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Animals, Part I

Lecture Slides are screen-captured images of important points in the lecture. Students can download and print out these lecture slide images to do practice problems as well as take notes while watching the lecture.

  • Intro 0:00
  • Animal Basics 0:05
    • Multicellular Eukaryotes
    • Motility
    • Heterotrophic
    • Sexual Reproduction
    • Symmetry
    • Gut
    • Cephalization
    • Segmentation
    • Sensory Organs
  • Reproductive Strategies 3:07
    • Gonads
    • Fertilization
    • Asexual
  • Animal Development 7:27
    • Zygote
    • Blastula
    • Gastrula
    • Embryo
  • Symmetry 13:17
    • Radial Symmetry
    • Bilateral Symmetry
    • Asymmetry
  • Body Cavities 17:22
    • Coelom
    • Acoelomates
    • Pseudocoelomates
    • Coelomates
  • Major Animal Phyla 20:47
    • Phylum Porifera
    • Phylum Cnidaria
    • Phylum Platyhelmininthes, Nematoda, and Annelida
    • Phylum Rotifera
    • Phylum Mollusca
    • Phylum Arthropoda
    • Phylum Echinodermata
    • Phylum Chordata
  • Phylum Porifera 25:15
    • Sponges
    • Oceanic or Aquatic
    • Adults are Sessile
    • Structure
    • Sexual or Asexual Reproduction
  • Phylum Cnidaria 28:49
    • Sea Jellies, Anemonse, Hydrozoans, and Corals
    • Mostly Oceanic
    • Body Types
    • Cnidocytes
    • Nerve Net

Transcription: Animals, Part I

Hi, welcome back to, this is the lesson on animals, part 1.0000

Some animal basics, if we look at kingdom animalia as a whole, what is typical of these organisms?0007

Like plants and fungi, they are multicellular eukaryotes.0013

Each one of cells has organelles that have membranes, nucleus, mitochondria, golgi, lysosomes, etc.0017

Motility, they typically move themselves.0027

You will see there are some examples of animals that do not move themselves as adults, but that is rare.0031

The vast majority of animals, they move as adults, they move as little babies, this little larvae forms, 0037

and that is how they get around, that is how they get food.0043

Heterotrophic, speaking of food, they eat.0046

They do not make their own food, they have to get their food from outside themselves.0049

And that source of organic nutrients, varies depending on the animal.0053

Sexually production, that is a very common in the animal kingdom.0057

A male and female version, combining their DNA through the process of meiosis and0060

making little gametes that is fused together with fertilization.0065

There are some that do asexual, that is not as abundant in the animal kingdom as sexual production.0069

Symmetry, usually there are some kind of body symmetry like you could divide their body in half,0074

and see two different sides, or their body is more circular.0079

I will tell about those types symmetry in a little bit.0083

They have a gut, some kind of area where they take food in, break food down, and get rid of waste.0086

Sometimes, there is one gut opening, sometimes there is two.0094

We have two, in and out, of course.0097

Cephalization, having a head with a brain inside of it and sensory organs that are able to see, hear, smell, whatever.0100

That is cephalization, the process of making a head with a brain.0110

Segmentation, usually they are body segments, for instance a head, a mid region and bottom region, abdomen, and some of them.0114

Depending in the animal, the segmentation varies.0122

Sometimes, they have very repetitive segments throughout the body, like an earthworm, for instance.0124

Sensory organs, not all of them have well develop sensory organs but 0129

it is very common for animals to at least be able to sense light and react to light.0133

Others can see like us, shapes and colors, and hear variety of noises, and taste, and smell, etc.0138

I have a variety of animals here in the picture, you have got a cnidaria, a sea anemone with its little mouth there.0146

It uses its stinging tentacles to grasp prey and bring into its gut.0153

You can see barely here and here, a sea star or starfish.0158

This is actually from a different phylum, the venomous called the echinoderms.0162

