Cryptomonas paramaecium (Ehrenberg) Hoef-Emden & Melkonian 2003 = Chilomonas paramaecium Ehrenberg 1831

This organism is a hoax. It has supposedly already been reclassified as another species of Cryptomonas campylomorph form (no cryptomorph has been found), but in any case, AlgaeBase still considers it the type (lectotype) of the genus Chilomonas, since it was previously considered part of that genus, different from Cryptomonas. There is another name used, which is "Chilomonas paramecium", instead of "paramaecium". It appears as such in Clay (2015).

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 paramaecium is another distant relative of plant ancestors.

Reminder that it is free to use under CC BY-SA 4.0, non-commercial, attribution required (DOTkamina 2026). The sources I used and read for the creation of the image, as well as the text where I explain, are these:

• "Chapter 18 - Cryptomonads". Brec L. Clay, 2015. Freshwater Algae of North America (Second Edition). Academic Press.
• "Cryptomonas paramaecium (Ehrenberg, 1832) Hoef-Emden & Melkonian, 2003". Martin Kreutz. Real Micro Life 2021.
• "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.

As I mentioned, C. paramaecium has a campylomorph form. This means a simple furrow without stomata and an almost sigmoid cell shape, although in this species, the shape is usually more ovate-elongated and slightly wider anteriorly. The vestibulum has a vestibular ligule (this ligule is absent in the cryptomorph form in another species). The furrow is quite small compared to others.

Most notably, it lacks chloroplasts and pyrenoids, instead possessing leucoplasts with starch grains and nucleomorphs (one in each chloroplast). Therefore, it doesn't have a red or green pigment to give it color; it is transparent (though under a microscope it appears grayish or glassy). In this image, I've used various grayish to bluish tones and other minor colors, but it's important to remember that the objective is more didactic than realistic.

Dimensions: 14–28 µm long × 10–13 µm wide × 8–10 µm thick. However, Clay (2015) attributes larger sizes to it, 20–40 µm long and 10–20 µm in diameter.

Other observed features include the contractile vacuole at the anterior extreme of the cell, two Maupas bodies located approximately in the cell's central region, and the gullet surrounded by ejectisomes (few are illustrated in Clay (2015), but more are seen in the micrographs by Kreutz (2021).

According to Kreutz (2021), flagella are slightly shorter than the cell and the same length, but in the illustrations from both that source and Clay (2015), they are depicted as shorter relative to the cell, and I have represented them accordingly, choosing to make them approximately half the size of the cell. Although both are equal in length (again, in the illustrations in Kreutz (2021) and Clay (2015), they are not depicted at the same lengths), I have chosen to represent the longer flagellum slightly longer than the shorter (ventral) one.

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.

According to Kugrens et al. (1987): unlike other species, 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".

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 have nothing more to say in this post about this organism. In theory, this was supposed to be the entry about Giardia duodenalis, but I had some anatomical questions about its microtubules and I'm investigating it to see if I need to make any further corrections. 

Anyway, that's how, with this organism, I've reached illustration number 20 out of the 100 I have to complete. But hey. It's more fun to say I'm 80 short than 96.