Lophotrochozoans - Online Tutor, Practice Problems & Exam Prep

Lophotrochozoans are a diverse group of invertebrates characterized by bilateral symmetry and protostome development, where the mouth forms first. This superphylum includes trochophores, which are larval forms with cilia for movement and feeding, and lophophorates, which possess a specialized feeding structure called a lophophore. Key examples include mollusks, annelids, and rotifers, each exhibiting unique adaptations such as the radula in mollusks for feeding and the hermaphroditic nature of some annelids. Understanding these organisms enhances knowledge of biodiversity and ecological roles in aquatic and terrestrial environments.

Lophotrochozoans

Okay, everyone. In this lesson on invertebrate organisms, we are going to be specifically talking about Lophotrochozoans. And while they have a really crazy name, I promise they're not that terrible. Lophotrochozoans, that's a superphylum. So, a superphylum is going to be one big group that contains many other phyla. So in this super phylum, we're going to have many different other phyla that we are going to talk about that fall under this category.

Lophotrochozoans have a really crazy name, but it's kind of a smash-up of two of the main types of organisms. As you can see, we have Lophophorates as one of the types of organisms we're going to talk about, and then we have trochophores, another type of organism we're going to talk about. So, Lophotrochozoans is a combination of those two names. Now, these invertebrate organisms are bilateral. Remember, that means that they are mirror images. So, we are bilateral protostomes. Remember they are protostomes. Remember, that means in embryonic development, the mouth is the first cavity that is formed. In contrast to deuterostomes, where the anus is the first cavity that is formed.

Many are coelomates, meaning that they surround their digestive system. This means that they have water inside of their bodies, and they're using that water pressure to keep their bodies upright to give them structure. Like our solid bone skeleton gives us structure, they have a water system inside of their bodies that gives them structure.

Now let's talk about some specific types of Lophotrochozoans. We have the trochophores. These are going to be any types of organisms that have larvae with a ring of cilia around its body, and this is going to be used for swimming and feeding. This is a trochophore larva. Remember that that is the adolescent stage or the non-adult stage of this developing organism. You can see here that I'm highlighting in yellow this ring of cilia, and this ring of cilia is utilized to bring food into the larva and help it move around. Remember whenever we learned about cilia, these are going to be projections from the cells and they do have movement.

Some examples of organisms that are trochophores are going to be mollusks and annelids. We're not going to talk about mollusks or annelids in this particular lesson, but coming up in the next couple of lessons, we will definitely talk about mollusks and annelids. So, mollusks are going to be things like oysters and clams and scallops, and annelids are actually segmented worms like earthworms. And they are trochophores because they have larvae with a cilia ring.

Now let's move on to the lophophorates. This is a different type of organism. These are going to be animals with a lophophore. A lophophore is going to be a really specialized feeding mechanism, so a specialized structure used for suspension feeding. You can see that it looks like a little crown of these little cilia or these movable projections. Commonly, you'll see this structure called a crown because it kind of sits on the organism and it'll move its little fingers and grab food from the water that surrounds it. This is going to be a lophophore, and it is a really interesting feeding mechanism that grabs food and then pushes it towards the mouth of the organism.

Some examples of Lophophores are going to be ectoprocts and brachiopods. Ectoprocts are actually what you are looking at here. These are going to be coral reef-building animals, but they're not coral. We will talk about coral in a bit. Coral is actually a cnidarian, not an ectoproct. Ectoprocts do create coral reef structures. They actually kind of look like moss. So if you can see here that it kind of looks like a hairy little structure that might look like a patch of moss if you saw a whole bunch of these organisms together. And they look so much like moss that another name for ectoprocts is going to be Bryozoans. And if you remember or if you've gone over the lesson on plants, the name for moss is bryophytes. So, these are bryozoans. They look like moss. Those are two names for the same thing. Ectoprocts and bryozoans, they're the same thing, but they do look a lot like moss, and some of them do have these hard exoskeletons that allow them to build these reef-like structures. They look like mollusks. They kinda look like bivalves, but they're not. They're not bivalves even though they look a lot like bivalves.

Brachiopods, their name actually means "arm foot." And their arm foot, you can see right here, is utilized to hold them in place, to give thema place to hold on to. They use this arm foot to actually dig into the sand or the dirt and hold themselves in place. They're mostly marine animals, but they're not bivalves. Even though they do have two shells that close, they're actually not bivalves. Bivalves will have a left and a right shell and commonly open their shells like this. However, brachiopods have a bottom and a top shell, and they commonly open their shells like this, and the foot will stick out the back. So that is what a brachiopod is, which can be confusing with bivalves. But these are Lophotrochozoans.

