Monomastix opisthostigma Scherffel 1912

So... how did I decide to draw this species?

Who knows? I remember considering doing something related to Paramastix conifera, an organism I'd illustrated before.

First of all, the illustrations here are free to use, and are also available on Wikimedia Commons, Creative Commons CC BY-SA 4.0 Attribution-ShareAlike 4.0 International license: you can use them freely, as long as it is not for commercial purposes (using them for commercial purposes is strictly prohibited, unless it is for a documentary, in any case you should contact me), and you must also attribute the authorship (like "DOTkamina 2026". Help me leave my mark!).

Monomastix opisthostigma is a strange organism. There isn't much information available about it; in fact, what's online is mostly reposted. Fortunately, I think it's almost enough to create the illustration.

First, I'll start with the sources used for the general cell body:

• "An image-based key: Monomastix (Chlorophyceae)". PhicoKey, A. L. Baker, 2017.
• "Chlorophya. Prasinophyta. Ulvophyceae". Katedra botaniky Přírodovědecké fakulty Univerzity Karlovy (KBPFUK) n.d.
• "Flagellate green algae from four water bodies in the state of Rio de Janeiro, Southeast Brazil". Mariângela Menezes and Carlos Eduardo de Mattos Bicudo. Hoehnea, 2008.
• "Monomastix Scherffel, 1912". AlgaeBase, 2013.
• "Monomastix minuta and M. opisthostigma (Chlorophyta, Prasinophyceae), two species new to polish flora". Joanna Picińska-Fałtynowicz. Polish Botanical Journal 48(1): 79-81. 2003.
• "Monomastix opisthostigma". Protist Information Server: images by Y. Tsukii 1998.
• "Monomastix opisthostigma". Protist Information Server: Protist Movies. 2007. 
• "Monomastix opisthostigma Scherffel 1912". AlgaeBase, 2020.

So, based on those sources, I also wrote the following, which you will see in this post: Monomastix belongs to the family Monomastigaceae, class Mamiellophyceae, phylum Chlorophyta, which in turn is included in the subkingdom Viridiplantae. This means that Monomastix is ​​included in the large group of organisms considered "plants and green algae sensu stricto" (green plants and green algae in the strict sense). 

Phylogenetically, Chlorophyta is related to other clades of Viridiplantae (Prasinococcus, Mesostigmatophyceae, Chara, etc.) which are then "distantly" related to the clade Embryophytes, the "land plants sensu stricto" as such... plants, that is. Chlorophyta (and therefore Monomastix) is the Viridiplantae clade most distantly related to land plants. Although included within Viridiplantae, it is closely related to the ancestor that gave rise to the clade, as well as the other two Viridiplantae relatives (the red algae, Rhodophyta, and Glaucophyta), which together with Viridiplantae make up the Archaeplastida clade.

Monomastix opisthostigma has several characteristics that can vary depending on the individual. It is described as having an ellipsoidal or nearly cylindrical to elongated shape, a slightly asymmetrical cell body with rounded ends (anterior and posterior), and a slightly inclined horizontal position. I'm not sure if this last point is related to the fact that, in the Protist Information Server micrographs, one end (the anterior) appears wider than the posterior. This differs from the schematic illustrations in Picińska-Fałtynowicz (2003) and Menezes and Bicudo (2008) (Figures 106-112), where the organism appears almost perfectly oval, and I would swear wider than it actually is. I have chosen to represent it as if the anterior end were slightly enlarged.

Note that the median trichocyst measures aprox. 4 µm in the illustration (that is an artistical decision). The size of M. opisthostigma can range from 14 to 21 µm in width and 6 to 10 µm in length. In Menezes and Bicudo (2008), it is mentioned that "there are usually two chloroplasts, sometimes one," but elsewhere I see that they refer to a single chloroplast, which, at the back of the cell, has a deep vertical incision... this means that a chloroplast is actually made up of two lobes connected by a junction at the back of the cell, of varying narrowness. I suppose that when this narrowing is so extreme, or doesn't exist at all, they refer to two chloroplasts as such.

