How did life emerge on Earth? How have life and Earth co-evolved through geological time? Is life elsewhere in the universe? Take a look through the 4-billion-year history of life on Earth through the lens of the modern Tree of Life! This course will evaluate the entire history of life on Earth within the context of our cutting-edge understanding of the Tree of Life. This includes the pioneering work of Professor Carl Woese on the University of Illinois Urbana-Champaign campus which revolutionized our understanding with a new "Tree of Life." Other themes include: -Reconnaissance of ancient primordial life before the first cell evolved -The entire ~4-billion-year development of single- and multi-celled life through the lens of the Tree of Life -The influence of Earth system processes (meteor impacts, volcanoes, ice sheets) on shaping and structuring the Tree of Life This synthesis emphasizes the universality of the emergence of life as a prelude for the search for extraterrestrial life.
4.5. Invertebrates: Successes of Life Without a Backbone
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From the course by University of Illinois at Urbana-Champaign
Emergence of Life
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From the lesson
Week 4 - Paleozoic Life After the Advent of Skeletons
This week, you'll learn more about the Cambrian Explosion, which led to the development of external hard skeleton components at 542 million years before present. The initial successes of the invertebrates were shortly followed by the appearance of vertebrates with internal skeletons. Life then utilized these newfound evolutionary capabilities, beginning distinct cycles of radiation, diversification, and extinction, which define the three great Eukarya faunas of the Phanerozoic.
Meet the Instructors
Bruce W. Fouke, Ph.D.Director of the Roy J. Carver Biotechnology Center
Department of Geology, Department of Microbiology, and Institute for Genomic Biology
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I'm Carly Miller at the University of Illinois, and today we're discussing
invertebrate diversity or the different invertebrate phyla.
So remember, an invertebrate is an organism that is lacking a backbone.
And later, we will contrast that to
the sub phylum vertebrata which definitely has a backbone here.
So we're going to go through step by step the different phyla of invertebrates,
and what we want to identify is specific features that you can tie back
to a specific phylum.
And so we're going to go through symmetry, the modes of life,
the feeding modes, as well as any particularly special characteristics
that that particular phylum exhibits.
We're going to start with a very basic organism in the phylum porifera.
So, you may recognize porifera as sponges.
So sponges again, these are all going to be or
most of them will be marine organisms.
And then so we're going to start with sponges.
So again, these organisms are asymmetrical.
Some of them can be radial.
Their mode of life is that they're encrusters, meaning they grow on surfaces.
They grow on other organisms sometimes even.
They're epifaunal meaning they're on the sea floor, not within the sea floor.
And they're sessile.
So I don't know if you've ever seen a sponge move, [LAUGH] but I have not.
So that means that they're sessile.
Their feeding mode,
because they're sessile, they have to be filter feeders more or less.
So the phylum porifera, they are all filter feeders.
And there's one exception that is carnivorous.
The cellular structure of the phylum porifera
is that they don't really have any true tissues by definition.
So they are composed of cells but not a tissue,
which is a very specific organization of those cells.
Lastly, a piece of great information is that a group of sponges is called
a sleaze, [LAUGH] I've never heard that before, but [LAUGH] pretty interesting.
The next phylum we'd like to consider is the phylum cnidaria.
This is composed of corals, anenomes, and jellyfish.
So if you're thinking about a jellyfish that you may have seen or
a coral that you've snorkeled over,
what you might notice is that they are radially symmetrical.
The mode of life is epifaunal and sessile.
So again, corals are going to grow on the sea floor and
they're not going to move anywhere.
So, there are a few vagrant, or there are a few vagrant cnidarians,
but most of them are pelagic, and planktonic.
So remember that means they're kind of floating with the currents in the ocean.
So a jellyfish, it's radially symmetrical,
it's not going in a particular direction, but it does move.
So the phylum cnidaria, they are composed of carnivores so they are vagrant and
they actually are passive carnivores, meaning they can't hunt in a particular
direction or a particular food source, but they do eat live prey.
