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Euglena is a genus of single cell flagellate eukaryotes. It is the best known and most widely studied member of the class Euglenoidea, a diverse group containing some 54 genera and at least 200 species. [1] [2] Species of Euglena are found in fresh water and salt water.
Euglena gracilis is a freshwater species of single-celled alga in the genus Euglena. It has secondary chloroplasts, and is a mixotroph able to feed by photosynthesis or phagocytosis. It has a highly flexible cell surface, allowing it to change shape from a thin cell up to 100 μm long to a sphere of approximately 20 μm.
Unlike the green euglenids, they lack both an eyespot (stigma), and the paraflagellar body (photoreceptor) that is normally coupled with that organelle. [3] However, while Peranema lack a localized photoreceptor, they do possess the light-sensitive protein rhodopsin , and respond to changes in light with a characteristic "curling behaviour."
They are insufficient for vision, as they cannot distinguish shapes or determine the direction light is coming from. Eyespots are found in nearly all major animal groups, and are common among unicellular organisms, including euglena. The euglena's eyespot, called a stigma, is located at its anterior end. It is a small splotch of red pigment ...
The stigma is located laterally, in a fixed plane relative to the cilia, but not directly adjacent to the basal bodies. [42] [43] The fixed position is ensured by the attachment of the chloroplast to one of the ciliary roots. [44] The pigmented stigma is not to be confused with the photoreceptor.
The stigma is located laterally, in a fixed plane relative to the cilia, but not directly adjacent to the basal bodies. [62] [63] The fixed position is ensured by the attachment of the chloroplast to one of the ciliary roots. [64] The pigmented stigma is not to be confused with the photoreceptor.
Euglenales consists mostly of freshwater organisms, in contrast to its sister Eutreptiales which is generally marine. Cells have two flagella, but only one is emergent; the other is very short and does not emerge from the cell, so cells appear to have only one flagellum. [3]
The stigma, together with the style and ovary (typically called the stigma-style-ovary system) comprises the pistil, which is part of the gynoecium or female reproductive organ of a plant. The stigma itself forms the distal portion of the style, or stylodia, and is composed of stigmatic papillae , the cells of which are receptive to pollen.