The symposium of the Society of Zoological Systematics was held on September 7th, 2022 (18:00–20:00) as a session of the related topics in the 93rd Annual Meeting of Zoological Society of Japan (Tokyo). The title was “Natural History of Parasites and Mollusks”. Topics related to the theme on mollusks and parasites, such as snail mites, trematodes, and shellfishes of the families Margaritiferidae and Eulimidae, etc., were presented by five speakers: Tsukasa Waki, Mizuki Sasaki, Yuma Ohari, Wataru Kakino and Tsuyoshi Takano.

The genus Riccardoella Berlese, 1923 (Ereynetidae Oudemans, 1931) consists of eight species, and six of the eight species were reported and described from the lungs of terrestrial mollusks, and the remaining two were from soils. In Japan, three of the eight species have widely been reported from terrestrial mollusks. In this manuscript, we introduce species identification based on morphology, distribution, and hosts of these three Japanese mite species. Sampling methods, preparations of slide specimens and virulence of these mites were also added.

Brachylaimoidea Joyeux and Foley, 1930 includes seven families, and most of them use terrestrial mollusks as intermediate hosts. Among them, trematodes of the genus Brachylaima Dujardin, 1843 (Brachylaimidae Joyeux and Foley, 1930) use terrestrial mollusks as both the first and second intermediate hosts. Nine species of Brachylaima have been reported in Japan, and five of them were recently described with their DNA barcodes based on the nuclear 28S ribosomal RNA and mitochondrial cytochrome c oxidase I gene. High specificity of each species to the first intermediate host suggests the diversity of trematodes of Brachylaima including undiscovered species. Panopistidae Yamaguti, 1958 is also a family of Brachylaimoidea, but its taxonomic position in the superfamily is uncertain, because the DNA barcodes of only one species were deposited. In addition, some genera such as Michajlovia Pojmańska, 1973, Urogonimus Monticelli, 1888, and Urotocus Looss, 1899 are treated as incertae sedis because of the lack of genetic data of related species. Additional sampling from the intermediate host snails and the final host and phylogenetic analyses are needed to solve the problems in the taxonomy of Brachylaimoidea.

Digenean flukes are endoparasites of vertebrates and some fluke species have enormous medical and veterinary importance due to their pathogenicity for humans, livestock, companion animals and wildlife. Most of the digenean flukes need gastropod snails as intermediate hosts in their life cycle. The snail species occurring even across human environments also act as intermediate host of pathogenetic digenean flukes. However, parasitological studies usually focus on only the flukes and epidemiological studies using the snail hosts are unpopular after uncovering life cycles, vector-species and treatment methods of the flukes. For epidemiology of fluke infections, the integrated understanding on the relationship between flukes and their intermediate host snails is necessary. This review introduces the recent studies on the relationship between pathogenetic digenean species and their intermediate host snails, and newly discovered problems in the future

In recent years, the classification system of Unionoida (Margaritiferidae, Unionidae) has undergone major changes from conventional methods by shell morphology, due to breakthroughs in approaches based on molecular phylogenetic analysis. We compared the classification system trends of the Margaritiferidae and Unionidae distributed in Japan, and pointed out that there is a time lag to the classification determinations of the latter. Although the scientific names have been changed, the existence, distribution, and ecological information (ex. host fish for glochidia) of two Japanese margaritiferids have been established, and conservation measures and regulations based on the Red List and laws can be expected. On the other hand, the Unionidae consisted of 3 subfamilies, 11 genera and 15 species has increased to 2 subfamilies, 13 genera and 26 species (excluding alien species) by the new classification system reported in 2020. Therefore, information on the distribution and ecology of many new species must be elucidated. A new classification system will be assumed the further revision, especially for the genus Sinanodonta, and the risk of some local populations extinction increase before clarifying the actual situation of species. We are now proceeding to clarify the early life stage of some Unionoida mussels (ex. parasitic stage, salinity tolerance), but insufficient knowledge of the life cycle of Unionoida has prevented the establishment of complete ex-situ conservation methods. Conversion project of numerous reservoirs are that the most important habitats for Unionidae species pressing forward in Japan. In light of this situation, it is hoped that the new classification system that can serve as a basis for on-site conservation will spread throughout as soon as possible to realize comprehensive conservation.

