Wow, I'm finding it hard to write this. I've gotten so sleepy, you know, the kind where you dream you're dreaming. I think I'll leave the writing for tomorrow. But I'll be back, I swear.
(๏ᆺ๏υ)
Well, here I am, two days later. Or is it three? I don't know. It's just a quick announcement that I've at least managed to finish the text for the final project. I hope to talk about it in another post. This post is dedicated to something that motivates me more: a new illustration of a protist.
Friendly screamer!: The illustrations are free to use under CC BY-SA 4.0, non-commercial, attribution required (DOTkamina 2026). I cannot continue without first thanking Drahomíra Faktorová, PhD, who provided me with the complete paper "Diplonemids - A Review on 'New' Flagellates on the Oceanic Block" (2022). It's a text I really needed to check out regarding peripheral lacunae, which I discuss later. Thank you very much!
This time, I was feeling pretty discouraged, so I chose the first one that came up randomly. It turned out to be Hemistasia phaeocysticola. This is an organism from the family Hemistasiidae, order Diplosonematales, class Diplosonematophyceae, superclass Diplonemia. According to Wikipedia, the order Diplonemida, in the class Diplonemea, also appear to be synonymous.
In any case, these organisms, including Hemistasia phaeocysticola, are referred to as "diplonemids." They are generally heterotrophic, biflagellate protists that prey on other protists. They primarily inhabit marine waters, but are also found in freshwater. The genus Hemistasia is, in fact, a predator: diatoms, dinoflagellates, haptophytes, and even copepods (which are no longer protists, but rather entire microscopic animals). Diplonemids appear to be very abundant in the oceans and play an important predatory role, especially Hemistasia.
The information in the previous paragraph came from "Diplonemids" by Julius Lukeš, Olga Flegontova, and Aleš Horák (2015). They also explain a fundamental difference between diplonemids and kinetoplastids at the level of mitochondrial DNA and its transcripts. I'm not a big fan of genetics, so I'll leave the paper there for you to read yourself.
Diplonemids are the sister clade to the kinetoplastids (class Kinetoplastea), a group that includes free-living organisms (for example, eubodonids such as Bodo saltans, neobodonids such as Klosteria bodomorphis, which I have illustrated previously); as well as parasites, such as the mythical trypanosomatids (Trypanosoma, Leishmania, Phytomonas, etc.).
Diplonemea, along with Kinetoplastea, make up the subphylum Glycomonada, which is included in the phylum Euglenophyta (therefore, euglenas are distant relatives), infrakingdom Discicristata (where the sister clade to euglenophytes are the percolozoan amoebas such as the brain-eating amoeba Naegleria fowleri), clade Discoba (where discicristata are a sister group to jakobids and Tsukubamonads), domain Eukaryota. I think that's a good overview of the relational biodiversity with H. phaeocysticola.
In short, the illustrations presented here, as well as the information to describe my drawings, I have taken from the work: "Hemistasia phaeocysticola (Scherffel) comb. nov., Redescription of a Free-living, Marine, Phagotrophic Kinetoplastid Flagellate" (1996), by Malte Elbrächter, Eberhard Schnepf and Ivonne Balzer.
Well, the rostrum is simply the term for the extension of the anterior part of a cell, like a beak or snout, which in H. phaeocysticola has a more or less triangular shape. The rostrum is densely covered with hair-like structures (rostral hairs), 0.2 µm long. The rostrum also houses a "mouth" (the cytostome). The cytostome is described as a furrow located between the curvature of the rostrum above it (known as the "preoral crest") and a small cytoplasmic extension subapically adjacent to the cytostome (the "cytostome lip"). The cytostome connects to a cytopharynx, which is located ventrally.
Near the rostrum is the flagellar pocket, a deep invagination similar to the gullet of cryptophyte algae (some of which I have illustrated previously—explore the blog! But be discreet). From the bottom of the flagellar pocket emerge two unequal flagella, often twisted around the cell. These flagella are, in fact, axonemes (with a typical 9+2 configuration: nine microtubular doublets surrounding two central microtubular singlets) covered by a plasma membrane. Basal bodies are the part that anchors the flagella to the cell.
As in other kinetoplastids, next to the axoneme is a cytoskeletal structure known as the "paraflagellar rod," which accompanies the axoneme of each flagellum from its base to its tip. Obviously, I was too lazy, so I only represented a portion of the paraflagellar rod and the axoneme of each flagellum, but to show that these structures run the entire length of the flagellum to the tip, I drew some little arrows lmao. Also, in my illustration, the 9+2 axoneme is represented such that the yellow lines are the doublets, and the central green lines are the singlets. Therefore, only two yellow doublets are visible in my illustration because it's assumed to be a longitudinal section, but in reality, there are nine peripheral doublets. Don't forget that detail, and if you don't understand me, well... I don't know, learn more about the 9+2 system of the axoneme; perhaps it's something I've already represented better in other illustrations.
There is a band of 6 to 7 microtubules that supports the flagellar pocket, the rostrum, the cytostome, and the cytopharynx, known as the "microtubule-reinforced band" or MTR. It begins near one of the basal bodies. The curvature of the MTR at the upper part of the rostrum is what shapes the preoral crest. There are also additional microtubules that run longitudinally alongside the MTR along the upper part of the cytopharynx, which Elbrächter et al. (1996) refer to as "microtubules of the rostrum" under the letter "M". To further complicate matters, the rostrum and cytostome (including the cytostome lip) are reinforced with rods and plates made of a homogeneous, electron-dense material. Elbrächter et al. (1996) designate them with the letter W, as "plates and rods, stiffening the rostrum." I have retained the same abbreviation, W, but used the term "rods and plates of the rostrum's stiffness."
