestive tract ends. And then there's going to be another small hole just posterior to it back here.
This common opening back here, this posterior hole, is going to be called the cloaca. And that is a colloidal. opening where the reproductive tract and the urinary tract kind of come together that's where excretory and it's where your metabolic waste leave it's also where your eggs or your sperm leave whatever the case may be so again that's going to be called the cloaca the last thing I want to talk about in terms of external anatomy is this right here we can see that this section right here that's going going to be called the caudal fin. And that caudal fin is what actually propels the lamp ray forward. It's this caudal fin that is used for propulsion and moves the lamp ray forward.
At this point, after you go through the external anatomy, it's time to actually cut the lamp ray in half. So we're going to literally cut the lamp ray midline, all the way down. So what I first want you to do is take the lamprey and you're going to take your scalpel. Now when you have the scalpel we want a nice firm grip on the scalpel so I'm actually going to put it so that the handle is in my hand like this. I'm then going to grab onto it and I'm going to take the scalpel and make sure my hand is behind the scalpel and I'm going to put the scalpel straight through the lamprey until it touches the mat.
And then once I do that, I'm not going to do it on this lamprey. but you would put it all the way through the lamp bracelet so that the scalpel literally touches the mat. And then very slowly you're going to move the scalpel forward, cutting midline, right down the center. You actually want to go right through the external nostril and right through the mouth. Once you do that, go ahead and gently turn the lamprey around.
Again, have your hand behind the scalpel. And you're going to start where you left off. And you're going to continue to cut midline all the way down.
And when you get to the dorsal fins, go ahead and cut right through the fin as midline as you can. Keep going, going, going, going until the very end. And at that point, you should have two, your lamprey should be cut in half. half.
Now at this point I'm going to go ahead and I'm going to take my previously bisected lamprey and I'm going to put it here. So there we go. That's what your lamprey should look like if you cut it midline and it is important to cut it midline. So let's go ahead and start with the mouth.
So this right here is called the buccal cavity and buccal means mouth or cheek. So this is going to be called the buccal cavity. We can see these horned teeth in there. They're very sharp and they're used for actually boring a hole through the side of the fish. Around the mouth we see this sort of fluffy material right around here.
This is called the buccal papilla. The buccal papilla or papillae. And they are actually sometimes referred to as the sensory papillae because they actually sense touch.
And they allow the lamp rates actually feel what it's in contact with. You can also see in cross-section, you can see the muscle here and the muscle here. That's the buckle muscle that is actually used.
That actually tightens down and attaches to the lamp. to the fish. Once the food, once the blood enters the buccal cavity, it's going to go up and over the tongue.
So this structure right here is the tongue. And again, it's also a fierce structure. You can see, again, it has horned teeth on it. So the food is going to go past the tongue and it's going to go down this tube called the pharynx. So this is the pharynx right here.
Now once it goes down the pharynx, the pharynx is going The pharynx then branches into a dorsal branch, which is back here, and a ventral branch, which is right here. So this is your dorsal branch. This is your ventral branch.
Let's go ahead and start with the dorsal branch. So this is going to be the dorsal branch. It's eventually going to give rise to this structure right here that the probe is in.
That's going to be the esophagus. And then... And that esophagus is going to...
Continue until about this point, until right around the heart. At this point, it's going to become the intestine. And you can see this tube I have elevated right here. This tube actually goes between this green organ called the liver.
and this other structure right here. This structure right here is all referred to as the gonad. And we can see that the intestine kind of dives between both of them. I'll put the testine back to where it would have been located, which would have been right in here. And you can see the hole there, that's the intestine.
Again we're going to pick up the intestine here. If we follow it further we can still see the intestine. You can see it continue all the way down until finally right here, if we remember, that's where the anus was. That's where the intestine is going to enter right here.
That's where your digestive waste leaves. That's called the anus. the anus. Now let's go back here again.
So we've got the pharynx, which then branches into a dorsal branch, which becomes the esophagus and eventually the intestine, and a ventral branch. So this ventral branch right here becomes the respiratory. tube.
And that respiratory tube gives rise to this structure right here. These are gills. We can see how they're kind of light and fluffy right here. You can see if you look closely, you can actually see lots of gill filaments. So there's a lot of surface area there.
I'm actually going to show the other side. Here's the other half of the lamprey. And here we can even see better. You can see all the gills.
You can see the striations in the gills that make up the gill filaments. These are all gills right here. Lots of surface area for gas exchange. Now if we go back to this again, this whole thing, these are all gills, we can see an opening right here. This opening is the internal gill slit.
And if we follow that, I can actually put the probe in there, and if I follow that through, it's actually going to come out the back right there in an external gill slit. So water is going to come in the external gill slit and it's going to come in and it's going to go into those gills and eventually it'll get to the internal internal gill slit right there. So these are all gills, and that's an internal gill slit.
Posterior to that is gonna be this structure, and I'll try to lift it up just a little bit there. You can see it's a very muscular structure, and that is the heart. That is the lamprey's heart right there. All this is gonna be the heart. And then posterior to that, we have this green organ which is the liver again superior I shouldn't say soup but dorsally you can see the intestine again now let's go back and again we'll start at the headward region anterior and this is the nostril the external nostril right here it comes in and that external nostril ultimately ends in this black structure here This black structure is going to be the olfactory bulb or olfactory sac And that is actually going to sense and process the information and allow the lamprey to smell If we go just posterior to that right here, we can see the brain So this whole structure right here is the brain And then an extension of the brain or a continuation of the brain all the way down through here Is going to be the spinal cord Now remember, in the larva, the immature form, this is going to be the dorsal hollow nerve cord.
And as the lamprey matures, that dorsal hollow nerve cord gives rise to the brain and the spinal cord. Take a look at this structure right here. You can see this structure go all the way down. It goes all the way down the entire length of the lamprey.
This structure right here is the notochord. This notochord is responsible for flexible support. It's like a flexible rod. And notochord, you can hear the word cord in there, and that's what chordates are named after. So the lamprey belongs to the phylum chordata, or chordate.
And that's what we're actually named after, is this notochord. And again, just dorsal to the notochord would be where the dorsal... hollow nerve cord is that becomes the brain and the spinal cord.
Let's see, what else do we have left? We can see a little bit of cartilage right here. If we take a look at this, you can feel that with your probe. There's some cartilage here.
So not only does the nodal cord give support to the lamp ray, but also this cartilage also provides support to the lamp ray. And that's going to be it for the lamprey dissection.