Word of the day: protoctist

Today’s word is fairly hardcore. A couple of months ago, I talked about the different ways scientists (biologists, taxonomists, zoologists, botanists, etc.) categorize life on Earth into five kingdoms (the Prokaryote superkingdom consisting solely of Bacteria, and the Eukaryote superkingdom, which contains the remaining 4 kingdoms: Protoctista, Animalia, Fungi, and Plantae).

Since then, I’ve been reading a lot of fun stuff (Tolkien, Herbert, comic books, Elmo board books, find the truck/train/car/plane/boat books), and hadn’t gotten back to my Margulis and Chapman until today. After all, it has a Lot of Hard Words In It.

But I knew I had to come back to it at some point, because I was curious about that first eukaryote kingdom, Protoctista. I mean, what the heck is that, anyway? Well, according to M & C,

Kingdom Protoctista comprises the eukaryotic microorganisms and their immediate descendants: all algae, including the seaweeds; undulipodiated mastigote molds, water molds, the slime molds and slime nets; the traditional protozoa; and other even more obscure aquatic organisms. Its members are not animals (which develop from a blastula), plants (which develop from maternally retained plant embryos), or fungi (which lack unulipodia and develop from fungal spores). Nor are protoctists prokaryotes. Protoctist cells contain microtubules, nuclei, and other characteristic eukaryotic features…. Many photosynthesize (have plastids), and most are aerobes (have mitochondria)…. (120)

I warned you that there were A Lot of Hard Words. This is just part of the first paragraph of the introduction to this kingdom. Keep plugging away. The real juicy bit is right ahead:

All protoctists evolved from symbioses between at least two different kinds of bacteria—often many more than two.

Cool, huh? Just like us, these leetle teensy-tinsy organisms (well, seaweeds can get pretty big… oops! don’t want to give away the point of this post!) evolved from bacteria.

But why do we have to call them protoctists? What’s wrong with the good old shorter word protists? I’m glad you asked. I’m even gladder that M&C have the answer, so I don’t have to do too much more research:

Why “protoctist” rather than “protist”? Since the nineteenth century, the word protists, whether used informally or formally, has come to connote a single-celled or few-celled tiny organism. In the past three decades, however, the basis for classifying single-celled organisms separately from their multicellular descendants has weakened. Multicellularity evolved many times in unicellular organisms. Many multicellular beings are far more closely related to certain unicells than they are to other multicellular organisms….

We adopt the concept of protoctist propounded in modern times by Californian botanist Herbert F. Copeland in 1956. The word was introduced by English naturalist John Hogg in 1860 to designate “all the lower creatures, or the primary organic beings;—both Protophyta, … having more the nature of plants; and Protozoa … having rather the nature of animals. Copeland recognized, as had several scholars in the nineteenth century, the absurdity of referring to a giant kelp by the word “protist,” a term that had come to imply unicellularity and, thus, smallness. (122)

In other words, calling this kingdom Protoctista allows us to avoid lumping most of these organisms in with the other three eukaryote kingdoms,* all of which are inherently multicellular, but still allows us to include large multicellular organisms in as needed (like those giant seaweeds I was talking about earlier).

All protoctists are aquatic: marine, freshwater, terrestrial but needing moist soil, parasitic in moist tissues of other organisms. In fact, according to M&C, “nearly all animals, fungi, and plants—perhaps all—have protoctist associates” (123).

The best part about protoctists, though, as with almost all the organisms in M&C, is the pictures. These things have some amazing body plans. Too bad you have to shell out the money for the book to get a really good feel for what I’m talking about.

Maybe at some point I’ll be able to put this book down and move on into the other kingdoms, but for now, Rhizopoda, Granuloreticulosa, and 34 other phyla of protoctists have my attention. They don’t have much of a plot, though…

* Bonus points to those of you who can name those other three kingdoms without Googling! (All you have to do is read this page again; this is not a hard quiz, even if it does have Hard Words.)