Alveolates: Dinoflagellates, Apicomplexans & Ciliates

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  • 0:00 Alveolates
  • 1:19 Ciliates
  • 2:19 Apicomplexans
  • 3:20 Dinoflagellates
  • 4:41 Lesson Summary
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Lesson Transcript
Instructor: Christopher Muscato

Chris has a master's degree in history and teaches at the University of Northern Colorado.

As one of the most diverse taxonomic groups, the protists encompass a wide range of species. In this lesson, we'll check out the group called the alveolates and explore what makes each of the three types unique.


Taxonomy is tricky. Trying to figure out what's related to what, how certain features and traits are derived; it's hard work. A lot of the living things on this planet are similar enough to be categorized as animals, plants, or fungi. But, there are also many species that aren't quite any of these. A living thing that has cells with membrane-bound organelles but is not an animal, plant, or fungi is called a protist. With such a loose definition, it's really no surprise that this group is incredibly diverse.

Within the protists is one group where this diversity really gets to shine. The alveolates are protists characterized by the presence of sacs of fluid under the cell membrane. These sacs, which are fluids enclosed by lipid fat or wax, are called alveoli, hence the name alveolates. The exact function of the alveoli is unknown, but it could be for strength or temperature regulation. So, the presence of alveoli defines the alveolates, but like I said, this is quite the diverse group. So to understand what they look like, we're going to have to look a little bit closer.


Alright, first up on our tour of the alveolates is the group called the ciliates. This single-celled creature is a ciliate. See those short, dense, hair-like structures covering the outside of the cell? Those are called cilia. Cilia are used to help the cell swim around, as well as to catch passing prey. Yes, prey. Ciliates are predators; they eat other microorganisms. Those cilia are very important to the cell, and in fact, the presence of cilia is the defining characteristic of the ciliates. Beyond that, however, this is a very diverse group of creatures. There are over 7,000 known species of ciliates, and some of them can get pretty large, at least by protist standards. The largest ciliates are about 2mm long! That may not sound like much to us, but for a microorganism, that's pretty huge.


Ciliates are pretty cool, but they're not the only group of alveolates out there. Next we've got the apicomplexans. This group is characterized by an asymmetrical collection of alveoli at one end of the cell, which is called the apical complex. Apical complex, apicomplexans, biologists are really creative, aren't they? Anyway, the apical complex is shaped the way it is because it helps the cell latch onto and infect other cells. That's right, apicomplexans are parasitic. There are 4,000 known species of apicomplexans, all of them parasitic, and some of them pretty nasty. Ever heard of the disease malaria? Humans get malaria when they are infected with apicomplexans within the genus plasmodium, just one of several groups of apicomplexans. So, they may be tiny, but they're definitely not something to be taken lightly.

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