The members of the genus Euglena are microscopic, single-celled eukaryotes that can be found in large numbers in both marine and freshwater habitats worldwide. Exactly what they are, taxonomically speaking, has been the subject of extensive debate: like plants, their bodies contain chloroplasts filled with large amounts of the green pigment chlorophyll which allows them to absorb sunlight and carry out photosynthesis to sustain themselves, but like animals, they are capable of “eating” (when faced with low light levels that impair their ability to carry out photosynthesis they can secrete enzymes that break down dead organic matter in the water around them, allowing them to absorb nutrients from this matter through their cell membranes), moving (with a pair of tiny tail-like structures, known as flagella, allowing them to swim towards food and away from predators such as larger single-celled organisms and tiny animals such as rotifers and fish larvae) and rudimentary “seeing” (with a single redish-orange “eye spot” filtering sunlight onto a light-sensitive structure at the base of the flagella and thereby forming something comparable to a very basic eye, allowing Euglena species to distinguish between light and dark and move towards sunlight.) As such, most authorities now classify Euglena and its relatives as protists, a sort of “miscellaneous” category that includes all eukaryotic organisms that are not animals, plants or fungi. When faced with dry conditions or a lack of sunlight and food, Euglena species can encase themselves in a protective membrane and enter a dormant state until they encounter preferable conditions, and when conditions are ideal they reproduce through binary fission, a form of asexual reproduction in which a single-celled organism essentially makes a copy of its genetic material, separates these two copies at opposite ends of its body and then splits into two distinct but genetically identical individuals. When sunlight is intense and water is abundant, these organisms may reproduce so frequently that the water they live in begins to appear green (or, in the case of the species Euglena sanguinea which uniquely possesses a protective casing of the reddish substance astaxanthin around its chloroplasts to protect them from damage from intense UV radiation, red.)
(Note - on the individual pictured above, the orange mark near the top of the image is the eye spot. The flagella are tiny and transparent so are very hard to see through most microscopes, but they’re there - I promise!)
Not an animal per say, but a poster I was given for Christmas had these little goopy guys on it and I wanted to learn more about them. I think they’re cool, and while they’re not easily visible protists are still wildlife!
