New data on nudibranch molluscs of the genus Dendronotus in the North Pacific are presented. For the first time, the presence of the nudibranch Dendronotus primorjensis Martynov, Sanamyam & Korshunova, 2015 in the Japanese fauna is confirmed using molecular data. Recently collected Japanese specimens of D. primorjensis from Hokkaido are compared with those from the type locality of this species in the Sea of Japan, Russia, using external and internal morphological data. Furthermore, the presence of the species Dendronotus robilliardi Korshunova, Sanamyan, Zimina, Fletcher & Martynov, 2016 is also reported from both the Japanese fauna in the NW Pacific and in the NE North American Pacific. Molecular data for D. robilliardi from the NE Pacific (Port Orchard, Washington State, USA) are reported here for the first time, whereas D. robilliardi was identified from Japan via photographic records using the previously inferred robust molecular and morphological framework for this species. Finally, the species Dendronotus kalikal Ekimova, Korshunova, Schepetov, Neretina, Sanamyan & Martynov, 2015 is reported from the Kuril Islands, which is the first record outside of the type locality in Kamchatka.
Forest clear-cutting and the subsequent habitat fragmentation causes catastrophic damage to plant and animal communities as well as the entire forest ecosystem. Many studies have suggested that forest disturbance decreases the biomass and species richness in forests. However, the long-term influence of deforestation on local-scale patterns of diversity is poorly understood. I investigated the land snail fauna in the soil of primary and secondary forests and compared the number of individuals and species richness in each. Two primary forests and two secondary forests were surveyed in Kuromatsunai District (Hokkaido, Japan), and they were all dominated by the Japanese beech tree, Fagus crenata. Six soil blocks (50 cm × 50 cm) were sampled from each forest, and all the land snails from each soil block were collected and identified. The number of individuals and species richness were subsequently compared between the primary and secondary forests. A significantly larger number of individuals and significantly greater species richness were recorded in the primary forests (generalized linear mixed models (GLMMs), likelihood ratio tests, P < 0.05). The diversity of the land snail fauna in one of the two primary forests, Utasai Forest, was particularly high, with an average of 239.2 individuals and 7.2 species per soil block. In contrast, only 12.3 individuals and 4.8 species, on average, were detected in the two secondary forests. In addition, the number of individuals of smaller species (2.0 mm or less) was significantly lower in the secondary forests, but that of the larger species (greater than 2.0 mm) was not. I also estimated the age of the two secondary forests using an increment borer and found that both secondary forests were cleared approximately 100–150 years ago. My results imply that the deforestation of more than 100 years ago continues to impact the land snail fauna, thus affecting the soil fauna of the forest.
Host species for the glochidia of the freshwater unionid mussel Sinanodonta sp. from Lake Biwako were identified by determining whether the glochidia infected 18 fish taxa in autumn. The fishes were kept in tanks for 11–16 days after glochidial infection, and the numbers of glochidia and metamorphosed juveniles detached from the hosts were counted. All adults of the mussel which used for the experiments were identified by Sinanodonta calipygos from the form of shells and season of released glochidia. Living juveniles of S. calipygos detached from Candidia temminckii, Oryzias sp., Acanthogobius flavimanus, Gymnogobius urotaenia, Trichogaster trichopterus, Rhinogobius similis and Rhinogobius sp. Therefore, these fishes were identified as suitable host species for the glochidia of S. calipygos. Some native fishes that inhabit Lake Biwako (e.g., Gymnogobius urotaenia and Rhinogobius sp.) are considered to be useful local hosts.
The karyotypes of three species of the genus Semisulcospira at Lake Biwa and the Uji river, Japan were reexamined. The observed diploid chromosome number was as follows: Semisulcospira reiniana, 2n=36 (28M+6SM+2ST); S. nakasekoae, 2n=22 (18M+2SM+2T); S. morii, 2n=32 (20M+10SM+2T). The number of chromosomes in S. niponica group ranged from 2n=18 to 32, but no case of 2n=30 has been reported. The number of chromosomes in S. libertina group was 2n=36 with a variation of karyotypes.
The glochidia of the freshwater pearl mussel Margaritifera laevis infect the host fish, the Masu Salmon Oncorhynchus masou masou. The salinity tolerance of these glochidia was investigated in a laboratory experiment in 2016. Masu Salmon infected with glochidia in early May were reared in fresh water from early May to 7 June, then in artificial seawater (salinity: 0–35 psu) from 7 to 10 June (for 72 hours), then again in freshwater from 10 to 30 June. Live juveniles detached from the host fish were observed on 30 June. These results suggest that glochidia of the freshwater pearl mussel exhibit temporary salinity tolerance while on the host fish.