And how they do that is they use stinging cells called cnidoblasts, and those
are usually activated mechanically or by touch so that's why, other than preserving
corals, you're not supposed to touch them, is that they actually can sting you.
And I'm sure you've heard of jellyfish actually being quite dangerous or
deadly to humans because of these cnidoblast cells.
And so they're able to stun their prey and then ingest them.
Corals have stony skeletons and so they are well preserved in the fossil record.
They have a thin layer of soft parts, but
we have a great bulky skeleton that is then well preserved in the fossil record.
Additionally, organisms in the phylum cnidaria can be solitary, or
they can be colonial organisms.
So the functional unit of a colony is just one individual organism, but
each organism is then, either genetically identical or very similar to its neighbor.
And so those are put together in an assemblage called a colony.
Moving onto a much less dangerous phylum, this is the phylum bryozoa.
They're similar to a sponge maybe in structure, but
they're definitely within their own group and so these guys are mostly asymmetrical.
They're benthic, epifaunal, and sessile, so they're not going to be moving.
And we do have a couple of great fossils of different parts of the bryozoa,
not necessarily a full,
complete fossil of a bryozoan, because they're rather delicate, actually.
So here, you can see a stem, if you will, or
one of the more robust parts of a bryozoan organism.
Additionally, because we've mentioned that the bryozoans are epifaunal and
sessile, again meaning they're not going to move along that sea floor,
they are again going to be filter feeders.
The phylum bryozoa they have a specific feature called the lophophore and
they use this lophophore to filter feed, and
that's just a specific structure, that specifically the bryozoan use.
The next phylum we'd like to consider is brachiopoda.
Again, these are your brachiopods.
And they are widely distributed in the fossil record.
They're well preserved often.
And but there are several different shapes of brachiopods.
And I'll show you some examples that you can identify them.
A couple of the main features of this phylum is that their feeding mode is
that they're filter feeders.
Because again, we've identified that they're benthic, epifaunal, and
sessile, meaning they're not moving.
And these particular organisms are not colonial.
Brachiopods are similar to bryozoans in that they also use a lophophore.
So this particular structure is specific to the phylum brachiopoda and
the phylum bryozoa.
Brachiopods attached to the sea floor using a pedicle which is a fleshy
appendage which comes out the back of the shell and sticks to the sea floor and
they can use that pedicle for attachment.
Brachiopods also have a calcium carbonate exoskeleton.
So their shells are composed of calcium carbonate.
And what we want to note about the phylum brachiopoda is that they're one of
the most successful organisms in the Paleozoic era.
Lastly, we want to consider
the symmetry of brachiopods because it's specific to this phylum.
So the symmetry of these organisms is that it's bilateral symmetry but
it's perpendicular to the plane of commissure.
The plane of commissure is the surface or the plane where two shells come together.
For example, on this bivalve,
you can see that there's a top shell and there's a bottom shell.
And there's a plane that separates the two shells.
And that plane is called the plane of commissure.
So with brachiopod, they do have a top shell, and
a bottom shell, and a plane of commissure, but
their symmetry is such that it's not the same on the top and
the bottom but it's actually on the same from right to left.
We call that perpendicular to this plane.
So moving forward the next phylum we'd like to consider is phylum mollusca.
And so there's a diverse phyla of shelled organisms or formerly shelled organisms.
We've divided this phylum into many classes, but
we'd like to focus in on three particular classes.
The class bivalvia, the class gastropoda, and the class cephalopoda.
So the first class in phylum mollusca,
that we like to consider is the class bivalvia.
So these are clams, mussels, oysters, and scallops, for example.
Their symmetry is bilateral symmetry, but it's parallel to the plain of commissure.
This is again in contrast to the brachiopods,
which had symmetry perpendicular to that plane.
