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.
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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.
