Cryptomonas borealis Skuja 1956

This is an organism I've wanted to illustrate for a while because it seemed interesting compared to other Cryptomonas species, with the "borealis" part and all that. I don't really have much energy to write this post, but I'll try anyway. Then, to feel less guilty, I'll see if I can get around to writing something for the final project. I should notify my supervisor for another mandatory review next week. What follows is a notice regarding the use of the images and taxonomic context, which is almost entirely copied and pasted from the other Cryptomonas guides, so don't expect much ingenuity there.

This species belongs to the family Cryptomonadaceae, order Cryptomonadales, class Cryptophyceae (commonly called "cryptomonad algae"). You know where this is going: cryptomonad algae are then included in the subphylum Rollomonadia, phylum Cryptista, subkingdom Hacrobia, kingdom Chromista. 

The kingdom Chromista is related to the clade Archaeplastida, which includes algae that are relatives and ancestors of plants. You might also encounter another classification, where the phylum Cryptista is included in the clade Pancryptista, which is related to Archaplastida, and both form the large CAM clade. But that's not really important; the point is that Cryptomonas borealis is another distant relative of plant ancestors.

bleeeeeh (˶˃ ᵕ ˂˶)

The following illustrations depict Cryptomonas borealis Skuja 1956, as the name is recorded on AlgaeBase. I have shown it in ventral view. The images are free to use and are also available on Wikimedia Commons. Of course, commercial use of these images is not permitted, nor is their use without proper attribution. "DOTkamina (2026)" is sufficient.

For the creation of these illustrations, as well as the text describing them, I have relied on and consulted the following works:

• "Chapter 18 - Cryptomonads". Brec L. Clay, 2015. Freshwater Algae of North America (Second Edition). Academic Press.
• "Cryptomonas borealis Skuja 1956". E.A. Molinari Novoa in Guiry, M.D. & Guiry, G.M. AlgaeBase. World-wide electronic publication, National University of Ireland, Galway. 2024.
• "Cryptomonas borealis Skuja, 1956". Martin Kreutz. Real Micro Life. 2021.
• "Light microscopical observations of the sigmoid species of the genus Cryptomonas Ehrenberg (Cryptophyceae) and their eventual pyrenoids". Pavel Javornický. Acta Musei Silesiae Scientiae Naturales. 63(1):1-24. DOI: 10.2478/cszma-2014-0001. 2014.
• "Revision of the Genus Cryptomonas (Cryptophyceae): a Combination of Molecular Phylogeny and Morphology Provides Insights into a Long-Hidden Dimorphism". Kerstin Hoef-Emden and Michael Melkonian. Protist: Volume 154, Issues 3-4, 371-409 pp. 2003.

Cryptomonas borealis is a rare species of Cryptomonas. 

Actually, it's not rare in any particular way; I just said that because the name sounded legendary. "B o r e a l i s"—few things surpass that in epicness. The C. borealis cell is oval with a wavy surface. In fact, I would describe it more accurately, in lateral view, as a kind of rectangular oval that has been bruised. It measures 20 to 50 µm in length.

The organism has two chloroplasts ranging in color from brownish to olive green. One would assume that both chloroplasts are the same color in each individual. In the ventral view, however, I have depicted each chloroplast as a different color: the "ventral" one more greenish and the "dorsal" one more brownish. But I'm sure that doesn't happen in real life. I made that decision to make it easier to distinguish both chloroplasts in the ventral view, but it doesn't mean they are bicolored in real life.

There are no pyrenoids; what exist are several hexagonal or oval starch granules. In the illustrations, I distinguish between "chloroplast 1 starch grains" and "chloroplast 2 starch grains," but this is purely for didactic purposes and to facilitate the separation of the two chloroplasts in the drawing. In reality, the starch granules of both chloroplasts should not differ in size, quantity, or color.

Furthermore, according to Clay (2015), I have represented two nucleomorphs as they are assumed to exist in Cryptomonas (one for each chloroplast, if there are two chloroplasts). Of course, their shape and location are almost speculative. Clay (2015) mentions that they are "between the pyrenoid and the nucleus," but I have represented them as being above the nucleus, since there are no pyrenoids in this species.