Each chloroplast lobe has a pyrenoid in its middle, which I assume is covered in a starch sheath, as I infer from Menezes and Bicudo (2008) (Figures 106-112). An elliptical stigma may (or may not) be present at the back. The stigma is a structure that acts as an eye. Picińska-Fałtynowicz (2003) mentions that the stigma (or "eyespot") is red.

At the apical (anterior) end of the cell, there is a slight depression or indentation, easily visible in the drawing as a slight concave curve. There should be a groove there (which I haven't shown) from which the organism's single flagellum emerges. This flagellum is thin and tends to become thinner towards its tip. The flagellum may be attached to a "pro-basal body," as described in Protist Movies (2007). This is odd because I would expect flagella to have a basal body to anchor them. The "pro-basal body" is implied to be a simpler or "preceding" structure of the basal body, and it's also indicated with a question mark. Mysterious...

In the anterior portion, there is generally a single contractile vacuole; rarely, there may be two. The nucleus is also located anteriorly, though not as apically. Trichocysts are thought to act as a defense mechanism in other organisms: they are a type of extrusome (the ejectisomes of cryptomonads are also extrusomes) that release a kind of fibrous protein cords grouped into a spindle-like structure, which serves to damage or attack a potential predator. I would believe that the trichocysts of Monomastix do the same thing. When the cells are juveniles, they have one or two. Later, they can have three or four. According to Baker (2017) and Protist Movies (2007), up to seven. The trichocysts are elongated, 3 to 5 µm long, located parallel to each other, and sometimes absent according to Menezes and Bicudo (2008).

The endoplasmic reticulum, Golgi apparatus, and mitochondrion are depicted near the nucleus, and their shapes and sizes are purely speculative; they are assumed to exist, as in almost any standard eukaryotic cell. In the rough endoplasmic reticulum, you will see many dots; these are the ribosomes concentrated in that structure. Additionally, several ribosomes are distributed throughout the cell in the illustration, as they should be in real life for any eukaryotic cell.

I have chosen to depict only one mitochondrion, but I don't know if there might be more; I haven't found any information on this. What I have found is that there is a single mitochondrion in other species related to M. opisthostigma, which are also included in the class Mamiellophyceae: Crustomastix didyma (Nakayama et al. 2000), Ostreococcus tauri (Joux et al. 2015), and Dolichomastix tenuilepis (Throndsen et al. 1997). Since they are included in the same class as Monomastix, I assume that M. opisthostigma could also have a single mitochondrion. You will also see that I have represented the mitochondrial cristae as if they were tubular, but that is also speculative.

This drawing can be considered part of the end of a phase. I finally blocked it out (girl M). There was no point in clinging to any more illusions.

ミヽ（。＞＜）ノ

Cryptomonas obovata Skuja 1948... and notes on Cryptomonas morphs

Well, I don't expect to have much to say about this one, to be honest, except that I've noticed some details that were perhaps missing from the other Cryptomonas curvata illustration I published back in 2025. Damn, that year sounds so far away, and it's already February 2026. When will it be Christmas again?

The following illustrations depict Cryptomonas obovata Skuja 1948, 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.

There are two main sources I used as a basis for creating the illustration of this organism:

• "Cryptomonas obovata Skuja, 1948". Martin Kreutz, 2021. Real Micro Life.
• "Chapter 18 - Cryptomonads". Brec L. Clay, 2015. Freshwater Algae of North America (Second Edition). Academic Press.

Btw, that chapter of "Cryptomonads" is even haunting my dreams. Clay, Lee, Hill, Andersen, Kugrens etc., seem to be the experts on cryptomonad algae; they've been researching these organisms since the past century (That's an exaggeration, but... well, you know what I mean). It would fill me with uncertainty, humility, joy, and a touch of fear if they were to see the images I create.