It has its mouth on the underside and its anus on the top.0165

This actually has an opening with two to its gut, in and out, this has a one gut opening.0170

Here, you got a bird eating an earthworm.0180

Animals eat right, that earthworm is just eating before it got picked off.0182

Reproductive strategies, how do they make more animals?0188

Animals reproduce sexually, that is typical, there are some exceptions to that.0192

With the sexual reproduction, you have these organs called gonads.0198

They are the organs that produce sperm or egg.0201

Usually, the sperm producing, what is called a testis or a testicle.0204

The egg producing one would be called an ovary.0209

Hermaphrodites will have both kinds, they can produce both sperm and egg.0212

Some animals definitely fall in to that category of hermaphrodity, they can mate with any individual.0216

The majority of them cannot self fertilize because of the organization of the gonads in their body, 0223

they cannot send sperm to the other part.0228

The advantage, like with an earthworm species, they are all hermaphroditic.0230

They can mate with any other earthworm, they do not have to specifically find the other sex, anyone will do.0235

Fertilization, in terms of actually getting those gametes to fuse together, that sperm and egg, 0241

it can happen externally, meaning, the male and the female release sperm and egg into the water.0247

And the reason why I say water is, that is usually where you see external fertilization.0254

Sperm. For them to travel, need an aqueous environment, some kind of fluid to get them moving to where the eggs are.0259

Usually, aquatic organisms, is where you see external fertilization.0266

There are some animals in water that still do it internally, you will see examples of those later.0271

But it is very rare to find external fertilization on land.0276

Usually with land animals, you are going to see internal fertilization where they have to make contact.0280

The male will inject the sperm into the females body, where they will fertilize the egg, and that is internal.0286

Asexual occurs with some, like I said, asexual reproduction, here are some examples.0294

Budding, with budding you can actually have this with sea anemones, quite often.0300

They will bud off like meaning, they can just actually have a little piece of them pinched off and become a separate anemone.0305

It is like cloning themselves, essentially.0312

That is what yeasts do and this is what can happen with some simpler animals.0314

Fragmentation, meaning some animals, if you cut a part of them off, they will grow into another one.0319

An example of that is the hydra, a hydra, you will see a picture of them later on this lesson.0329

They are named hydra because of the mythical hydra from Greek mythology.0335

It was a dragon that have many heads.0340

We would cut them off, they would regrow.0342

If you cut a hydra in half, it will make more hydra.0344

It can actually, with fragmentation, can make a new one.0351

Regeneration is similar, meaning if I cut one of these off, it will regrow its local tentacle.0355

You could see this with other animals like a planarian, a very simple kind of worm, a flat worm.0363

It has little eye spots there, and it is very flat and small.0370

If you cut it in half, it will make two new halves.0373

One side will make the new head end, one side will make the new tail end.0377

They are simple enough to do that.0380

A lot of other animals, you cut them in a half, they are dead.0382

Parthenogenesis is when a female can self fertilize.0385

It is common with a lot of invertebrates, with vertebrates, animals that have a spine, you will not see it.0391

You will not see it in birds and mammals, it has not been observed in birds and mammals.0405

I have heard about it with alligators, crocodiles, a female will be isolated for a long period of time0415

and she will give birth, she will eggs fused inside of her, and lay eggs, lay offspring.0422

It is happening in some amphibians, frogs, for instance, it has happened in fish.0428

But with birds and mammals, maybe it is something about more complicated reproductive factors.0434

I am not sure but has not been observing those.0439

Parthenogenesis, beyond vertebrates, it can be observed as well.0442

Animal development, after fertilization, when you have sperm and egg combining, you get a zygote.0448

This is the first cell of life, and that results from fertilization.0454

When that is just going to mitosis, you can see it here, look there is a zygote, two cells to four cells, etc.0461

