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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.

Alveolates

Taxonomy is tricky. Trying to figure out what’s related to what, how certain features and traits are derived; it’s hard work.

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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.

Ciliates

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.

Apicomplexans

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.

Dinoflagellates

Now, when we’re talking about the diversity of living things, we really can’t skip over this last major group of alveolates, the dinoflagellates.

Dinoflagellates are defined by two main characteristics. For one, most of them have an armor-like plating over the cell membrane. The other defining trait is the presence of perpendicular flagella, or long thin tails used for swimming, that give the cell a spiraling, spinning motion.With over 2,000 known species, the dinoflagellates are incredibly diverse. Some are predators, others rely on photosynthesis to make food, and some are parasites. Some are bioluminescent, meaning they glow like fireflies, and some can even change the color of water.

This is called a bloom, and it happens when dinoflagellates reproduce so quickly that there are enough of them to create a visible ribbon of color. It sounds cool, but it can actually be dangerous. When certain marine species do this it creates a red tide, a bloom of dinoflagellates that produce a neurotoxin that can kill fish and be harmful to humans as well. It’s amazing how something so little can cause such a big problem.

Lesson Summary

A living thing that has cells with membrane-bound organelles but is not an animal, plant, or fungi is called a protist. This is a diverse group of creatures, and within it are several smaller groups, which are also pretty diverse.

The alveolates, protists characterized by the presence of sacs of fluid under the cell membrane called alveoli, are one such group. Alveolates themselves are pretty diverse, with three major groups.First are the ciliates, characterized by short, hair-like structures called cilia that cover the cell. Cilia are used to help the cell get around, as well as for catching prey.

The next group of alveolates is the apicomplexans, so called because of an asymmetrical collection of alveoli at one end of the cell known as the apical complex. Apicomplexans are parasitic and include the parasites that are responsible for malaria. Finally, we’ve got the dinoflagellates.

Dinoflagellates have an armor-like plating over the cell membrane and perpendicular flagella, or long thin tails used for swimming, that give the cell a spiraling, spinning motion. When they reproduce quickly they can create blooms, which can become harmful. So, there you go. Just another brief glimpse into some of the incredible diversity of life on this big, strange planet of ours.

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