Okay, everyone. So now we're going to talk about more invertebrate organisms, and we're going to move on to mollusks. Okay, everyone. Let's go into our next topic.

Mollusks

Mollusks are kind of the star of the show for the lophotrochozoans. And that's because they come in a wide variety of classes that have a bunch of different morphological features that are quite diverse. Now, mollusks, as a whole, are coelomates, and their bodies tend to have these three characteristic pieces, what we call the foot, which is basically a large muscle. Usually, it's going to be used for movement. We'll see a pretty interesting exception with creatures like squid. So anyway, this bottom piece right here in our example, that is going to be the foot.

We also have the visceral mass, which basically includes the internal organs of the organism and its external gills. And that's all this mess here. This is our visceral mass. I'm just going to write vm for visceral mass. And the cavity inside of this is called the hemocoel, and it's named for the fluid inside of it called hemolymph, which is similar to blood, basically. So, the hemocoel, that's the cavity, and it's filled with that fluid that is going to act similarly to blood, and that fluid is actually going to directly bathe the organs because these organisms mostly, there's going to be an exception we'll talk about later, have an open circulatory system. So, the fluids that are going to carry gases to the organs are not going to move through veins or arteries or anything like that. It's just kind of floating around in the hemocoel.

The feeding structure, briefly, I want to mention, as part of the visceral mass, is called the radula. It's at the anterior end, what you could, I guess, kind of think of, like the head. And it's a little hard to see in this image, but the radula is right there. And basically, this feeding structure, it functions kind of like a rasp. So, you know, think about an abrasive edge or abrasive surface kind of rubbing on the food to break it down, like, in a grinding type way. Now, not all mollusks have a radula, but many of them do, so that's why I mention it here as sort of a general feature of mollusks.

The last structure that's common to mollusks is the mantle, and this is basically just a covering for the visceral mass. So, you can see that it's actually this layer here. This layer just under that outer shell in the picture, that is a mantle. And it often forms a hardened calcium carbonate shell, which we can see right here, this is the shell. But this is not always the case, so again, we'll see some exceptions. So, it's worth noting that in some species there's something called a mantle cavity. And it's basically a water-filled chamber containing the gills and the anus. And you can see that little mantle cavity right there.

Now, I'm going to talk about a bunch of different classes of mollusks, and the first one, not a ton to say about. These guys are called chitons. They totally look like some type of prehistoric organism. And what defines them is that they have a shell, which you can see on the top right here, this is the shell. And the shell is made up of 8 dorsal plates. You can see there's like 8 segments to this shell. You can also kind of see the foot poking out from underneath this chiton.

Now, gastropods, probably an organism you're much more familiar with, these are slugs and snails. They're going to live both in marine and terrestrial environments. And while many of them have shells, not all do. Of course, our snail, pictured right here, has a shell, but, you know, there's plenty of these organisms, these gastropods, that don't have shells. Now, many of these species actually reproduce through sexual reproduction. If you ever want to see a wild YouTube video, look up something like slug reproduction. Pretty crazy acrobatic act. Some species, however, perform parthenogenesis, which is that type of asexual reproduction we discussed previously. With that, let's turn the page.

Annelids

Bivalves are arguably the most delicious mollusks. Though, I think it's up for debate with cephalopods. Now, all species of bivalves are aquatic and contain their body within 2 shells. These are organisms like clams, mussels, oysters, which you can see right here, and, a very important feature of oyster anatomy is lemon and of course, inside here, mignonette sauce. Very important for oysters. Of course, I'm kidding here. However, when you look at that sort of meaty body inside the shell, what you're looking at is both the foot and the visceral mass. And the shell itself is, kind of, acting as the mantle here. So, you know, it looks different from the picture we saw on the previous page when we discussed the anatomy, but all those parts are still here. Now, most bivalves are suspension feeders and they lack that radula, that rasp-like eating apparatus. Instead, they, you know, move water through their bodies and pick up on little particles of food that are suspended in the water, and they trap this food in their gills. And you can see these tubes coming out of these clams over here, and those are the structures that they're using to feed.

