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Biology: Diversity of Protostome Species


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  • Type: Video Tutorial
  • Length: 14:05
  • Media: Video/mp4
  • Use: Watch Online & Download
  • Access Period: Unrestricted
  • Download: MP4 (iPod compatible)
  • Size: 151 MB
  • Posted: 07/01/2009

This lesson is part of the following series:

Biology Course (390 lessons, $198.00)
Biology: The Evolution of Life on Earth (34 lessons, $64.35)
Biology: Invertebrates (3 lessons, $7.92)

Taught by Professor George Wolfe, this lesson was selected from a broader, comprehensive course, Biology. This course and others are available from Thinkwell, Inc. The full course can be found at The full course covers evolution, ecology, inorganic and organic chemistry, cell biology, respiration, molecular genetics, photosynthesis, biotechnology, cell reproduction, Mendelian genetics and mutation, population genetics and mutation, animal systems and homeostasis, evolution of life on earth, and plant systems and homeostasis.

George Wolfe brings 30+ years of teaching and curriculum writing experience to Thinkwell Biology. His teaching career started in Zaire, Africa where he taught Biology, Chemistry, Political Economics, and Physical Education in the Peace Corps. Since then, he's taught in the Western NY region, spending the last 20 years in the Rochester City School District where he is the Director of the Loudoun Academy of Science. Besides his teaching career, Mr. Wolfe has also been an Emmy-winning television host, fielding live questions for the PBS/WXXI production of Homework Hotline as well as writing and performing in "Football Physics" segments for the Buffalo Bills and the Discover Channel. His contributions to education have been extensive, serving on multiple advisory boards including the Cornell Institute of Physics Teachers, the Cornell Institute of Biology Teachers and the Harvard-Smithsonian Center for Astrophysics SportSmarts curriculum project. He has authored several publications including "The Nasonia Project", a lab series built around the genetics and behaviors of a parasitic wasp. He has received numerous awards throughout his teaching career including the NSTA Presidential Excellence Award, The National Association of Biology Teachers Outstanding Biology Teacher Award for New York State, The Shell Award for Outstanding Science Educator, and was recently inducted in the National Teaching Hall of Fame.

