Microstomum rogozini sp. n. (Plathelminthes, Dolichomicrostomida, Microstomidae) from Lake Baikal

An illustrated description of Microstomum rogozini sp. n. is given based on original material collected over the period of 1994–2008; it can be concluded that this new species is the most common and most numerous representative of microstomids that inhabit Lake Baikal. Individuals of this species are bright orange and transparent and consist of one–two zooids; in the mature state, they have a solid spirally twisted stylet with 3.5 whorls. Its length ranges from 120 to 170 µm at an average value of about 145 µm. The distal opening is slit-shaped and is located on the distal half-whorl. Comparisons, as well as the distribution, variability, and ecology of this species, are also given.