Short answers, pulled from the story.
Cryptomonads, also called cryptophytes, are a superclass of single-celled algae and colorless flagellates. Each cell is around 10-50 micrometres in size. They are common in freshwater habitats and also occur in marine and brackish environments.
Cryptomonad chloroplasts are surrounded by four membranes because they were acquired through secondary endosymbiosis: an ancestral host engulfed a red alga, whose own double membrane was retained alongside the host's membrane layers. A remnant nucleus called the nucleomorph sits between the inner two membranes.
The nucleomorph is a reduced cell nucleus found between the middle two membranes of the cryptomonad chloroplast. It is the vestigial nucleus of the red alga that was engulfed during secondary endosymbiosis, confirmed by genetic studies.
Ejectisomes are coiled extrusomes made of two connected spiral ribbons held under tension. When a cryptomonad is disturbed by mechanical, chemical, or light stress, the ejectisomes discharge and propel the cell away in a zig-zag course.
Christian Gottfried Ehrenberg made the first recorded mention of cryptomonads in 1831 while studying Infusoria. Later, botanists classified them as the algae division Cryptophyta while zoologists placed them in the protozoan order Cryptomonadina.
The sister group to the cryptomonads is most likely the kathablepharids, a group of flagellates that also possess ejectisomes. Molecular studies by Parfrey and Burki placed Cryptophyceae as a sister clade to the green algae, or to green algae plus glaucophytes.