Eventually, you will get a hollow ball of cells that is fluid filled.0470

I’m calling it hollow because there is no cell in the center.0484

It is just like bordering of spherical cell ball.0488

The cool thing is, with the average zygote, there is one giant cell, 0494

combination of sperm going in there and combining its DNA with the eggs DNA.0500

But here, we see like a blastula, that hollow ball of cells.0504

Notice that the size of this, they made this purposefully like that.0510

The size of the blastula is nothing much bigger than the zygote.0513

In terms of cell division, you take that amount of cytoplasm that was in the original zygote, and it gets divvied up.0517

It gets divided up amongst a lot of cells.0524

It is the cells that get smaller and smaller as mitosis ends up making the blastula.0526

Once gastrulation occurs, this folding part, you will get certain cells getting bigger depending on what cell type they are.0532

The thing will actually expand in size.0543

Gastrulation, a gastrula occurs when the blastula undergoes folding,0547

meaning there is this in folding that happens right here, you can see it occurring and that ends up making layers.0553

The ectoderm is the outer layer of cells, the endoderm is this inner layer.0562

There is an initial hole here, it is called a blastocoel that occurs in here, and this is a blastopore.0577

This initial hole, I will tell you a little bit later about how it is either going to become the anus or the mouth, depending on the organism.0586

This, early on, when it is just this ball of cells with the folding in, you already have some determination, 0594

in terms of like directionality with the digestive tract, which is pretty amazing.0600

If there are only two layers of cells, this is typically with the simpler animal groups,0606

not as well developed, in terms of their body.0612

They are diploblastic, that means two layers that developed from the folding in of the blastula.0616

Here is diploblastic, but others, like our selves, are triploblastic.0622

Here is what I mean, here is that outer rim of cells, here is the inner endoderm.0628

And then, we have a layer called the mesoderm which ends up pinching out, to form this inner middle layer of cells.0642

We can trace the development of the majority of our major organs from these different areas.0655

For instance, a lot of parts of your skin and nerves system arise from this outer layer.0660

A lot of your digestive tract, the major parts of your alimentary canal, come from the green area.0667

Which make sense, the digestive parts are like the most inner parts of us.0674

You know, once it goes to the mouth, goes deep inside of you, until eventually exits.0679

Your alimentary canal, known as the digestive tract arises from this endoderm.0683

Mesoderm forms other parts in the middle, glands, and muscles, etc.0687

There is a lot of interesting studies that have been done from, in terms of tagging cells with some indicator.0693

We see that if we tag the mesoderm, what tissues in this little embryo0704

end up having that same fluorescence, or that same tagging?0709

We could see where they have arisen from.0713

We are triploblastic because of that mesoderm.0716

Protostome versus deuterostome.0719

Protostomes, that first hole, that blastopore, the first hole is the mouth.0722

The majority of the animal groups that is true, worms, insects, mollusks, their first hole is the mouth.0737

Later on, the anus develops.0745

Deuterostomes, that is us, and echinoderms, the group that would call sea stars or starfish, and sea urchins and sea cucumbers.0747

They do not look that much like us but we have that in common.0757

There are some theories that we are actually more related to them than we might think.0760

Appearances can be deceiving.0767

The first hole in our development, as just the ball of cells ends up turning to our exit hole for our waste.0769

After gastrulation and the formation of a head end, you know the sides of the body becoming clear, we finally get an embryo.0777

And then depending on the organism, we can then call it a fetus, and then eventually a baby.0785

Depending on the organism, the baby has different names, chick, whatever it might be.0793

Symmetry, animals usually have symmetry in their body plan.0799

You know, its shapes, if it is symmetrical dividing it in half, two sides that are exactly the same.0806

It is not always quite that simple.0813

There are different kinds of symmetry that exists in the animal kingdom.0816

I will give you the three major ones, one of them is the lack of symmetry.0819

But the reason why it pertains to a kind of movement is, if you imagine the way like a sea jelly moves,0823

it does not have a true right and left.0828

It does not really have a head, it just does this.0832

A lot of the animals that have real symmetry, the way they behave, in terms of how they move,0835

there are some similarities there.0841

When organisms has a head end, a true right, true left, a true top, a true bottom,0843

there is some differences there, in terms of how they move and how they orient themselves.0848

