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Cryptomonad

life science Maturity 11-13 Next article →

Cryptomonads, also known as cryptophytes, are a unique superclass of organisms.

CSIRO ScienceImage 7234 microalgal cultures
CSIRO ScienceImage 7234 microalgal cultures

They include both algae and colorless flagellates. Most members of this group possess plastids, which are specialized parts used for energy. These tiny cells live in many different environments. They are common in freshwater habitats. They also live in marine and brackish waters. Understanding cryptomonads helps scientists learn about the history of life on Earth.

Each individual cryptomonad cell is quite small. They typically measure between 10 and 50 micrometers in size. The cells have a flattened shape. They also feature an anterior groove, which is a small pocket on the front side.

CSIRO ScienceImage 6743 SEM Cryptophyte
CSIRO ScienceImage 6743 SEM Cryptophyte

Usually, two slightly unequal flagella grow from the edge of this pocket. These flagella are covered in bipartite hairs called mastigonemes. These hairs are formed inside the endoplasmic reticulum. They are then transported to the cell surface to help the organism move.

Cryptomonads have a very specific way to react to their environment. They possess specialized structures called ejectisomes. These are a type of extrusome, or a structure used for discharging material. Ejectisomes consist of two connected spiral ribbons held under tension.

2023 Cryptomonad
2023 Cryptomonad

If the cell experiences mechanical, chemical, or light stress, these ribbons discharge. This sudden release propels the cell in a zig-zag course. This movement allows the cell to move away from a disturbance. Large ejectisomes are found near the pocket. Smaller ones are located underneath the periplast. The periplast is a specific cell covering unique to cryptophytes.

Scientists divide the superclass Cryptomonada into two distinct classes. The first class is Goniomonadea, which are heterotrophic. This means they do not make their own food. They also lack plastids entirely. The second class is Cryptophyceae, which are phototrophic. These organisms use light for energy. Both classes share three morphological characteristics. They all have a periplast. They all have ejectisomes with a secondary scroll. Finally, they all have mitochondrial cristae with flat tubules.

Many cryptomonads in the Cryptophyceae class have one or two chloroplasts. These chloroplasts contain chlorophylls a and c. They also contain phycobiliproteins, which are pigments that help capture light. Because of these pigments, the cells can appear brown, red, or blueish-green. The structure of these chloroplasts is very complex. Each one is surrounded by four membranes. There is also a reduced cell nucleus called a nucleomorph located between the middle two membranes.

2023 Cryptomonad
2023 Cryptomonad

This nucleomorph shows that the plastid likely came from a eukaryotic symbiont, specifically a red alga.

History shows that our understanding of these organisms has changed over time. Christian Gottfried Ehrenberg first mentioned cryptomonads in 1831. He was studying organisms known as infusoria. Later, different groups of scientists disagreed on how to classify them. Botanists viewed them as a division of algae called Cryptophyta. Zoologists viewed them as a group of flagellate protozoa. Some researchers even grouped them with dinoflagellates due to similar pigmentation. Today, molecular evidence suggests cryptomonads may have been primitively heterotrophic and later acquired chloroplasts.

Cryptomonads are important for studying how different groups of life are related. Genetic studies from 1994 supported the link between Goniomonas and Cryptophyceae. Some researchers placed Cryptophyceae as a sister clade to green algae. Other studies suggest their closest relatives are the kathablepharids. These are also flagellates that possess ejectisomes. By studying the DNA and structures of cryptomonads, scientists can map the complex branches of the tree of life.

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File:2023 Cryptomonad.svg
2023 Cryptomonad.svg
File:CSIRO ScienceImage 6743 SEM Cryptophyte.jpg
CSIRO ScienceImage 6743 SEM Cryptophyte.jpg
File:CSIRO ScienceImage 7234 microalgal cultures.jpg
CSIRO ScienceImage 7234 microalgal cultures.jpg
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