Neoskrjabinolepis paradoxa n. sp. from shrews on Sakhalin Island, Russia, with an amended diagnosis of Neoskrjabinolepis Spassky, 1947 (Cestoda: Cyclophyllidea: Hymenolepididae), a key, and a review on geographical distribution of the species.

A taxonomic review was performed on cestodes of the genus Neoskrjabinolepis Spassky, 1947 that parasitize different species of Sorex shrews in different regions of the northern Palearctic and in the Nearctic (Alaska, USA). Information on Palearctic Neoskrjabinolepis cestodes published in various articles is summarized. An overview of the geographical distribution of the Neoskrjabinolepis species is also presented. Currently, the genus includes 17 species. In the European part of the Palearctic, four species of the genus are registered; in the Asian part, 13 species; and on the American continent (Seward Peninsula, Alaska, USA), two species. Descriptions, illustrations, and differential diagnoses are given for a new species of Neoskrjabinolepis, i.e. N. paradoxa n. sp., which was found in shrews Sorex unguiculatus Dobson and S. caecutiens Laxmann on Sakhalin Island. A unique feature of the new species is irregularly alternating genital pores in the uterus series in the strobila. Amended new differential features (positioning of the uterus relative to osmoregulatory canals and alternation of genital pores) of genus diagnosis and an identification key for Neoskrjabinolepis spp. are presented.

Larval spirurids in a supralittoral amphipod in the north-east of Russia and the identification of the intermediate host of Antechiniella septentrionalis (Spirurida: Acuariidae), parasitic in a tundra vole.

The supralittoral amphipod Traskorchestia ditmari (Derzhavin, 1923) was identified as the intermediate host for Antechiniella septentrionalis Ivanova, Dokuchaev & Spiridonov, 2019, a parasite of the tundra vole Microtus oeconomus and Skrjabinocerca sp. (both Spirurida: Acuariidae) in Magadan Oblast in north-eastern Russia. Joint infection by both larval spirurids was not observed. The infective stage of A. septentrionalis was the encysted larvae, while larvae of Skrjabinocerca sp. were free in the amphipod's coelom. The identity of A. septentrionalis was confirmed using cox1 mtDNA gene analysis, performed on adult stages from a tundra vole and on larvae from amphipods. Possible transmission routes of A. septentrionalis are discussed.

Antechiniella septentrionalis n. sp. (Spirurida: Acuariidae), a new intestinal nematode parasite of the tundra vole Microtus oeconomus (Pallas) (Rodentia: Muridae) in the north-east of Russia.

Antechiniella septentrionalis n. sp. (Spirurida: Acuariidae) is described from the duodenum of a tundra vole, Microtus oeconomus (Pallas), collected in the Magadan region in the north-east part of Russia. It differs from A. suffodiax (Beveridge & Barker, 1975) and A. sertatum Smales, 1991 mainly in having a larger number of postcloacal papillae (5-6 pairs vs 4 pairs), a differently shaped left spicule, the disposition of precloacal papillae in two rows vs one, and oblong vs oval eggs. Other differences include the different disposition of ovaries in A. septentrionalis n. sp and A. suffodiax and the different structure of deirids in A. septentrionalis n. sp. and A. sertatum. The new species was characterized molecularly (partial sequences for 18S rRNA, 28S rRNA and cox1 mtDNA). The phylogenetic analyses performed showed the affinity of the new species to the members of the Acuariidae and other spirurid nematodes.

[A case of the tick (Ixodidae) hiperinvasion of the tundra vole in magadan environs].

A case of tundra vole death as a result its hyperinvasion by ticks Ixodes angustus on the northern periphery of the Asiatic range of the parasite is given.

[Fleas of small mammals from the northeastern Russian Far East].

Results of the study of fleas (Siphonaptera) collected from small mammals (insectivores and rodents) in the Russian Far East (Magadan Province, and Khabarovsk and Kamchatka Territories) are represented. Fourteen flea species were revealed in 17 species of small mammals.

[Genetic diversity of the striped field mouse (Apodemus agrarius Pallas, 1771) in the Russian Far East as assessed by RAPD-PCR].

Random amplified polymorphic DNA (RAPD) analysis based on polymerase chain reaction (PCR) with ten-nucleotide primers of arbitrary sequences (RAPID-PCR) was used to study the genetic characteristics of five samples of the striped field mouse (Apodemus agrarius Pallas, 1771) from the Russian Far East (Primorye, Khabarovsk krai, and Magadan oblast). Highly significant differentiation of the samples was demonstrated, the genetic diversity of each sample was estimated, and non-neutral loci were found. The genetic diversity was the highest in a population from the outskirts of Magadan and the lowest in populations from an island on the Amur River island near Khabarovsk and from the village of Talon (Magadan oblast). These two last populations were found to be genetically close to each other. These results indicate that striped field mice have been repeatedly introduced to Magadan oblast. The Talon population is likely to have originated from the left bank of the Amur; the outskirts of Magadan are inhabited with a mixed population formed by mice from Primorye and other regions.

Intraspecific phylogeny and geographical variation of six species of northeastern Asiatic Sorex shrews based on the mitochondrial cytochrome b sequences.

Intraspecific phylogeny and genetic variation were investigated based on nucleotide sequences of the mitochondrial cytochrome b gene in six soricine shrew species, Sorex unguiculatus, S. caecutiens, S. shinto, S. gracillimus, S. minutissimus and S. hosonoi, collected primarily from northeastern Asia. Maximum likelihood trees and a phylogenetic network were generated to estimate intraspecific phylogenies. S. minutissimus showed high congruence between phylogenetic position and geographical origin and S. gracillimus showed low congruence. In contrast, there was no congruence between phylogeny and geography in S. unguiculatus and the S. caecutiens from Sakhalin-Eurasia. Positive correlation between genetic and geographical distances was found in S. minutissimus and S. gracillimus, but not in the other species (or regional populations). The results of the phylogenetic and genetic analyses suggest that S. minutissimus and S. gracillimus have occupied their present ranges for a longer time than the other species if we assume a stepping-stone model of population structure. In addition, there was no contradiction between the present investigations and the hypotheses of multiple immigration by S. gracillimus and a single immigration by S. unguiculatus into Hokkaido Island. It is proposed that these six northeastern Asian species experienced different historical processes of range expansion and dispersal despite the fact that some of them currently show similar patterns of distribution.