At least ten families of the molluscan class Gastropoda contain parasitic species. Parasitic gastropods exhibit an extraordinarily large number of species and wide varieties of morphologies and host-exploitation strategies. Here, I introduce our evolutionary studies based on molecular phylogenetic analysis for two lineages of parasitic gastropods: Caledoniella (Caledoniellidae) and Eulimidae. Species of Caledoniella parasitize stomatopods (mantis shrimps) and have close phylogenetic kinship to burrow commensals of marine benthic invertebrates. Interestingly, Sigaretornus sp. from mantis shrimp burrows was found to be sister to Caledoniella, suggesting the following evolutionary scenario from free-living organisms to parasites: (1) colonization into benthic invertebrates’ burrows, (2) specialization to mantis shrimps, and (3) habitat-shift to the host body surface with the acquisition of the parasitic nature. Members of the other group Eulimidae show the widest range of parasitic strategies (i.e., temporary, ecto- and endoparasitism) on their echinoderm hosts. Molecular phylogenies of the family have revealed the polyphyly of endoparasitic taxa and repeated evolutionary changes from slender to globose shells. Recurrent specializations to the parasitic mode of life probably have an important role in the diversification of eulimid gastropods.

A specimen of Sargocentron rubrum (Forsskål, 1775) and two specimens of Scarus ovifrons Temminck and Schlegel, 1846, caught by local fishermen off the coast of Kyoto Prefecture, Japan in December 2021, represent the first and northernmost records in the Sea of Japan, respectively. Both species are likely to have been transported northwards by the Tsushima Warm Current. Because the two specimens of S. ovifrons were collected at almost the same time in adjacent areas, it is possible that they had been part of an aggregation of individuals. Because S. ovifrons contains a palytoxin-like toxin, great care should be taken to avoid its accidental sale at fish markets.

From 2012 to 2021, bird surveys were carried out from Kyushu to Hokkaido, Japan, including a zoo, to find feather mites (Analgoidea Trouessart & Mégnin, 1884 and Pterolichoidea Gaud & Atyeo, 1978) from raptors including owls. In this study, we detected eight feather mite species as following: Glaucalges tytonis Dabert, Ehrnsberger & Dabert, 2008, Hieracolichus nisi (Canestrini, 1878), Kramerella bubonis (Lönnfors, 1937), Kramerella aprotuberantia Dubinin, 1953, Dermonoton longiventer (Mégnin & Trouessart, 1884), Petitota aluconis (Buchholz, 1869), Pseudalloptinus aquilinus (Trouessart, 1884) and Pseudalloptinus milvulinus (Trouessart, 1884).Two of the mite species, G. tytonis and Ps. aquilinus, were only sampled from bird hosts born in the zoo of Japan but they probably originated from oversea. The five of the eight species, Hi. nisi, K. bubonis, K. aprotuberantia, D. longiventer and Pe. aluconis were first reported in Japan. Among them, Hi. nisi was detected only from endangered bird host species Aquila chrysaetos (Linnaeus, 1758)(EN: Endangered). For the mite species, it is important to examine the status of their populations to consider the extinction risk in Japan, because they may be threatened with extinction simultaneously with the decline of the host populations in the future. Three species of mites, G. tytonis, D. longiventer, Hi. nisi were first reported from the hosts Bubo bubo (Linnaeus, 1758), Strix uralensis Pallas, 1771, Haliaeetus albicilla (Linnaeus, 1758), respectively. The Ps. milvulinus was also the first reported from the hosts Buteo japonicus Temminck & Schlegel, 1844 and A. chrysaetos.

The dicrocoeliid trematode Lutztrema attenuatum (Dujardin, 1845) has been reported from its definitive hosts, passerine birds worldwide, whereas its larvae have never been detected in natural fields. In this study, 41 adults of Lu. attenuatum were obtained from dead specimens of Turdus pallidus Gmelin, 1789 and T. eunomus Temminck, 1831, and the partial sequence of the mitochondrial COI gene and nuclear 28S rDNA were determined from one of the specimens as DNA barcodes. Furthermore, during a land snail survey in Tokyo, Japan on 11 August 2021, dicrocoeliid sporocysts and cercariae were detected from the achatinid Allopeas satsumense (Pilsbry, 1906). The partial COI sequence of the sporocysts showed a p-distance value of less than 1.4% to that of the adult Lu. attenuatum. The sporocyst was identified molecularly as Lu. attenuatum based on an empirical intraspecific genetic variation in dicrocoeliids, and thus A. satsumense found to be its first intermediate host. We also provided DNA barcodes to an adult specimen of Lyperosomum sp. (Dicrocoeliidae) detected from the same dead specimen of T. pallidus.