Hello marine biology students.
This week we're going to be talking about
invertebrates in the ocean.
These are animals without a skull and a backbone,
and the first that we'll be talking about
is the simplest, the sponges.
[Intro Music]
So we'll be discussing many invertebrate phyla
this week in lecture.
So what is an invertebrate?
Well, animals without a backbone are known
as invertebrates, whereas if an animal does
have a skull and a backbone, then it is a
vertebrate.
Turns out about 97% of all identified animal
species fall into this category of invertebrates.
They're by far the most abundant and diverse
categories of animals.
All major animal groups or phyla have marine
representatives, meaning individuals who live
in the marine environment.
There are no phyla which are exclusively terrestrial.
However, there are several phyla that are
exclusively marine, meaning they only live
in the oceans.
So let's look at what it takes for something
to be considered an animal, and then we'll
talk about the different groups of animals.
For something to be an animal, it needs to
be eukaryotic, multicellular, and often with
tissue-level organization.
Although as we'll see with one animal group,
they lack that tissue-level organization.
Animals are heterotrophs, meaning they aren't
photosynthetic.
They have to feed on other organisms, they
cannot feed themselves with sunlight.
Animals require oxygen for aerobic respiration.
Because they are multicellular, they often
have high energy demands.
They need to have oxygen present for the breakdown
of food for energy.
And lastly, most are mobile.
At least during some portion of their life,
meaning they can move, although, in certain
organisms, in their adult stage they will
be sessile or non moving.
So when we talk about animals, we need to
discuss how their body is organized, and it
turns out there's a few different symmetry
plans when it comes to basic body characteristics.
One is radial symmetry.
With radial symmetry, there's clearly a top
and a bottom of the organism, but there isn't
clearly a right or a left side.
You could almost imagine a terracotta flowerpot,
which is open on one end and closed on the
other and you can rotate it 360 degrees and
you aren't going to clearly see that one side
is different from the other side.
That is radial symmetry.
Conversely, bilateral symmetry, bilateral
symmetry is when we have clear top and bottom
and it can be split down the middle and right
half and left half will be symmetrical to
each other, but they will be distinct.
They will be mirror images of each other.
And then lastly, organisms that lack tissue
organization often lack body plan design or
symmetry and so we call these asymmetrical.
So asymmetrical animals, they don't have a
defined distinct body plan and those will
be the ones we're looking at in this first
group, the sponges.
So here we can see examples of radial symmetry
and bilateral symmetry.
With radial symmetry, again we can see that
it doesn't matter which point you divided
from that center point, the two halves are
going to look the same, whereas with bilateral
symmetry, there's a clear front and back,
top and bottom, left and right and it's symmetrical
along one plane of similarity.
So, looking at our major invertebrate phyla,
we have the Poriferans which are the sponges,
which we'll be talking about in this video.
The Cnidarians and the Ctenophores, which
we'll talk about in our next video.
Those are going to be things like jellyfish
and coral and comb jellies.
Then we have some bilaterally symmetrical
worms, and we'll talk about those in one group,
but they are phylum Platyhelminthes, which
are flat worms, then Nemerteans, which are
ribbon worms.
Nematodes, in phylum Nematoda.
Arrow worms in phylum Chaetognatha, and then
also our segmented worms in phylum Annelida.
The next group that we're going to look at
are the molluscs in phylum Mollusca, arthropods
in phylum Arthropoda, and then a group of
organisms that have a similar feeding structure
called a lophophore.
These are the lophophorates, the Bryozoans,
the Phoronids and the brachiopods.
And then, we'll finish things off with our
discussion of the echinoderms and then the
hemichordates and the chordates.
So quite a list of invertebrate phyla, although
believe it or not, this is probably only about
half of the phyla in the animal kingdom.
So sponges, phylum Porifera.
The basic characteristics of the sponges is
that they are sessile as adults, so they're
attached.
They don't move as adults.
