A new species of the genus Myostenostomum (Platyhelminthes: Catenulida: Stenostomidae) from Lake Bile (Ukraine).

A new species of freshwater catenulids, Myostenostomum styrensis sp. nov., is described from karst-glacial Lake Bile (Rivne Region, Ukraine). The morphology description and illustrations are provided. Myostenostomum styrensis sp. nov. is distinguished from its congeners by the following combination of characters: the pharynx is complicated and divided into two parts (the oral part and the esophageal part), the anterior brain lobes are deeply dented, the basal parts of the anterior brain lobes are significantly elongated, the posterior lobes and transverse commissure are fused, forming an arcuate ganglion with folded lateral prolongations, pharyngeal glands with long stalks extend from the upper part of the intestine and open at the anterior margin of the pharynx, light-refracting bodies are absent, there are large well-defined ciliated pits, and a well-defined cauda.