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First things first: all the illustrations here are free to use for any project, research, or assignment you want under a Creative Commons CC BY-SA 4.0 license. The illustrations cannot be used for commercial purposes. And you must give credit for them. Mentioning me is enough: "DOTkamina (2026)."
Second, the sources, of course. Fortunately, I only relied on one article for the illustrations and all the written information in this post: "Dolichomastix tenuilepis sp. nov., a first insight into the microanatomy of the genus Dolichomastix (Mamiellales, Prasinophyceae, Chlorophyta)" (1997), by Jahn Throndsen and Adriana Zingone.
Additionally, I consulted "Phylogenetic position of Crustomastix stigmatica sp. nov. and Dolichomastix tenuilepis in relation to the Mamiellales (Prasinophyceae, Chlorophyta)" Zingone et al. 2002; and "Basal body structure and cell cycle-dependent biogenesis in Trypanosoma brucei" Vaughan and Gull (2015). Both works were consulted primarily to review the nature of the 9+2 arrangement of the flagellar axoneme.
First, a little taxonomy. D. tenuilepis is included in the order Dolichomastigales, this in the class Mamiellophyceae, infrakingdom Chlorophyta, which is included in the subkingdom Viridiplantae (plants and algae related to plants, with chlorophytes being an infrakingdom related to streptophytes, the group in which plants as such are included).
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| Dolichomastix tenuilepis. Main illustration. |
That said, the main illustration encompassing everything I depicted is the one that... that is above this text dude. It includes a lateral view (left side) of Dolichomastix tenuilepis, a detail of the hair scales on its flagella, a detail of the flagellar apparatus, a cross-section, dorsal and ventral views, and a detail of the eyespot, which is in tangential section. "I will describe these subsections in more detail later".
I have to say that the image makes me somewhat uneasy; on the one hand, I'm proud to think that I finally managed to finish something so complicated to depict, which was just a pencil sketch. But on the other hand, I think it's too cluttered.
I'm not sure if you can see it, but in this overall image, in the illustration corresponding to the lateral view, there's a line of yellow dots, representing the hypothetical transversal section.
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D. tenuilepis. Longitudinal or lateral (left side) view.
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The organism has a rounded-triangular shape, measuring 3 to 4.5 µm in length, with a flattened area from which the two flagella emerge. In the image, I've chosen to represent the species at 4 µm, and the flagellar length is based on this size (the scale bar is 4 µm for the lateral view of the organism, the main representation). That's all. The width and size of the organelles don't follow this scale, purely for aesthetic reasons and to make them visible. I've tried to make it as realistic as possible, but I wanted to keep this in mind.
Dolichomastix tenuilepis has only one large, pale olive-to-green chloroplast that occupies almost the entire ventral surface. It's cup-shaped and contains a single pyrenoid covered with a starch sheath; this starch sheath is also cup-shaped. This shape is due to the starch sheath not actually covering the entire pyrenoid. The area where it is absent is due to one or more peduncles extending from the pyrenoid. I haven't drawed a pedancle in the illustration (because I've basically forgotten), but that peduncle would be located in the area of the pyrenoid not covered by the starch sheath (in the illustration, in the middle of the pyrenoid located dorsally). The pyrenoid is located dorsally within the chloroplast.
On the most distal (ventral) side of the chloroplast, there is an eyespot or stigma, an organelle that acts as an eye (very primitively, detecting the direction and intensity of light). The eyespot in Dolichomastix tenuilepis is basically a layer of densely packed droplets, which have a hexagonal shape when cut tangentially. I represent this in the dorsal and ventral views shown later.
Above the chloroplast is a sausage-shaped
mitochondrion. I've depicted it that way in the image, but in reality, mitochondrion isn't necessarily straight. Therefore, in a true longitudinal section, they would appear cut. Thus, in
Throndsen and Zingone (1997), Figures 10 and 11, it appears as if there are two small, circular mitochondria at each end of the cell, but that's because in that section, only the ends of the entire mitochondrion are cut. It's very important to read the original descriptions! Throndsen and Zingone (1997) mention that the mitochondrion "follows the inner edge of the chloroplast."
Between the region where the pyrenoid of the chloroplast is located and the nucleus, there is a microbody. Microbodies are organelles that house proteins involved in some process of cellular metabolism. Examples of microbodies in other organisms are peroxisomes and glyoxysomes. In Dolichomastix tenuilepis, its microbody does not appear to have been categorized into any specific type, nor have I found (so far) any information about what type of proteins it might contain and for what function.
In my illustration, I have chosen to represent the microbody as being "behind" the mitochondria. I have done this because in
Throndsen and Zingone (1997) Figure 11, it is not very clear whether the microbody is behind or in front of the middle part of the mitochondria, but in Figure 12, which is a cross-section, the sectioned portion of the mitochondrion is located toward the left, and the nucleus toward the right.