For the design of the flagella, I relied on this article: "Ultrastructural variations in cryptomonad flagella", by Paul Kugrens, Robert E. Lee, Robert A. Andersen, 1987. The design of the mitochondrion is speculative, but it is based on what is said in Santore and Greenwood (1977). I will explain it later.

Cryptomonas obovata follows a similar anatomical scheme to that of Cryptomonas curvata, which I illustrated earlier. The first noticeable difference is in its shape: Cryptomonas curvata could be oval-shaped but slightly more elongated than C. obovata, in addition to having a slight curve at its posterior end.

The second difference, and the one I find most unnerving, is the absence of pyrenoids. Instead, it has numerous starch granules distributed throughout the cell, although Kreutz (2021) mentions that these are located "beneath the chloroplasts." In microscopic photographs (see Kreutz (2021): Figures 1 to 4), these starch granules are clearly visible in both ventral and dorsal views. In my representation, I have chosen to depict them as being beneath the chloroplasts—in other words, "covered" or "hidden" by them. But you should consider that in real life, this property wouldn't be so obvious. Let's not forget that C. obovata has two chloroplasts.

There's another important aspect I should mention: some species within the genus Cryptomonas, according to Clay (2015), can have two distinct morphotypes in their life cycles: the cryptomorph and the campylomorph. I'd say this is a bit poorly worded, because at first glance it implies that it occurs "in all Cryptomonas species," but a quick review of the article by Hoef-Emden and Melkonian (2003) shows that this isn't always the case. Some species do indeed exhibit both morphotypes (cryptomorph or campylomorph), while other species only express one of the two (or, based on current research, it's assumed that only one morphotype occurs in these species because the other simply hasn't been found or observed).

So, briefly, using Clay's (2015) description: the cryptomorph consists of cells that are more or less rounded or oval in shape. These cells are protected by the periplast (a structure that performs a function similar to that of the cell wall in plant cells). The periplast has two layers: the inner periplast component (which in the cryptomorph consists of rounded or oval plates), and the surface periplast component (which in the cryptomorph is made of a thin layer of fibrils).

In the cryptomorph, the plastidial complex (the set of cellular plastids) is generally made up of two chloroplasts, with two pyrenoids not traversed by thylakoids, and two nucleomorphs, one between the nucleus and the pyrenoids. The furrow of the cryptomorph is "complex," possessing a stoma.

The campylomorph was considered for some time to be such a distinct morph that individuals with this morph were considered species in different genera of Cryptomonas. Formally, Campylomonas and Chilomonas. Now that it's known that the forms of both genera are actually the campylomorph, an alternative to the cryptomorph of Cryptomonas, they are considered synonymous where applicable.

But let's see: using again Clay (2015): the campylomorph is first different from the cryptomorph by having a more "sigmoid" cell shape; I would describe it, in simple terms, as a somewhat oval, flattened cell shape with varying degrees of elongation and curvature. More importantly, the periplast may be composed solely of the inner periplast component, simply a layer without shaped plates. The surface periplast component may be absent, but if present, it would be made of fibrillar material or heptagonal "scales."

The campylomorph generally has the same plastidial complex structure as the cryptomorph. The most noticeable difference is seen in the furrow, which lacks a stoma. In addition, it also has a scalariform furrow plate, a structure similar to the furrow plate that, in the campilomorph, resembles a ladder. In the cryptomorph, this furrow plate is only fibrous. I haven't depicted the furrow plate in the illustrations of this species. Finally, the vestibulum in the campylomorph also has a "vestibular ligule," a kind of extension that covers a small portion of the vestibule.

My state right now.

But anyway, those would be the main differences between the cryptomorph and the campylomorph of a Cryptomonas species. Now, in which species exactly, and in which ones only a single morph has been observed... hell, who knows?

