[MUSIC] You have heard about one of the six eukaryotic super kingdoms now, the Archaeplastida, that includes the red and the green algae and plants which were organisms that most of you are familiar with. The next two super kingdoms I'm going to talk about are called the Excavata and the Rhizaria, and they accommodate only single-celled organisms, and many of them are probably organisms that you have never heard about before. This doesn't mean that they are rare, or they are difficult to find though. In fact, I guess that I've just caught some of them with a plankton net in the pond here and have them in this bucket now. So let's try to take a look at the plankton we just got. While we have someone looking into our samples, we can take a look at some of the excavates and see what kind of organisms we are dealing with. As you can see here in the photo, they are all tiny, microscopical organisms, and it's really hard to say what they have in common besides being small. The reason why we still think that they are related to each other though is because of comparisons of the DNA, and it suggests a close relationship. In other words, the group Excavata is supported by molecular data only and not by their morphology. The only morphological character that eventually could apply is the presence of a so-called food groove, which is the longitudinal furrow that you find in many excavates. However, since we also have many excavates without this food groove, we don't really know whether it was an original character for the whole group, or whether it developed inside the group. But let's take a look at our sample now, and see what we found. What we have here is a quite common excavate organism. It's called Euglena, and you can see that it has this distinct red eye spot and lots of chloroplasts that gives it the beautiful, green color. It also has this food groove that I mentioned, but it's difficult to see in the photo. This organism is very common in fresh water, and if you have worked with aquatic plankton samples, you might very well have seen it before. Another less pleasant member of the Excavata that you might have heard about before is Trypanosoma. Perhaps you haven't heard the name Trypanosoma before. But if I say sleeping sickness, I guess most of you know what I'm talking about. Sleeping sickness is a quite unpleasant tropical disease, and many people associate it with insects, the tsetse fly. However, the tsetse fly is only the vector that carries the disease. The real bad guy in this context is Trypanosoma that gets transferred from the fly to the human lymphatic system, and later on, attack other organs, including the nervous system. Hence, even though they are small, the excavates still represent organisms with a great impact on humans and nature. But now, let's move on the next super kingdom. The Rhizaria has several things in common with the excavates. We're dealing with a group with single-celled organisms again. And we're dealing with a group that is supported by molecular sequence data only. It's a group where most people might not be very familiar with the organisms in it. But again, we would actually be able to collect some of the group's members right here in this pond. Here you see some examples of different rhizarians. And I guess you would agree with me that many of them look strange. Some of them are amoebae-like. But they should not be confused with the true amoebae that have their own superphylum. But it's not all of them that are soft and blobby, many rhizarians come with hard parts, either as an external shell or as an internal, mineral skeleton. Again, we might not feel very familiar with these organisms. But I've tried to come up with a couple of examples of the rhizarian groups that you might have heard about before. Look at this photo, for instance, this is a radiolarian. You might have heard the name before. They are planktonic organisms that float around in the water. Most of them are marine, but they might also be found in fresh water as well. If you look at the photo, you can see that it has some external, soft parts, but internally, they have a mineral skeleton. This skeleton helps to support the amoeboid soft parts, but it's also a great help for paleontologists because it fossilizes very well. In fact, we have radiolarian fossils going all the way back to the early Cambrian, which means that radiolarians are actually just as old as the animal kingdom. One of the most well-known Rhizarian groups is probably the Foraminiferans or simply, the Forams. They are shelled amoebae-like organisms and as you can see, they might come in many different kinds of shapes. Some of them look like stars or even little Christmas trees. And other even resemble little snails so much that they actually, back in time, were grouped together with the snails and the mollusks. The known species are almost exclusively marine and almost exclusively benthic, which means that they are found in the seafloor sediment. In certain cases, they may be so numerous that it's actually dead forams that make up the sediment. Because they have this hard shell, they are easily fossilized also. And just as it was the case with the radiolarians, we have fossils that trace forams all the way back to the early Cambrian. Now I just said before that all Rhizarians are single celled. This is correct, of course, but being single celled doesn't necessarily mean that you have to be small. Now, check out this giant foram here. It's single celled, but actually, it's so large that you can see it with your own eyes. This specimen is at least 15 centimeters in width. The single cell inside it is, of course, cell microscopic. But this deep-sea foram called Stannophyllum keeps adding shells outside on its cell, so that it may grow to sizes even larger than 25 centimeters, almost 10 inches. So you see, single cells doesn't necessarily mean small. [SOUND]