Radial symmetry, if we look at the top of this, here is the top like looking down on it.0854

If we divide it in half, those sides look the same.0862

But guess what, if we divide it there, those sides are not the same.0865

If we keep dividing it, this is radial symmetry.0868

You could see it by doing this, I have form a bunch of radii.0874

But, if you think about kind of how it is oriented, as kind of a circular body shape, that is radial symmetry.0887

It is the same with the sea star, in terms of how its body is just this repetitive extensions coming out from the center,0896

you could say that the sea star has a radial symmetry.0906

A sea urchin which is related to see stars, it just has these little spines coming off of it.0909

It can articulate like little hard arms, that also haves radial symmetry.0915

That is how you can pinpoint that.0922

Bilateral, literally meaning two sides.0925

Any animal that has a head and you can divide in half, and say there is the left and right side, like us.0930

Here is this person, if I divide this person in half.0942

If they are looking directly at us, this would be actually be the left and this would actually be the right, 0948

if that is the front of their body.0953

With bilateral symmetry, you get an interior end towards the head, you got a posterior end towards the bottom.0955

You will get a ventral side meaning that is towards the front door, dorsal side like dorsal fin.0962

All these terms come up with bilateral symmetry.0969

Even a simple worm is going to have bilateral symmetry because this one side that has the head with the mouth, there is one side that has the anus, with the eggs.0974

Depending on the worm, you will see how that some worms actually do not have two opening,0986

gut or digestive tract, but a lot of them do.0991

Asymmetry, there is really only one major phylum that typically has asymmetry, and it is the sponges.0993

In many ways, the sponges are barely animals.1001

Some things, they just do not have, in terms of those classic characteristics as animals.1005

In my opinion, sponges are kind of like glorified protists.1010

They have enough specialized tissues where they do belong in kingdom animalia.1014

Some sponges do have radial symmetry, but you will look down on sponges that kind of look like this.1018

Just these random shapes and you cannot divide it anyway, where you are like it is symmetrical.1025

No it is not, it has asymmetry, the lack of symmetry.1032

There are some exceptions, you can find sponges out there that do have radial symmetry.1036

Body cavities, a coelom is a fluid filled cushion between the gut and the outer body wall.1043

This is a good thing, the more advanced an animal, in terms of its body structure.1050

Especially, if you talk about animals that are solely on land, you are going to see a coelom.1056

That fluid filled cushioning that allows it to have protection for its inner parts and1063

not losing a lot of water or moisture, to the outer environment.1068

We have a coelum, thanks to that, we do not feel a lot of our interactivity on the surface of our skin.1073

If we had all the organs we have with no coelom, which would not be possible, but if we did,1081

you would feel every one of your little heartbeats ricocheting through your skin.1087

Every movement of your stomach would be like, you would feel on the outside of your body,1092

and it would be kind of disturbing.1098

But we do not have it, we have this fluid filled cushioning that arises from the mesoderm, 1100

that inner layer, the middle layer in that gastrula, from before.1105

Here the three main varieties, the reason why I just said two is acoelomates do not have the coelom.1110

With respect to this term, there are three varieties.1117

Acoelomates do not have this fluid filled cushioning.1119

I’m going to compare this to the three major phyla or groups of worms.1122

The flat worm, the flattest worm you can get like tapeworms, flukes, planarians,1127

you will hear more about them in animal lesson, part 2, these do not have a coelom.1135

When you talk about that inner gut area, it is adjacent to where their skin layer is,1143

that outer part of their body that arose from the ectoderm.1150

Pseudocoelomates is just this partial cushioning, it does not fully come from the mesoderm.1155

Sometimes, it is a derived from another one of those layers.1161

Roundworms, like the nematodes are pseudocoelomates.1165

Another example is rotifers, you will see a picture of rotifers, later on in the animal lessons.1171