One notable feature of this species is the "gullet mouth," which is "widely open." This can be understood as the anterior part of the cell, where the vestibulum and gullet are located, being especially wide. It doesn't end in a "point" or a "curve" as occurs in other Cryptomonas species. In fact, from a lateral view, it literally resembles two jaws or "protrusions" surrounding the entrance (vestibulum), like "a fish with its mouth open," according to Kreutz (2021). I believe I've managed to represent this in my illustration, but you can check Kreutz (2021), Figure 1b, to get a better visualization. Furthermore, this arrangement results in one side of the cell around the vestibulum appearing more "prominent" than the other. In this case, the more prominent side is the dorsal side; you'll see that it's higher on that side than on the ventral side. This prominent area is known as the "apical rostrum."

The gullet, btw, reaches up to half the length of the cell and is covered with ejectisomes, as is common in other Cryptomonas species. In the illustrations of the organism in Kreutz (2021) and Javornický (2014), it appears that the ejectisomes do not completely cover the gullet; rather, there is a portion closer to the exterior ("the vestibulum") that is not covered by them. And that is how I have represented it.

The vestibulum has a "vestibular ligule," a characteristic of campylomorphic Cryptomonas species, such as C. borealis. However, this structure is almost speculative because it has not been reported for this specific species; rather, it is a characteristic that is "assumed" for campylomorphic Cryptomonas. You can learn more about this morphology in the entry on Cryptomonas obovata.

According to Hoef-Emden and Melkonian (2003), the furrow is curved, and I would venture to say that it extends to just under half the length of the cell, based on what I can observe in Hoef-Emden and Melkonian (2003): Figures 2 and 10. That is my main excuse for having depicted the large furrow.

Two Maupas bodies are represented, although the species can have as few as one, or even as many as three. The contractile vacuole is located anteriorly, beneath the apical rostrum. There is also a nucleus with a nucleolus located posteriorly, "in posterior third" (Kreutz 2021). I assume the nucleolus exists because, according to Clay (2015), in cryptomonads during interphase (the "normal" phase of cell life where it is not dividing, but simply existing), the nucleolus is "prominent and persistent."

I have drawn the endoplasmic reticulum, Golgi apparatus, and the single reticulated mitochondrion. The shapes of these structures are speculative. In the case of the mitochondrion, it's a predicted reticulated shape based on what Santore and Greenwood (1977) explains, where it's mentioned that Cryptomonas has a single mitochondrion with numerous branches distributed throughout the cell, concentrated in areas like the gullet. It's assumed that these mitochondrial branches should have different thicknesses in various sections, but in my drawing, the width of these branches is almost uniform.

I assume that the flagellar arrangement in C. borealis is type 4, as described in Kugrens et al. (1987): this means: the flagella do not follow the basic type 1 flagellar arrangement (long dorsal flagellum with two rows of mastigonemes, each with a terminal filament; short ventral flagellum with one row of mastigonemes, each with two unequal terminal filaments). Instead, there is a type 4 flagellar arrangement. In this arrangement, there is only one row of mastigonemes for both flagella. The nature of the terminal filaments is the same as in type 1 flagella. Therefore: long (dorsal) flagellum with one row of mastigonemes, each with a terminal filament; short (ventral) flagellum with one row of mastigonemes, each with two unequal terminal filaments. Additionally, at the terminal tip of the long flagellum, there are four "terminal hairs".

Kugrens et al. (1987)'s work does not mention that C. borealis has type 4 flagella. I infer this because its morphological relationship with C. curvata and C. platyuris, among other species, has been discussed (Javornický 2014 and Hoef-Emden and Melkonian 2003). And C. curvata and C. platyuris have type-4 flagella. Furthermore, flagellar type 4 in Kugrens et al. (1987) is associated with species described as campylomorphic by Clay (2015)... and C. borealis is campylomorphic and only has this morph according to Hoef-Emden and Melkonian (2003). All of this leads me to believe that C. borealis has this flagellar arrangement. But of course, this is speculative, and electron microscopy studies would be necessary to confirm it.

Both the mastigonemes and the additional filaments and hairs can only be seen with an electron microscope. Don't expect to see them with a light microscope. Even the flagella are sometimes difficult to see with a light microscope. I almost forgot: both flagella are located on the right side of the vestibule. That's from a dorsal view. In a ventral view, they appear to be on the left, but that's just an illusion!

I really think that was all I had to say about this species. I've had it ready for a long time—I mean, the illustrations—but I was too lazy to write it. Thankfully, I'm finally out of writer's block.