Now, cephalopods, as I said, are also in the running for most delicious mollusk. Really hard to say. Yeah. Real this is really difficult. It's such a toss-up. I mean, calamari here, really important cephalopod. I don't know what we would do without squid. Most cephalopods are marine predators that have a foot that basically evolved into tentacles. That's what I was referring to earlier when I said, you know, see an example of the foot taking really interesting morphology. Well, it's tentacles on these cephalopods. And these are, you know, organisms like squid, like this nautilus here. And these guys move in a really cool way. They use this structure called a siphon, which is this muscular tube, right there, to eject water. And this actually allows them to travel through what is technically jet propulsion, believe it or not. So these are nature's jets, basically. Now, they're the only mollusks to have a closed circulatory system, and cephalopods, in general, are pretty advanced organisms. They actually have sophisticated nervous systems and pretty complex brains. They also have some pretty cool sensory organs and a variety of other adaptations. You know, a great example is cuttlefish, which are able to camouflage themselves. They have a very sophisticated nervous system. There are also some pretty famous and funny examples of octopi tricking researchers studying them, proving that these animals actually have some pretty sophisticated cognition.

Now, unfortunately, the last type of creature I want to discuss is kind of yucky and is not a mollusk. It's pretty important to note. Annelids are not a type of mollusk. They're their own phyla, And, they are coelomates, most are segmented worms, and they both live in aquatic environments and in damp soil. And we're going to see 2, sort of, basic kinds of annelids. They're these polychaeta, which have parapodia. And you can see all these little parapodia here as little, you know, leg-like structures along the worm body coming out of the segments of the worm. And these parapodia have what are called chaetae, which are basically these chitinous bristles that the worms use to propel themselves through the water. And if you look, you can see there are, sort of these, like, light projections sticking out of the tips of the parapodia. Those are the chaetae. Those are the bristles that the worm uses to, you know, almost swim, you can think of it as. So the other type of worm is going to be, stuff that you're probably a little more familiar with. These are organisms like earthworms and leeches. They're, they're called clitellata, and these organisms are hermaphrodites, meaning they can reproduce sexually. And the organism has both the male and the female parts. Although, some species will actually reproduce asexually. That's the end of this video. I'll see you guys.

Here’s what students ask on this topic:

What are Lophotrochozoans and what are their key characteristics?

Lophotrochozoans are a superphylum of invertebrates that include diverse organisms such as mollusks, annelids, and rotifers. They exhibit bilateral symmetry, meaning their body can be divided into mirror-image halves. They are primarily protostomes, which means during embryonic development, the mouth forms before the anus. Many Lophotrochozoans are coelomates, possessing a body cavity called a coelom that surrounds their digestive tract. Key features include trochophore larvae, which have a ring of cilia used for movement and feeding, and lophophores, specialized structures for suspension feeding. These adaptations help them thrive in various environments.

What is the difference between trochophores and lophophores?

Trochophores and lophophores are two distinct types of organisms within the Lophotrochozoan superphylum. Trochophores are characterized by their larval stage, which features a ring of cilia around the body used for swimming and feeding. Examples include mollusks and annelids. Lophophores, on the other hand, possess a specialized feeding structure called a lophophore, which is used for suspension feeding. This structure resembles a crown of cilia that captures food particles from the water. Examples of lophophorates include ectoprocts and brachiopods.

What are the main classes of mollusks and their unique features?

Mollusks are divided into several classes, each with unique features. Gastropods, such as snails and slugs, have a muscular foot for movement and often a coiled shell. Bivalves, including clams, mussels, and oysters, have two shells and are suspension feeders. Cephalopods, like squids and octopuses, are marine predators with tentacles evolved from the foot and a closed circulatory system. Chitons have a shell composed of eight dorsal plates. Each class exhibits adaptations that allow them to thrive in their respective environments.

How do rotifers reproduce through parthenogenesis?

Rotifers reproduce through a process called parthenogenesis, a form of asexual reproduction. In parthenogenesis, females produce unfertilized eggs that develop into more females, essentially creating clones of themselves. This method allows for rapid population growth without the need for males. Rotifers are microscopic organisms that play a crucial role in freshwater ecosystems, serving as a major food source for various aquatic animals.

What are the differences between flatworms and annelids?

Flatworms (Platyhelminthes) and annelids are both invertebrates but differ significantly. Flatworms are acoelomates, meaning they lack a body cavity, and have a rudimentary digestive system with only one opening. They rely on diffusion for gas exchange and waste elimination. Annelids, on the other hand, are coelomates with a segmented body and a more complex digestive system with separate mouth and anus. They have a closed circulatory system and often possess structures like parapodia and chaetae for movement. Examples of annelids include earthworms and leeches.