That it is this partial cushioning not complete.1177

We are coelomates, we have a complete fluid filled cushioning arising from within the mesoderm.1180

An earthworm, one of the more advanced in terms of structure, types of worms, phylum annelid.1187

With the development of earthworm in its embryonic stage, if you do a cross section of it,1197

let us say here is the earthworm, and looked down it.1203

This is what you would see, the neural tube meaning what is eventually going to become their sensory chord,1207

which wills become the spinal cord, in us.1215

This neural tube which connects their nervous systems to body and all of this skin area, it comes from the ectoderm.1217

The gut in yellow, comes in the endoderm.1224

You could see that the mesoderm, this middle layer, kind of cushions and separates with fluid in the center,1227

the inner body cavity where the gut is and the outer area.1235

That is that whole coelom thing going on right there, there it is coelom.1240

For some major groups of animals.1249

The animal phyla, each one of these is a major phyla that you would see within kingdom animalia.1250

I do not have every single one of them but these are definitely the major ones.1256

At the end, I will actually tell you about one that is a little different and has one very unique kind of animal in it.1260

Because none of these other phyla really encapsulate, what is morphologically true and genetically true about this weird animal.1266

First one, phylum porifera, has a word pore in it, it is because those are the sponges.1274

With this particular sponge, it shows bilateral symmetry, if you look down these.1280

But in general, a lot of sponges are asymmetrical, like I mentioned earlier.1286

Phylum Cnidaria, that would be the sea jellies, sea anemones, the hydrazoens, and corals.1291

They definitely would be in coral reefs with a lot of these organisms.1300

Platyhelmininthes, nematodes, and annelids, these are the three major worm phyla.1305

Flatworms, unsegmented roundworms, and then annelids are segmented roundworms.1310

Here is the rotifers, these are really interesting,1316

typically microscopic aquatic animals that have cilia on their mouth, have the digestive tract.1320

Pretty interesting, for how small they are.1328

And then, phylum mollusca, a very extensive phylum, lots of different body plans.1331

They have three main things in common, all of them.1337

From clams, all the way up to an octopus, those are the mollusks.1341

The majority of them, in terms of the different varieties you would find in aquatic environments.1346

But a lot of them are adapted to life on land.1351

Phylum arthropoda, this would be your insects, your arachnids, a centipede, millipede, crustaceans.1354

This is the most abundant animal phylum on planet earth.1361

Impressive with how widespread they are.1365

Phylum echinodermata, the sea stars and sand dollars, and brittle stars and sea urchins,1367

we have all seen that shape in the water before or at least on a video.1376

Echinoderms means spiny skinned.1381

Actually, though they do not look a lot like us, in terms of their body plan, 1384

they have more in common with us, than you might think.1388

They are deuterostomes, like we are, rather than being protostomes like these others.1391

More about that term, later on.1396

Phylum chordate, that is our phylum.1398

Here is, he is a chordate, we are all chordates.1401

If you are wondering why are we chordates, what is the deal with that, why are we called vertebrates?1407

Underneath this phylum, you have subphylum vertebrata.1412

Because, some members of phylum chordata are not vertebrates, 1422

which means they would not be in our sub phylum within this phylum.1427

I will give you examples of those later on in the course.1431

Chordata is named after fact that we all have a notochord, which typically would become a spine,1435

if we are talking about vertebrates.1441

In some other organisms, it does not, it retain this flexible rod kind of structure, are getting hard and bony.1442

Another phylum that I do not have listed here, but I will give you an example is phylum tardigrada.1450

There is only one type of organism in this phylum, the amazing thing about that is phyla are really broad categories.1458

They are right under kingdoms, kingdom Animalia is all animals.1466

In this particular phylum are the tardigrades, also known as water bears or musk piglets.1471

They are using microscopic, some of them were like 1 or 2 millimeters long, they have 8 legs,1479

a hard outer coating, they are not quite arthropods and not quite worms.1485

They are not really directly related to any of these, but they are really strange animals.1490