Considering that the microbody is located "between the nucleus and the pyrenoid region in the chloroplast," this should mean that spatially it is located on the right. That is, transversely. Viewed longitudinally (laterally), from the left side of the cell, the microbody would appear to be covered or hidden by the mitochondria. Well, that's the logic I came up with.
Another organelle for which there is photographic evidence in
Dolichomastix tenuilepis is the
Golgi apparatus. It is located near the bases of the flagella (that is, near the basal bodies), and opposite the nucleus. The organism's scales are produced in the Golgi apparatus (I will explain more about them later), and these are transported to the cell surface by
scale-bearing vesicles.
Throndsen and Zingone (1997) observed an additional vesicle containing fibrous material, "which does not appear to be related to the Golgi apparatus." In the illustration, I have labeled it "
Fibrillar vesicle material."
The
nucleus would be located in the posterior region of the cell, when viewed laterally from the left side of the organism. The nucleus is surrounded by the
endoplasmic reticulum; I assume there is both rough and smooth endoplasmic reticulum (the rough endoplasmic reticulum is the one with a large number of ribosomes, which are the dots I have represented on the rough endoplasmic reticulum in the illustration). However,
Throndsen and Zingone (1997) only mention that: "A very well developed endoplasmic reticulum, continuous with the perinuclear space, is observed in some sections." See Figure 15 of the article.
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| Lateral view. No labels version. |
With that, we come to the flagella. There are two; the right one (12 to 18 µm) is always longer than the left one (8 to 16 µm). You already know the basic structure of eukaryotic flagella: a flagellum is actually a system of microtubules (called an "axoneme") that originates in the cytoplasm from microtubular structures called "basal bodies." The axoneme of each basal body then extends out of the cytoplasm, enveloped in a plasma membrane. This axoneme and surrounding plasma membrane assembly is what we call a "flagella," with the basal body serving as the point of attachment and origin. As in other eukaryotes, the microtubule arrangement of the axoneme is 9+2: nine microtubule doublets surrounding two central microtubules.
Now, the 9+2 axoneme of a flagellum is supposed to originate after the
transition zone, which is actually "the same axoneme" with a slightly different configuration (for example, 9+0, 9 microtubule doublets without microtubules in the center, as occurs in
Trypanosoma brucei) (
Vaughan and Gull 2015), and which is located more or less before the exit zone of the 9+2 axoneme in the cytoplasm. The transition zone is what connects to the basal body, which has an arrangement of 9 microtubule triplets.
In
Dolichomastix tenuilepis, I only know that the flagellar axoneme itself is 9+2 (see
Throndsen and Zingone (1997), Figure 12). I don't know the configuration of the transition zone or the basal body (although I assume it would have 9 triplets, since that is the general configuration of the basal body in eukaryotes). In the junction between the transition zone and the flagellum itself, there is a "
transitional plate," a protein structure that surrounds this junction. In
D. tenuilepis, the transitional plate can be bordered by a
double protein ring. This is represented in the "Flagellar system detail" illustration.
Another peculiarity is that, in other organisms, the flagellum should already have its 9+2 arrangement as soon as it "emerges" from the transition zone (that is, as soon as the connection delimited by the transitional plate begins). But in Dolichomastix tenuilepis, this is not the case. In fact, the central pair of microtubules of the 9+2 axoneme appears late, not immediately after the transitional plate.
The basal bodies of the flagella are described as long, and between them lies the "distal fiber," a structural protein involved in anchoring the basal bodies to the plasma membrane (Megías et al. 2025). Other notable structural protein components of basal bodies are the "flagellar roots," which anchor the basal bodies to the cell cytoplasm. I will discuss these in more detail later.
The flagella are covered by hair scales, which can be of three types: T-hair scales, lateral, 0.4 µm long, tubular in shape, arranged in two rows on each flagellum, and with an accumulation of electron-dense material at their tips, which makes the tips of the T-hair scales appear darker under an electron microscope.
At the ends of each flagellum, there are aggregates of 3 or 4 "tip hair scales," 0.3 µm long, similar in shape to the T-hair scales, except without the darker terminal end.
Finally, the third type are the P1-hairs. These are present in very small numbers (in Throndsen and Zingone (1997) Figure 25, only about four are indicated, although I could swear I see five). They are only found in the proximal part (the area closest to the cytoplasm) of the right flagellum (the longer one). They are incredibly long, measuring 1.7 µm, and consist of two parts: the proximal shaft or "first portion," measuring 1.2 µm, and the distal part or "second portion," measuring 0.5 µm if you do the math, which consists of 32 globular subunits in a chain.