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Let's continue to go through the phylogeny of these animals and take a look at our kind of little survey section of our Thinkwell course here and see, as we get further and further along in time, what kinds of things change in these animals. Now, remember what we did. The first thing we did was we said, "Okay, the first group to branch off, those were the parazoans," and they branched off early. I've got to ask you this question. I often ask my students when we enter this section, "What do you guys think is the most advanced animal?" And they say, "People." "Okay, what do you think is the most successful animal?" And they say, "People," and I say, "Why?" and they say, "Because we can kill everything else." Or "We can prey upon everything else. We have intelligence." And I say, "You know, what do you define as success?" If you think of it from a biological perspective, it seems to me success in the animal or any kingdom--but we're talking about animals now--success in any kingdom can be classified longevity. Are you an evolutionary dead end, or have you been around for a couple of million years? Well, yeah, we've been around for a couple our four million years. But sponges--650 more maybe million years. Now, that's the most successful organism.
Now, they may not have intelligence and killer ability, but they're doing okay. But that's not what I want to talk to you about. Today I want to continue going on. So what did we do? We took off those sponges, we took off the parazoa, we took off the radiata, and then we got to the whole idea of coelomates and acoelomates, and so we took off the acoelomates. We took of the pseudocoelomates and now we're into the coelomates. We said, "all right, we're going to take the coelomates up and we're going to break them up into protostomes and deuterostomes," and we're going to continue with the protostomes, because I've got to tell you, I am a protostome fan. I love protostomes. I love to use them for bait and I love to eat them and I like to talk about them, too. They're kind of cool things.
The next group of protostomes I want to talk to you about is a group of protostomes called the mollusks or the mollusca. These guys have done so much evolutionary divergence it's incredible. There are still thousands of species on the planet today, and they've been around for millions of years. What makes something a mollusk? Well, just like everything else, all mollusks have certain things in common. What do they have in common? So if I'm a systematist, here's what I'm looking for in a mollusk. I'm looking for a muscular foot, I'm looking for a soft body, and I'm looking for a mantle. A mantle is a bag that surrounds their guts basically. It's a specialized bag that surrounds their guts. In most of them it makes the shell and forms a cavity called the "mantle cavity." So if you're a mollusk listening to me now, you have a muscular foot, you have a soft body, and you have a mantle, and you're probably the most intelligent mollusk in the history of life.
Let's talk about a prototypical mollusk and what it might look like. We believe that the ancestral mollusk probably looks something like this. It probably had a shell because--here's the thing. What's so special about mollusks? They are and have been very successful, and they became very successful because they came up with this very cool ability, unknown in many of the animals, at least in the invertebrates, and it's the ability to take from sea water, calcium, calcium salts, and put it through that mantle and actually convert it into a shell. They were the first guys--well, I shouldn't say the first ones, because you know, the cnidarians, the corals, could form reefs. But these were the first animals that could internalize this. Now, a bunch of other animals came along later and could do this and make like an internal skeleton out of calcium salts, and that was a great adaptation, but we're not talking about them now. But these guys were able to take that mantle and turn it into a shell. Think of the protection that afforded them. It wasn't much of a shell probably at first, but what protection. And then inside of that thing could live the creature.
So the creature would have its big old muscular foot and its head would extend and its body cavity would be in there. Here's its two antenna. And it would have a mouth, and that mouth would lead into a digestive system, and this whole idea of a coelome and the ability to have guts just allowed these things... I mean, we're even talking about eyes on these. So this was a major evolutionary step.
Now you say, "I've never seen anything that looks like that," but you know what? Just go to the seashore, because there's a creature now--and I want to tell you about the four groups of mollusks because these things are just so cool. I happen to just love marine biology and many of these are marine organisms. The first group of mollusks is a group called the polyplacaphora. Of all of the mollusks, this one resembles the ancestral mollusk in my mind the most, otherwise known as the chitons. Not chitin as in the stuff in bugs--C-H-I-T-O-N--the chiton. The mossy chiton lives along the seashore and what it does is it has this plate, and it lives inside, just like that, and it literally adheres to rocks so strong it's unreal. I've tried to get these things off, and you can't. Now, an octopus can get them off because I have found them eaten on the shoreline when the octopus come out and prowl the tide pools at night.
But as evolution continued and divergence occurred and certain adaptations arrived through mutation, now we came to a group of these things that were pretty tricky, and they were a group called the "gastropods." Now, let me tell you what gastro means. Gastropods means stomach foot. So like the chiton and like the ancestral mollusk, these guys had their stomach in their foot and these would include the snails and slugs. The slugs, it's no big problem. You guys all know what slugs look like. They just kind of look sluggy. They've got their two little antennae, and they've got their eyes in their antenna, and they've got the digestive system, and they're slimy and they live in the woods, and they're nice things. But the snails now--these guys could do something. They came up with a trick--a couple of tricks.
First of all, let's talk about that shell. You could see why nature would select for a bigger shell. The bigger the shell the more likely you ought to be to hide your whole body in there. But you could also see why nature would select against a big shell because it's heavy. So who's going to win? The guys with the big shells or the guys with the little shells? Well, one group came with a spiraling shell, so that the shell wouldn't extend over their body and create a lot of friction and bump along, but the shell would be on top of them like a little house. But wait until you see the dilemma that created. So we've got this shell and so we have this opening and we'd have this snail that could come out of this thing. There's its head. We have a problem with that. How are you going to get this body all the way back in there? And plus, you've got all your other guts and organs and stuff. So they came up with this process, and this process twists the body around during embryology and it's called "torsion." This is great stuff because what a snail does is during its embryology so it can fit within that structure, its body actually twists and forms into almost like something like that so that it can live right within the confines of that shell. This works; snails are very successful.
But I've got to ask you if you'd like to be a snail because there's just one dilemma of being a snail. Snails don't seem to mind it much, but I think you would. Look at its digestive system. See anything about this that you might not like as a snail defecates on its own head? But it's better than defecating in your own house, which is what would happen if their body was shoved up in there. It would get all foul and nasty and look worse than most college dorms.
The next group of mollusks that I want to talk to you about right now are the bivalves. Now, the bivalves--two valves, two shells, in other words. Here's one right here--the clams. Again, open up a clam and what do you find? You find the same organs you find in a snail except now it's not in the foot. The foot is just kind of like a hatchet like extension that can come out. In fact, if you've ever eaten fried clams you're basically eating the clam foot, unless you eat the whole thing. But that whole thing, what we see right here, the body, all the organs are in there, but he has to open in order to take in food because they're filter feeders and the foot extends out. If you've ever eaten scallops, there's a centralized muscle in a scallop, too.
They're cool, but to me the coolest of all came with the cephalopods. The cephalopods did a great thing. Let me tell you what cephalopods mean and then we'll get back to my diagram. Cephalopod means foot head. Cephalo--head; foot--pod. Cephalopod. These guys were swimming snails. They were snails that could swim. How cool was that? So they had their little shells and what would happen with these shells is their foot got modified to a tentacle structure--and there are still some of these around nowadays--that actually was attached to their head and they could swim with jet propulsion. These ruled the seas. You've seen dioramas in museums of the ancient seas. These things were all over the place, and they still exist today. The chambered nautilus is still alive today. But then what happened as it continued--coolest of all--was that they lost their shell on the outside and became what are now known--not like one turned into this, but eventually gave rise to the squids and octopi. And in fact, talk about phylogeny and systematics--squids still have a vestigial shell inside of them. When you cut open a squid--this is the mantle of a squid. When you cut open a squid there's a pen, they call it. It's a clear, plastic looking structure, and that's a vestigial shell. These are mollusks. Octopi have lost that.
One more group and then I've got to let you go. Let's do one more group. If I were to land on this planet and you said to me, "Who rules on this planet?" I'd have to say this group just by sheer diversity of numbers--the arthropods. When these guys first crawled out of the sea, those scorpion-like creatures that came out, the divergence--we went through an age of arthropods that was only replaced by an age of amphibians because some fish got smart and started to jump out and eat these things. Arthropod--think of the adaptations these came long with that mollusks didn't have, that worms didn't have. They had an exoskeleton, a hard outer skeleton joined to muscles inside, and the best thing of all, the ability to move that exoskeleton with jointed legs. They've given rise to very diverse orders, for example, crustaceans. Look at this. Insects, arachnids, the eight-legged ones, and a couple that I don't have--chilopods and diplopods, the centipedes and millipedes. So these things just took off--flies, bugs, everything, arthropods. Definitely the most common organism on the planet, and certainly a well-adapted ones. And those, you guys, are just the protostomes. Wait until we get to the deuterostomes.
The Evolution of Life on Earth
Diversity of Protostome Species Page [1 of 3]

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