They can actually completely dry up and go into a dormant state that can last for a decade or more without water.1496

And they can withstand huge amounts of radiation and heat, it is incredible what they can do.1504

Tardigrades, oftentimes are given their own phylum because they are so strange.1509

Let us talk about these individual phyla that I have listed before.1516

Phylum porifera, they have pores, they are also known as sponges.1520

They are exclusively in the oceans, lakes, etc.1524

They are known as protozoan, that is not eumetazoan.1528

Eumetazoans is a term for what we consider real animals.1533

Proto kind of meaning like early, the first, they resemble early animals,1539

in terms of their multicellularity being not as specialized, in terms of tissues like lot of other animals.1545

But they are in this kingdom, they do have enough characteristic in common with animals, 1551

so that they are not considered protists.1556

They are typically asymmetrical, there are some examples like this, where if you look down on them,1558

they have that radial symmetry.1562

But plenty of them have no symmetry at all, like I mentioned they are found in the ocean, some can be in freshwater.1564

They are filter feeders, they take in water into these pores and they expel it out of here, the waste water.1571

That is called an osculum, I will mention more about that in a second.1583

Adults are sessile meaning not motile.1586

Motile is a specific term in biology meaning, if you are mobile, if you can move as an animal, you are motile.1593

There you have motility as an adult, there is just anchored where they are at.1601

There is slight cellular movement inside of them, just like pump water in and circulate nutrients,1606

but they do not move as a whole.1611

However, their larvae are motile.1613

Once the sperm combines with egg and they released their larvae, little larvae swim around.1617

They will eventually settle somewhere, grow until their adult form, and be there the rest of their lives until they die or get eaten.1622

Structure, the osculum is that exit hole within a sponge.1629

They have these cells inside of them called archeocytes, sometimes called amoebocytes because they look like little amoebas.1633

Since they do not have real blood or circulation that you see in other animals, 1640

they have little cells that move around these archeocytes, and distribute nutrients and gases to the various tissues or cells.1646

It is definitely an adaptation that allows them to get by as a large multicellular being, compared to smaller protists.1656

Spicules, they do not have bones but they can have some rigidity, thanks to these.1665

They remind me of little jacks, if you have ever played jacks, it is that game where you throw the ball,1673

try to pick up the jacks and catch the ball before it bounces again.1684

I do not know if people play it anymore, but did little spicules, when they are taken out of a sponge,1686

they usually are white and hard, and they kind of can look like little jacks if you zoom in them up close.1690

It is the closest that sponges have to a skeleton, these spicules are usually made of silica,1696

calcium carbonate, help give them rigidity and some toughness structure.1702

And of course, they have pores, I already mentioned that.1707

Asexual or sexual reproduction, they have been known to regenerate, if they are cut apart.1711

They do release sperm that fertilize eggs, and other sponges.1717

They definitely can engage in sexual reproduction.1722

Here is another example of a sponge, very pretty one.1724

Phylum cnidaria, the cnidarians you do not typically pronounce the C.1730

It is the sea jellies, I know that you are probably used to hearing jellyfish.1737

I do not like saying that because they are not fish, they do not have eyes, they do not have scales,1743

they do not have spines, they do not have fins, they are not fish.1751

Let us call them sea jellies, that is a more proper term.1753

Sea anemones is another variety of cnidarian.1756

Hydrozoans, named after the mythical hydro, that dragon with lot of different heads, if you cut one off, it will regrow.1760

If you cut off one of these little tentacles, the hydrozoan can regrow it.1768

Zoan comes from the word zoo meaning animal.1772

It is an animal like a hydra.1777

Corals are kind of like apartment complexes for hundreds or thousands of cnidarians.1780

There are little chambers inside of the coral that have very tiny versions of being like this.1786

They just get nutrients out of the water and live there their entire existence.1794

They actually can build the coral from secretions that they make, that makes it that hard, rock like substance.1799