So, just to demonstrate that symmetry, we have a top shell and a bottom shell,
and we have our plane of commissure, which is that plane where those two shells meet.
And again, you can see here on this bivalve, that the top and
the bottom are mirror images of each other.
And so, the symmetry is along that plane and
that's parallel to the plane of commissure.
The mode of life of bivalves is epifaunal, but they can also be infaunal,
meaning they have the capability to bury themselves or survive on the sea floor.
The feeding mode of the class bivalvia is filter feeders and
they use a siphon to filter the sea water.
And it's similar to the structure of a lophophore, found in bryozoans and
brachiopods, but a little bit different, and is called a siphon, and
is specific to the class, bivalve, yeah.
And, just one note here, so
we talked about the symmetry being bilateral in general.
And parallel to the plane of commissure in this class, but oysters and scallops in
particular are generally asymmetrically actually so one will look out for that.
The second class that we'd like to consider in the phylum mollusca is
the class gastropoda or gastropods.
So these are snails, slugs, and
it can be very diverse as far as the level of species goes.
The symmetry of gastropods is that they're asymmetrical shells and
they have bilaterally symmetrical bodies actually.
The mode of life of the class gastropoda is that they're epifaunal, so
they live on the sea floor and they're vagrant, so they move.
So if you think of a snail or a slug, you know that those are moving around.
And you can think of a slug is an example of a bilaterally symmetrical body,
so that's a good picture that in your mind maybe what a slug looks like, splitting
it into right and left halves, and a snail is basically a slug with a shell, and so
you can picture how the shell is maybe asymmetrical.
But the organism that lives there, or the soft parts are bilaterally symmetrical.
And the feeding mode is interesting with the class gastropoda because
all feeding modes are represented even carnivores, so look out for those slugs.
The third class in the phylum mollusca is class cephalopoda or your cephalopods.
This includes squid, octopi, ammonoids, and
nautiloids, and many can be extremely large.
The symmetry of cephalopods is that they are bilaterally symmetrical,
with their bodies and their shells.
Their mode of life, if you can think of the squid, it's nektonic,
which meaning it's moving in a particular direction in the water column.
If you think of octopi, they are actually going to be benthic, but
obviously vagrant, they do move around.
And they are active predators so stay away.
Observe closely, but stay away.
And so if they're active predators,
then their feeding mode is that they are carnivorous.
Some cephalopods exhibit a single piece of a coiled shell.
[COUGH] So this is nautilus.
And they have a siphuncle in them, a siphuncle, which is a tube that brings in
water to the shell, and controls the buoyancy of it, in the water column.
Meaning it controls the position of the organism in the water column.
And an interesting note about cephalopods is that
they generally have above average intelligence.
So again, these are invertebrates, they're mollusks, and they are highly intelligent.
And this is correlated to actually very good eyesight.
And they're very fast movers, so I would beware of the class cephalopoda.
All right, moving to another phylum of invertebrates.
We want to consider arthropods, so the phylum arthropoda.
These are insects, trilobites which are extinct, crabs,
barnacles, spiders, scorpions, and lobsters.
Hm, add a little butter there, right?
Arthropods are the most successful and diverse, and
numerous organisms in one phylum.
So it's something to consider.
You want to note that.
This is a very diverse phylum.
Their symmetry is bilateral, though, so that's a specific symmetry.
So even though this phylum is very diverse, you have a lot of radiation
there, a high number of organisms included in this phylum,
they all are bilaterally symmetrical.
So we can gather some information from that symmetry again, but
the mode of life in the phylum arthopoda is, they can basically be anything.
And if you were paying attention to the list of examples, insects, trilobites,
crabs, lobsters, scorpion, you'll see that they're representing marine organisms,
freshwater organisms, and terrestrial organisms.
So a very diverse group here.
Their feeding mode, again across the board.
Something you want to consider, if you've identified an organism as an arthropod,
is that you need to pay very close attention to the shape, the structure,
the functional morphology of that organism so
that you can start to hypothesize what this organism ate and how it lived.