There are numerous tiny pores on the outside
of the body known as ostia, which allow water
to flow in through them and that's really
how the sponge is going to be getting its
nutrients, by filter feeding water as it comes
into its body.
The water flow will also carry waste and gametes
away.
Sponges are primarily found in the marine
environment.
As I had mentioned, they have an asymmetrical
body plan, meaning that there's no defined
symmetry to their body shape.
When we look at the types of cells that make
up sponges, there are a few different types,
although they are not organized into tissues.
So, the first cell type we'll talk about are
the collar cells, also called choanocytes.
These choanocytes, they have flagella and
a collar of cilia on one end of the cell.
These choanocytes line the interior canals
of the sponge.
And the flagella they have create water currents
that causes the circulation of water through
the sponge.
This circulation of water brings food in from
outside, also again carries wastes and gametes
out.
So, it's the collar on the choanocytes that
end up capturing the food particles that are
brought in by the water current.
Now, another type of cell that are in the
sponges are going to be the pinacocytes and
these are flattened cells that cover the exterior
of the body, almost like a layer of skin or
a layer of protection.
Another type of cell in the sponges are the
porocytes.
And these porocytes can regulate the amount
of water entering the sponge at different
areas.
When we look at this diagram of sponges, we
can see the general vase-like structure with
ostia leading in and then the oscullum being
the major out current of the water.
And then, as we zoom in and look at the side,
we can see the pinacocytes making up the boundary,
the porocytes controlling the pores, and the
choanocytes that are in the interior chamber.
Now, another type of cell we haven't quite
talked about yet are the amebocyte cells and
they can wander around the inside of the sponge.
They have a variety of purposes, but some
of the important ones include generating spicules
and also Spongin.
When we look at the structural support of
a sponge cell, it's full of this elastic protein
fiber known as Spongin 
and that's where some of its structural integrity
comes from.
Some sponges will also have spicules, and
these spicules can either be made out of silica
or a calcium carbonate.
Spicules come in a variety of shapes, from
simple rods to star shapes.
In fact, there are some that look exactly
like the star of the Mercedes Benz symbol.
Now, both of these structures, the Spongin
and the spicules, are secreted by internal
wandering cells called amebocytes, and these
amebocytes can actually also become the other
type of sponge cells as well.
When it comes to reproduction, sponges are
able to reproduce both asexually and sexually.
Asexual budding 
is one form of reproduction in which a larger
adult starts just forming smaller individuals
that separate and are able to live on their
own.
They break off and they grow into a new sponge.
Experiments were done to separate the cells
of a sponge by pushing that sponge through
a sieve or through some screen mesh, and in
that way, the sponge cells were separated
from each other.
But in a petri dish, those sponge cells would
end up finding neighboring cells and they
would end up forming structures together,
forming new individuals.
Now, a surprising thing was that if multiple
sponges of different species had their cells
separated in this way and were set to grow
in a petri dish, the cells of the different
species would actually separate and segregate
from each other.
So you would end up with small little clusters
of sponge cells of different types.
So there's some form of recognition between
the cells as to what species they belong to.
So, experiments with artificial reproduction
by fragmentation showed, again, that when
those sponges were pushed through sieves,
they will reform into smaller individuals
and that different species of sponges seem
to recognize their own cells.
Sponges also reproduce sexually.
The sexual reproduction of sponges involves
sperm cells of the sponges being brought in
by the water currents and finding an egg that
is found within the interior of that sponge.
Fertilization takes place developing into
an embryo and then a larva.
That larva is then released from the excurrent
siphon and it can travel a certain distance
from the parent and then settle into its own
adult sponge.
So while adult sponges are not motile, the
larvae can travel a certain distance before
forming a new sponge.
Most sponges are hermaphrodites, meaning they
can produce both male and female gametes.
So that finishes our introduction to the sponges.
Now, before our next video I would like you
to think about what it would be like not to
have a right side and a left side.
We'll talk about that in the next video.
