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We start the unit about invertebrates, that is, the animals that lack, that do not have a vertebral column.

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The first group of invertebrates we are going to study are sponges.

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Sponges are called by scientists phylum porifera, but for me it is enough that you remember sponges,

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which, as you know, are aquatic animals.

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Aquatic animals that cannot move from place to place. They live in one place and that is where

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they spend the rest of their life. Although, as we will study later, that is what happens when they

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are adults. When sponges start their life as larvae then they are able to move as we will see later.

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We have the idea that sponges are squishy and soft but actually most of them are not squishy

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and soft most of them are hard okay and that is because they have a skeleton composed of

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microscopic needles those microscopic needles are called spikeles okay so they are not squishy

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they are hard and their shape is cylindrical so scientists say they have radial symmetry

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radial symmetry means they do not have a right and left side but instead they are approximately

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cylindrical okay so they do not have a right and left side but they are the

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same all around in their shape. The way sponges get food is by filtering water

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so they cause water to move through them to get food particles from the water so

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here you have a drawing of a sponge and as you can see with the arrows what is

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going to happen is that water enters through the sides okay sponges are full

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of little holes on the sides here you can see the name of those holes so water enters the sponge

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then the sponge gets the food particles from the water and expels the water through the top

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opening which is called the osculum how do sponges move the water inside the sponges you can see

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there are special cells and these cells have like one tail each cell okay then those tails are

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continuously rotating and by rotating they cause the water to move and the water moves in the

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direction i told you those cells that move water are called coanocytes each coanocyte has a tail

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that is called a flagellum similar to the tail of sperm cells in humans so it is the movement of

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that flagellum that moves the water to create water currents. This can be seen

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in a video that I have in my website, although now we are going to watch it in

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a short way. In this video you can see a sponge and then a diver is going to

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release some water with color besides the sponge. So the water is on the side of

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the sponge, we can see it because of the yellow staining, and now the stained

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water is inside the sponge, it has entered through the side and it exits

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through the top opening, the osculum. Then here again we have two sponges, again the

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diver is going to release stained water besides, okay so on the outside we have

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that stained water but then the water is going to come inside the sponge and then

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it is going to be released through the osculum which is the top opening.