This anatomy of the hair scales is truly strange. However, Dolichomastix tenuilepis has more "normal" scales (that is, scales that are not hair-like), and of two types: "body scales," which cover the plasma membrane of the cell body; and the "flagellar scales", which cover the plasma membrane of the flagella. These can be seen more clearly in the following image, "Flagellar system's close up".
In this image, I have attempted to closely depict the basal body system and how each flagellum emerges from its respective basal body. The distal fiber connecting the two basal bodies is visible. The transitional plate in each flagellum, the area between the end of the basal body and the transitional plate, would be the "transition zone." The transitional plate of the left flagellum has darker edges, corresponding to the double ring of electron-dense material, according to Throndsen and Zingone (1997) (Figure 20). I have chosen to represent it in the transitional plate of the left flagellum, but the authors mention that this double ring is more of a structure "that may or may not exist." I interpret this to mean that the double ring could very well be in the transitional plate of the right flagellum, or in both flagella simultaneously.
From the transitional plate onward, we can begin to speak of the flagellum as such, with a 9+2 axoneme. It's noticeable how this arrangement actually begins later in the flagellum, as the two central microtubules start slightly after the transitional plate (shown in yellow). I've also depicted two peripheral microtubule doublets (shown in green), a very simplified representation, but remember that in reality there are nine microtubule doublets surrounding the two central microtubules (9+2 arrangement).
A flagellar root emerges from the basal body of the left flagellum, represented as three parallel pink lines. This is one of the possible arrangements. Flagellar roots are also clusters of microtubules that anchor the basal bodies to the cytoplasm. One such arrangement is the "triple root," consisting of three parallel microtubules. If viewed longitudinally, they would appear as three parallel lines very close together, just as seen in the image... although this isn't very noticeable under a microscope. It's more evident in a transverse section, where they appear as three closely spaced points.
The other arrangement is the "three + one root," which consists of three parallel microtubules alongside a single, isolated microtubule running close to the triplet. These are the two types reported explicitly, although Throndsen and Zingone (1997), Figure 23, mention a "three + two root" arrangement, which I have also represented.
In theory, a flagellar root should emerge from each basal body, but for some reason, Throndsen and Zingone (1997) mention: "a triple or three + one microtubular root runs from the left basal body," passing beneath the distal fiber and approaching the cell surface while passing the nucleus. This implies that there is only one flagellar root corresponding to the basal body of the left flagellum, and not for the right. The authors report, however, another flagellar root near the Golgi apparatus (which I have indeed represented in the lateral view image of the organism, also as three parallel pink lines), and I believe that this would actually be the flagellar root that emerges from the basal body of the right flagellum, extending through the cytoplasm in the Golgi apparatus region. I don't know if it is also close to the cell membrane.
Finally, you can see how the body scales and flagellar scales are arranged in the plasma membrane. Note also that the body scales are more spherical and larger (0.4 µm), with 14 concentric ridges, a narrow thickened rim, and a faint knob in the middle. There are also smaller body scales of 0.3 µm that have fewer ridges, up to only 9.
The flagellar scales are more irregularly "elliptical," measuring 0.3 x 0.2 µm. They also have a narrow rim, a faint central knob, and concentric ridges, numbering 7 to 10. These body and flagellar scales have also been represented to scale alongside the detailed representations of the three types of hair scales, in the image of the side view of the organism.
This is a cross-sectional representation of Dolichomastix tenuilepis. I've more or less depicted the same parts I explained in the side view image; I don't think there's anything else to explain here.
Finally, the dorsal and ventral views of the organism, which I constructed from
Throndsen and Zingone (1997) Figure 10. In the dorsal view, note how the nucleus, mitochondrion, and microbody are "above" the chloroplast. The chloroplast encloses the pyrenoid, which is covered by the starch sheath, such that only a portion of the pyrenoid is visible because it is not covered by the starch sheath (the pyrenoid peduncle emerges from this area).
The
eyespot would be located on the ventral side of the chloroplast. It is not visible in the dorsal view, but it is visible in the ventral view, appearing as a small dark spot. A close-up of the droplets that make up the single layer of the eyespot, or stigma, is included. The shape of the droplets is almost a direct copycat of
Throndsen and Zingone (1997) Figure 18.
In the ventral view, note also that the chloroplast now appears to be "on top" of the other organelles, although it is actually the other way around. In that view, only the starch sheath is visible; the pyrenoid is enclosed, of course, but the area free of the starch sheath is not visible because it is located dorsally. The microbody is located between the dorsal area of the pyrenoid and the nucleus, so in this ventral view representation, it is hidden by the starch sheath of the pyrenoid.
Well, I really don't have anything else to say, except that I almost gave up on doing these illustrations because it was so complicated to read through the whole mess of Throndsen and Zingone's work (1997). I also fell asleep several times while writing this post; I hope I haven't written anything inappropriate.
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