Other notable structures include extrusomes, collectively known as the "battery," located on the dorsal side of the cell. They are cylindrical, measuring approximately 4 µm in length and 110 nm in diameter. I assume they serve the same purpose as extrusomes in other protists: to "fire" some substance that stuns, strikes, or attacks another nearby organism, either to "hunt" or "drive it away." I imagine that for H. phaeocysticola, it must serve to help it to prey, but I'm not sure about that. In Elbrächter et al. (1996) Fig. 7, only about 5 are represented, but the battery actually consists of many more, which I have tried to represent "behind" the 5 most visible ones, as lighter and more translucent vertical lines. I hope it is clear that there are many more than just 5.
Another cursed part of the organism is the so-called "spongioplasm," which is made up of "spongioplasmal vesicles." These are located on the ventral side and eventually surround the cytopharynx. What are they for? I don't know; Elbrächter et al. (1996) don't seem to explain it—you know I hate reading. In a glossary of protistological terms by Corliss and Lom (2002) (the file doesn't mention the d4mn year, but this other one does as a reference), it says that "spongioplasm" or "spongioma" is a specialized secretory cytoplasm, with a spongy appearance, and that it can be found near contractile vacuoles in ciliates and some flagellates.
Other notable stuff are the "hair vesicles." In Elbrächter et al. (1996) doesn't state it very clearly, but I assume that these vesicles with hairs (I assume, the rostrum hairs I mentioned earlier) are formed in the Golgi apparatus, where the proteins that make up those hairs are packaged into these vesicles and then go to the rostrum, transporting the hairs. There are also "microbody-like organelles," which the authors mention are "not frequent." Recall that in protists in general, microbodies are single-membrane bodies that contain enzymes for certain functions. There are several types of microbodies, but in H. phaeocysticola, it doesn't seem to be clear what type or nature of these microbody-like organelles are present.
The peripheral lacunae are actually, or at least that's what I've been able to understand from reading the works of Tashyreva et al. (2023), Tashyreva et al. (2022), and Prokopchuk et al. (2019), a single structure. It is then referred to as a "peripheral lacuna," but in micrographs this structure does not appear in its entirety due to the nature of the cell sections; it appears as elongated or globular fragments or "pieces," and these are called "peripheral lacunae" (plural). However, this actually refers to the sectioning of the organism, not to several separate structures. I infer this, of course, based on those articles that describe other species related to H. phaeocysticola, but in Elbrächter et al. (1996) this reality is not very clear (I would be afraid that it is not so... I don't think so). The peripheral lacuna is assumed to fulfill some osmoregulatory function, according to Prokopchuk et al. (2019). This is because when the organism is prepared for microscopy, the "pieces" ("peripheral lacunae") swell considerably.
In H. phaeocysticola, the "peripheral lacunae" are supposed to be present throughout the cell except at the apical region, extending through the cell center to the lower lip of the cytostome, but "they are absent in the flagellar pocket and over extrusomes" (Elbrächter et al. 1996). The authors mention that this gives the appearance of the cell being encased in a "cyst." From this, I imagine that the peripheral lacuna is not as branched as the mitochondrion, but rather a structure or "layer" beneath the plasma membrane, and its shape varies depending on its swelling. However, in the illustration, I haven't depicted it as a large structure "surrounding" the entire interior of the cell (except for the apical region) because... I'm not entirely sure that's the most accurate representation. In other sources, it's represented as a swollen band at the edges of the cross-section, and that's how I've depicted it. So, assume my illustration has a longitudinal section feel to it.
Well, discussing the peripheral lacuna has taken up quite a bit of my time and required a lot of redrawing, so I'm traumatized. Finally, let's move on to something I know better: the nucleus, which is located nearby, dorsally, and below the flagellar pocket. The nucleus has a nucleolus, and sometimes, the nucleolus is surrounded by dense, heterochromatic masses that are quite noticeable.
The mitochondrion is, in theory, a single, reticulated structure whose branches extend throughout the cell. The mitochondrion is of the polykinetoplast type. This means there are several kDNA "clusters" (kinetoplasts) dispersed throughout the mitochondrion. This might sound strange from a traditional teaching perspective, where kinetoplastids (like Trypanosoma) are taught to have only one kinetoplastid, usually near the basal bodies. This condition is called "eukinetoplastic." H. phaeocysticola is not eukinetoplastic; instead, it is "polykinetoplastic." There are many ways in which kDNA is distributed in kinetoplastid organisms. Be aware of this.
Finally, I must point out the existence of the Golgi apparatus, located between the cytopharynx, the lower part of the flagellar pocket, and the nucleus; the digestion vacuole, which is quite large and occupies a significant portion of the posterior space of the cell (it should be noted that this is temporary, as when the organism feeds and shortly thereafter, this vacuole is absent, replaced by small refractive granules); and the endoplasmatic reticulum, which is not actually mentioned at all in Elbrächter et al. (1996). I assume it is a branched structure that potentially extends throughout the cytoplasm, as occurs in other kinetoplastids, but I have not depicted it occupying the entire cell. Therefore, my representation of it is speculative.
I'm glad I finally finished writing about this organism. I don't think I could have put it off any longer. It's something that makes me feel a little better. I hope to share another drawing in the future.
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