So one of the key characteristics of an arthropod is that it has a chitinous
exoskeleton, so an skeleton on the outside of the organism, and
is divided into segments which is usually where humans get a little weirded out.
So, here we have an example of an arthropod.
And this is a trilobite.
And again these are extinct.
But you can clearly see, it has segments where each of those body parts
are almost identical, if not identical to the one before it.
So it's a segmented organism.
And that's specific to arthropods, and again,
this trilobite fossil is actually a great one because it also
exhibits the bilateral symmetry that the phylum exhibits.
The last phylum we'd like to consider of invertebrates is called echinodermata.
So this is represented by sea stars, brittle stars, sea urchins,
sea cucumbers, sand dollars, echinoids and crinoids.
So their symmetry is pentamoral symmetry with some exceptions, and
they have a calcium carbonate endoskeleton, meaning inside their bodies.
So they're covered by a soft layer of tissue on the outside.
There's two classes we'd like to consider within the phylum echinodermata,
crinoidea, and echinoidea.
The first class is crinoidea, and
this is represented by sea lilies and crinoids, hence the name.
Living crinoids are generally unstocked, meaning they don't have the long stem,
a segmented stem, coming up to almost kind of a flowery shape,
I think these are sea lilies basically.
But so living crinoids are generally unstocked but
there have been reports in deep water that there are some stocked
crinoids still living today which is unusual.
Extinct crinoids were all almost by rule all stocked.
So if you had a chance to play in your playground as a child and
you had a gravel bottom to your playground.
You might have found something like this,
which looks like a segmented little peg if you will.
And I used to find these in my local playground and
I never knew what they were.
And here I am a geologist and I find out that these are crinoid stems actually.
And so they could several feet in length and
they actually they have easily observable segments.
And something you want to be aware of when you're considering a crinoid stock,
is that upon first glance they actually look radially symmetrical, right.
They're almost a perfect column or cylinder, but if you look closer,
you actually see that in the middle of a column there's a star,
or looks like a star.
If you were to count the points on the star, there's five, and so
that actually then knocks into the pentaradially symmetrical structure..
So crinoids are benthic, epifaunal organisms, and they're sessile.
So if you think about having a stalk.
That's not the same as a leg, right?
It's more like a stem.
And so that organism is going to be rooted to the sea floor.
So it's going to be benthic, and epifaunal, and sessile.
And because they're sessile, they're again going to be filter feeders.
The second class in echinodermata is echinoidea,
and there's regular echinoids and irregular echinoids.
Regular echinoids are sea urchins, and their epifaunal, their vagrant herbivores.
They scrape algae off the rocks with something called an Aristotle's lantern,
which we'll look at in closer detail.
Regular echinoids have long spines, actually, so
that's a key feature of those particular sea urchins.
An irregular echinoid is actually what you might call a sand dollar.
So if you think about a sand dollar, they're actually
rather flat, they're smooth, generally, in structure.
And they've actually been reduced to having
tiny spines as opposed to long spines with the regular echinoids.
So these irregular echinoids have greatly reduced spines.
They're still vagrant, but since they're smoother,
they can actually become infaunal and they can bury themselves in the ground.
So we have regular echinoids which are epifaunal and
we have irregular echinoids which are smoother and they're infaunal.
Additionally, irregular echinoids are detrital feeders meaning they
mix up the sediment and they actually eat the vitamins and
the nutrients that are buried within the sediment.
And the regular echinoids are herbivores.
So here we've considered a diverse group of invertebrates.
We've gotten very specific with the characteristics
that are exhibited within each phylum.
The important thing about what we've discussed is that you can deduce most of
that information from looking at a specimen that you find.
And so we can deduce a lot of information from the symmetry.
The shape of the organism, and those are very specific.
And so if you can identify those features, you can actually place this
organism taxonomically into a very particular phylum.
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