According to the article by Hoef-Emden and Melkonian (2003), and comparing it with the information in Clay (2015), the cryptomonad species in which only the cryptomorph was found are: C. ovata, C. obovata (the species I illustrated in this post), C. phaseolus, C. tetrapyrenoidosa, and C. erosa. Clay (2015) also mentions C. ozolinii Skuja 1939 as a cryptomorph, but Hoef-Emden and Melkonian (2003) already indicate that it is actually a synonym of C. pyrenoidifera Geitler 1922 emend. Hoef-Emden and Melkonian (in Hoef-Emden and Melkonian (2003), this synonym is written simply as "C. ozolini Skuja"). C. pyrenoidifera exhibits both morphs, cryptomorph and campylomorph.

Similarly, considering Hoef-Emden and Melkonian (2003) and Clay (2015), the species where, conversely, only the campylomorph was found are: C. platyuris and C. marssonii. Clay (2015) also mentions C. rostratiformis Skuja (omitting the "1950"), which would actually be a synonym of C. curvata Ehrenberg 1832. I had illustrated C. curvata as campylomorphic, but according to Hoef-Emden and Melkonian (2003), it also has the cryptomorph.

There is a problem with C. reflexa. First, it should be noted that Clay (2015) mentions C. reflexa Marsson (syn. Campylomonas reflexa Hill). In AlgaeBase, the closest taxon to the one mentioned is C. reflexa (M.Marsson) Skuja 1939, but I'm not certain. Hoef-Emden and Melkonian (2003) mention C. reflexa Skuja (1939), which may in fact be the same as C. reflexa (M.Marsson) Skuja 1939 in AlgaeBase (they also appear in the same original publication). In any case, Hoef-Emden and Melkonian (2003) indicate C. reflexa as another synonym of C. curvata, and therefore, it would have both cryptomorph and campylomorph. C. reflexa has about five names in AlgaeBase, and all of them are in an "unstable" state, meaning they are not fully accepted.

C. marssonii Skuja 1948 does have only a campylomorph (or rather, only that morph has been found), according to Hoef-Emden and Melkonian (2003). The problem is that this name is currently being debated...

But anyway. I think that covers the important points regarding the morphs.

Returning to Cryptomonas obovata, it's established that it only has the cryptomorph. Based on the general characteristics of the cryptomorph, I have represented its furrow with a stoma. The vestibule lacks a vestibular ligule. There are two nucleomorphs, one on each side of the nucleus.

The main difference from the general scheme of the cryptomorph is that C. obovata does not have pyrenoids; instead, it has those starch granules I mentioned earlier. The ejectisomes "envelop" the entire gullet. This is something that also occurs in other Cryptomonas species. I mention this because in the illustration of C. curvata I did some time ago, I didn't depict the ejectisomes surrounding the entire gullet. Why? For better visibility... I suppose. The contractile vacuole is located behind the chloroplasts and near the anterior region, according to what I see in Kreutz (2021). I haven't represented the periplast and its components.

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.

Finally, the flagella of C. obovata are of type 1 flagella according to Kugrens et al. (1987): the long (dorsal) flagellum has two opposing rows of mastigonemes, each with a single terminal filament. The short (ventral) flagellum also has a single row of mastigonemes, each with two terminal filaments of different lengths. Additionally, there are approximately three terminal hairs at the end of the dorsal flagellum.

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 could swear there was more to say, but the truth is I went off for a while to... I don't know, do something, the thing is I don't remember anymore. I hope I've covered everything.

Oh right, I almost forgot... the maupas bodies! Those two funny things way behind the chloroplasts and starch granules. C. obovata only has two maupas bodies. I don't know if you know this, but all the colors in these drawings are merely schematic and for educational purposes, and don't necessarily correspond to what you can see in real life. However, according to the images in Kreutz (2021), maupas bodies can be seen under a microscope as two shiny structures. What are they for? .... HAH, who knows?