First Data on Microturbellarians (Plathelminthes, Rhabditophora) from Boguchansky Reservoir: 1. Kalyptorhynchia of Baikal Origin with a Description of Three New Species

This series of reports is devoted to taxonomic studies of the microturbellarian fauna (Plathelminthes, Rhabditophora) of Boguchansky Reservoir (lower part of the Angara River, Eastern Siberia). This first communication provides data on ten species of Kalyptorhynchia (Rhynchokarlingiidae), previously described from Lake Baikal. Three of them have proven to be new to science. For the six known Kalyptorhynchian species (Linella hamolaminae Timoshkin et Krivorotkin 2022, Mariareuterella baeckmanae (Timoshkin 1986), Opisthocystis curvistylus Timoshkin 1986, Rhynchokarlingia zemskayae Timoshkin 2004, Riedelella dmitrievae Timoshkin 2004, and Riedelella kravtsovae Timoshkin 2004), these finds are the first outside Baikal. The new species of Kalyptorhynchia belong to the genera Mariareuterella Timoshkin & Grygier 2005, Riedelella Timoshkin 2004, and Rhynchokarlingia Timoshkin et Mamkaev 2004. A species with five cuticular hooks in the male copulatory apparatus has been discovered for the first time. This has made it possible to expand the diagnosis of the genus Rhynchokarlingia. All the species were found in the lower reaches of the Angara River. Rhynchokarlingiidae are an autochthonous family of kalyptorhynchian worms for Baikal; it is logical to assume that all the newly described species are also of Baikal origin. Individuals of the Baikal endemic Kalyptorhynchia have been found very far from the Lake Baikal area (about 1400 km) for the first time. Our finds significantly expand the range of Rhynchokarlingiidae and Boguchansky Reservoir of the Angara should be considered as the northern range of their distribution. Illustrated descriptions of the new species are given, and differential diagnoses and data on their distribution are provided. The morphology of individuals of the subendemic Kalyptorhynchia species is described briefly; their comparison with Baikal representatives and data on their distribution are summarized.