(Authorities Note: The genus was first named in 1830, but was not diagnosed
until 1838.)
Ehrenberg, C. G. 1830. Neue Beobachtungen uber blutartige Ercheinungnenin
Aegypten, Arabien, und Sibirien, nebst einer Uebersicht und Kritik der fruher
bekannten. Annalen der Physik 18:477-514.
Ehrenberg, C. G. 1838. Die Infusionsthierchen als vollkommene Organismen.
Leipzig:Verlag von Leopold Voss.
Diagnosis:
Green, phototrophic chloroplast containing cells.
The chloroplasts may be discoid, shield-shaped or ribbon-shaped, entire
or dissected, with or without pyrenoids. Pyrenoids may be naked,or sheathed
with one or two (double-sheathed) paramylon grains. Each chloroplast type
is characteristic of a particular group of species. An
eyespot is present at the anterior of the cell independent of the chloroplast.
A paraflagellar body is present on the portion of the flagellum located
in the reservoir. The flagellum emerges from the canal/reservoir complex
subapically.The paraflagellar body is positioned adjacent to the eyespot.
Cells are never completely rigid, but show some level of euglenoid movement
(metaboly) ranging from slight to extreme.The cell body is asymmetrical
and may be somewhat flattened. Cells usually have a single emergent flagellum,
but in some species the flagellum is so short that it is not detectable
with the light microscope. A second non-emergent flagellum is present in
the reservoir. Never more than one active flagellum is present. A contractile
vacuole is present in both marine and freshwater forms and expels into the
reservoir. There tends to be much variation in shape, metaboly, chloroplasts
and pyrenoids, and flagellar length among the species making identification
difficult and many descriptions suspect.
