Like plants, about a third of euglenoid species have chloroplasts containing chlorophyll a as the primary photosynthetic pigment and chlorophyll b and carotenoids as accessory pigments. A single pyrenoid, a proteinaceous body within each chloroplast, contains the enzymes necessary for the synthesis of starch from photosynthetically manufactured sugars. Pyrenoids are found only in certain algae and in very primitive plants called liverworts. The remaining two-thirds of euglenoids are either facultatively or, like animals, fully heterotrophic. It's clear that only with techniques such as rRNA and DNA sequencing can we begin to understand the complex evolutionary relationships of protist divisions, which diverged from one another so very long ago.
Euglenoids multiply via mitosis, and have never been observed to reproduce sexually.
The pea soup seen in abandoned swimming pools and stagnant ponds is most often due to a high concentration of euglenoids, all produced via mitosis. It is a mystery, perhaps a holdover from a time when genetic recombination did occur among them. In the absence of light, euglenoids lose their chloroplasts and become heterotrophic, ingesting other microorganisms to obtain organic nutrients. Organisms which can switch between autotrophic and heterotrophic nutritional modes are known as mixotrophs . This handsome, rounded euglenoid exhibits the dense chloroplast population and striking eyespot characteristic of members of this Phylum.