In this video, we're going to begin our introduction to archaea. And so the term archaea is actually a plural term, and the singular form is actually archaeon. And so these are referring to organisms in one of the three domains of life. And again, recall from our previous lesson videos that the three domains of life are bacteria, archaea, and eukarya. And so archaea is one of the major domains of life.
And so like bacteria, archaea also have a prokaryotic cell structure, which makes archaea prokaryotes along with bacteria. And for that reason, many students mistakenly believe that bacteria and archaea are identical because they're both prokaryotes, but that is not the case at all. It turns out that bacteria and archaea are as different from each other as they are from eukaryotes. And so there are still many differences between bacteria and archaea, although they are both categorized as prokaryotes. For example, archaea have unique ribosomal RNA or rRNA sequences that significantly differ from the ribosomal RNA sequences of bacteria and eukarya.
Also, archaea have cell walls that lack the molecule peptidoglycan, whereas recall from our previous lesson videos that bacteria have cell walls made of peptidoglycan. And peptidoglycan is really a molecule that is unique to bacteria, and archaea lack peptidoglycan. And so those are just some of the major differences between bacteria and archaea, but there are also other differences as well. Now archaea are well known for growing in extreme environments, and those that do are known as extremophiles because they can survive in extremely salty environments or extremely hot environments or environments that have extremely high pressures and things of that nature. However, although many archaea do grow in extreme environments and are extremophiles, there are some archaea that can grow in moderate environments as well.
And so they can be found in soils, and they can even be part of the human microbiota as well. And so if we take a look at our image down below, notice again on the left hand side, we're showing you a little snippet of our map of the lesson of the microbial world. And again, we're focusing in on the prokaryotes. We already talked about bacteria, and in this video, we're focusing on the archaea. And so you can once again see that both bacteria and archaea are classified as prokaryotes.
And again, although they're both classified as prokaryotes, meaning that they're going to be unicellular and that they're not going to have a nucleus, they have some similarities but they still have many differences. Bacteria and archaea are not identical. And so over here on the right hand side, we're showing you some examples of archaea. Some are going to be extremophiles in a way where they can grow in extremely salty environments, such as Haloquadratum walsbyi, and this is known as the salt square. And so you can see that it has this square-like arrangement, that it takes up.
And again, it is able to grow in extremely salty environments. Down below, we have some archaea that are capable of growing in extremely hot environments such as Pyrolobus fumarii, which is known as the fire lobe of the chimney. We also have Pyrococcus furiosus, which is known as the furious fireball, and then we have Thermococcus gammatolerans, which is known as the ball of fire. And so these are examples of archaea that can grow in extremely hot environments. And so, again, this here is just our brief introduction to archaea, and we'll be able to talk more about archaea as we move forward in our course.
But for now, this here concludes our introduction and we'll be able to get some practice applying these concepts as we move forward. So I'll see you all in our next video.