KINGDOM PROTISTA - Division Euglenophyta
When science was young, and there were only two kingdoms (Plantae and Animalia), euglenoids presented such an enigma that they were treated as plants in botany texts and as animals in zoology texts. 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. Beside the single, locomotory flagellum is a photosensitive red "eyespot," or stigma, which aids the organism in orienting itself towards light--a useful trait if you're photosynthetic!
The remaining two-thirds of euglenoids are either facultatively or, like animals, fully heterotrophic. They seem to bear greater resemblance to the mastigophoran protozoans (whom you'll meet later this semester) than to algae. 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. Multiply they do, however, and with fierce efficiency! 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.
But if euglenoids don't have sex, how did so many species evolve? It is a mystery, perhaps a holdover from a time when genetic recombination did occur among them.
