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.