Scientists from hundreds of thousand of years ago had no idea that those are actually animals, 1807

those little animals living in there, because it is deceiving.1813

The corals are in the same phylum, as these other beings.1815

They have radial symmetry, whether you are looking at this one or looking at this one.1819

If you look down on it, you can cut it in half in number of ways.1823

The symmetry exists in sort of a round structure.1831

They do not have a true left and true right.1834

They have that circular kind of symmetry rather than bilateral.1837

They are mostly oceanic, you can occasionally find something in freshwater.1840

The vast majority of cnidarians are found in the oceans.1844

They have one gut opening also known as gastrovascular cavity.1847

They take nutrients in here, and they squirt it out, the waste through the same hole.1851

Same thing with the sea jelly, it will sting its prey with the tentacles more on that a bit, 1856

and then it brings it up into this area, digests it, and spits waste out through that same opening.1862

It actually is able to breathe through that same opening, by taking in oxygen and releasing CO₂.1868

That is why it is kind of 2 in 1, gastrovascular cavity helping get food in and circulate gases back in forth.1874

One gut opening, the same hole for food and waste, you could say their food taste like crap.1883

Terrible joke.1891

Body types, there are two main body types.1892

Here you are looking at a polyp and here you are looking at medusa.1895

The difference is like polyp is like this, medusa is like this.1912

With hydrozoans, usually this part of body is anchored somewhere or they can be floating around,1916

and they move their tentacles like this.1922

With the sea jelly, the tentacles are below and they move like this.1925

With some species, they are polyp their life or they are medusa of life.1931

With sea jellies, they start out as this colonial polyp form, that can be anchored in a coral reef.1935

It will do what is called budding, they will release little polyp babies into the ocean.1942

And then, as they mature their body inverts becomes the medusa.1947

And then, with sperm and egg they will make new polyps that get together and it starts all over again.1952

Sometimes, you do have the transition from polyp to medusa, others stay one of the other their whole life.1959

The way that I remember medusa is, I think about the mythological lady with the snake hair. 1964

I just think about like the snake hair going like this, with their whole live snakes, 1971

and try to turn people in this stone, when they look into her eyes.1976

You can see kind of like the way a sea jelly moves, it is similar to that, that is medusa.1981

Cnidocytes are stinging cells on their tentacles.1987

Within the cnidocytes, there is this structure called amedosis.1990

An nematocysts is what actually gets launched and does the stinging.1994

The trigger is that, when it gets touched, this little stinging barb that get shot out,2000

it happens in like hundreds of thousands of a second, it is crazy how fast it happens.2005

And it is great adaptation that allows members of this phylum to sting their prey, shock it, kill it, and take it in.2012

It is easier to find and eat food.2020

When you talk about anemones, they do the same thing.2023

An anemone, when it gets touched.2025

Sometimes, if an anemone is small enough, I have touched them, you do not get stung.2028

They are lots smaller, our skin prevents us from getting stung like a smaller fish or some other prey.2033

But when you touch it, they have an automatic reaction where they are trying to pull in food into their gut.2040

They are animals like the clown fish like what you see in Finding Nemo, the clown fish will not get stung by sea anemones,2047

it has this mutualism that it is adapted to living around that particular animal.2053

If you get stung by a sea jelly, do not have someone pee on it.2058

They have proven in the lab that urinating on a sea jelly sting does not actually help.2065

If someone insist that it deed, it is psychological.2070

They just heard that it helped.2073

In a lab, they showed that vinegar is actually what will kill nematocyst.2075

The pH, the acidic nature of vinegar, pouring in on the masses will stop them from their stinging,2084

and you will get some soothing relief, once you pour some vinegar on it.2089

They have a nerve net, when we talk about their nervous system.2094

It kind of just extends like a little net throughout their body.2097

They do not actually have a full on brain.2104

There is no concentrated central area where we can say that is a huge,2109

that is what we can call cephalization, which is common in another kinds of animals.2116

But they have this net like structure that allows their cells to communicate together as a whole.2121

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