Vol 102, No 11 (2023)

This is the second contribution in series devoted to the study of the microturbellarian fauna (Plathelminthes, Rhabditophora) of the Boguchansky Reservoir, lower section of the Angara River, eastern Siberia. It provides information on the taxonomy, the structure of the male copulatory organ, and zoogeography of one species each from the families Provorticidae Beklemischev 1927, Macrostomidae Benden 1870, and Microstomidae Luther 1907. The faunas of these worms in the Angara River and Lake Baikal are still poorly studied. Three species from these families were recorded and described more than 90 years ago from the Angara River before our study, but the original descriptions were accompanied by highly schematic and non-informative sketches which do not allow us to perform exact species identifications and comparisons, as a rule. In the research process of the lower section of the Angara River, we found representatives of further three species: Macrostomum johni Young 1972, Microstomum rogozini Timoshkin et Krivorotkin 2023, and Baicalellia nasonovi Timoshkin et Krivorotkin, sp. n. The stylets of M. johni from the Angara River and Lake Baikal were revealed to be almost identical in structure and size to those of specimens of the type series from Great Britain. M. rogozini is one of the most common species of Microstomidae that inhabits the coastal zone of Lake Baikal. The stylet structure of Baicalellia species resembles that of Baicalellia baicali Nasonov 1930 and Baicalellia nigrofasciata Nasonov 1930, but their available descriptions do not allow us to make reliable comparisons with the species found. Therefore, we propose to consider both these names as nomina nuda and attribute those individuals to B. nasonovi, a species new to science. Despite rhe significant geographic isolation, the stylets of Baikal and Boguchan specimens are identical in structure and size. Similarly to Kalyptorhynchian species (see contribution 1), the discovery of provorticids and microstomids of Baikal origins in such a remote section of the Angara River considerably expands their distributions and demonstrates their capacities to colonize water bodies hydrographically connected to Lake Baikal. Illustrated descriptions of Boguchan and Baikal specimens of M. johni, M. rogozini and B. nasonovi, comparisons with the most similar species and zoogeographic information are given. In addition, a complete checklist of the Angara River microturbellarian fauna known so far, one currently including 35 species from nine families, is presented.

Based on adults collected from leaf litter of a secondary semi-evergreen tropical forest in Mexico, two new oribatid mites (Oribatida) are described: Epilohmannia mexicana sp. n. (Epilohmanniidae) and Plateremaeus bifurcatus sp. n. (Plateremaeidae).

Feathers of an unknown bird of prey were collected on the coastal plain tundra near Meinypil’gyno (62°32′ N, 177°03′ E), SE Chukotka on June 5, 2021. An analysis of the mitochondrial cytochrome b gene and sex chromosome CHD1 gene fragments from DNA isolated from the feathers showed with full confidence that the feathers belonged to a male of the Nearctic Northern Harrier (Circus hudsonius (Linnaeus 1766)), formerly considered as being a subspecies of the Holarctic Hen Harrier (C. cyaneus (Linnaeus 1766)). No specimens of the American Harrier from the northern Far East of Russia are contained in the collections of the Zoological Museum of Moscow State University and the Zoological Institute of the Russian Academy of Sciences. Few other known visual observations of harriers in Chukotka are not properly documented for their correct species identification. The revealed vagrant American Harrier documents the first record of this species in Russia generally and in Chukotka in particular.

In the evolution of proboscideans, the appearance of dwarf and semi-dwarf forms occurred repeatedly, in different territories and at different times, due to a lack of resources caused by geographic isolation on islands and by landscape isolation on the mainland. Despite a significant amount of information on the insular forms of mammoths and elephants, the question of the relationship between a decrease in body size and morphological changes in the dental system remains a matter of debate. Some data show that dwarfism was accompanied by a decreasing number of plates (lophs) and by tooth enamel thickening. Other data show that changes in the dental system on the islands indicate that the number of plates could either decrease or remain unchanged, or even increase. Taking into account the importance of the number of plates as a diagnostic feature in the species identification of proboscidean taxa and the lack of a consensus on the stability of the trend towards a decrease in the number of plates from large continental ancestors to insular dwarf descendants, we (1) summarize the data on the records of small tooth-mammoths of the genus Mammuthus with a reduced number of plates in sites across northern Eurasia, (2) provide new radiocarbon dates, and (3) consider the number of plates as a possible sign of dwarfization in continental mammoths. The small teeth of the last generation of M. primigenius from the coastal part of northeastern Siberia and a comparison with data from other regions show that the posterior sections of mammoth cheek teeth are the most variable and represent a reduction complex. For the woolly mammoth, reduction primarily affects that part of the crown which became more complex by the gradually increasing number of plates during the phyletic evolution in the Middle to Late Pleistocene. The rapid loss of the evolutionary achievements through reduction is not a unique feature of woolly mammoth teeth. This has been observed in other mammals as well. Similar reduction complexes are observed for the cheek teeth of proboscideans and rodents of the subfamily Arvicolinae, as is shown by a decrease in the number of serially homologous crown elements: plates in proboscideans and pairs of prisms in voles. A comparison of the number of plates with the size of the teeth of M. primigenius suggests that a decrease in the number of dental plates, while retaining other specific features of the tooth, can be used as a criterion for separating semi-dwarf and small specimens of the woolly mammoth. The largest decrease in size of mainland mammoths is observed during warming periods, which also showed significant transformations of landscapes in a reduction of available resources.

The distribution of the mass of both down and down feathers along the pterilia of the Demoiselle crane and the Eurasian crane has been described for the first time. Fundamental differences in the plumage structure of these closely related species living in the summer in different climatic zones have been revealed. On the ventral side of the body of the Eurasian crane, the proportion of down and down feathers is significantly greater than on the dorsal side, whereas the proportion of the downy part of the contour feather vane is 1.5 to 2 times less. The additional down feather exceeds 2 cm, as a rule. Such a distribution of fluff ensures effective thermoregulation in this cold- and moisture-resistant species. In the Demoiselle crane, the abundance of down and down feathers on the ventral side of the body is 3 times less than on the dorsal side and 2 times less than in the Eurasian crane. On the dorsal side of the body, the proportion of fluff is almost 1.5 times greater than that of the Eurasian crane. The proportion of the downy part of the contour feather vane on feathers of different sizes on the dorsal and ventral sides is approximately the same. The contour feather contains predominantly umbilical fluff. Such a structure of the integument on the ventral side of the body allows the Demoiselle Crane, an inhabitant of hot climates, to better ventilate the thickness of the plumage and to increase the heat transfer of the body to the environment. The large proportion of downy structures on the dorsal side prevents heat from penetrating the skin.