Molluscan Diversity 2(2). December 2010

Original Articles

Discovery of a healthy population of the critically endangered freshwater snail Camptoceras hirasei Walker, 1919 (Gastropoda: Pulmonata: Planorbidae) in Okayama Prefecture, western Japan

Tsukasa ABE and Hiroshi FUKUDA

Abstract A healthy population of the endangered freshwater snail Camptoceras hirasei was found in a paddy field area at the Yoshiigawa River System, Okayama Prefecture, western Honshu. This is the second record and the only living population of the species in the Prefecture. It was confirmed that the species reproduces in the present locality because many minute juveniles and egg masses were found together with adults. The species was found in small channels and ditches with plants on muddy bottom at a depth of 10-40 cm. The water current was flowing at less than 1 cm/s. All of these channels/ditches are temporal waters which are flooded only by rain and/or irrigation. Around the present locality, such habitats in flood plains should be conserved because they are restricted to narrow range and threatened by river improvements, paddy field adjustments, and modifications of ways of agriculture and land use.

Key words: habitat, paddy field area, temporal waters, flood plain, conservation, San'yo District

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Habitat environment of two endangered arboreal land snails, Satsuma (Luchuhadra) amanoi and S. (L.) eucosmia eucosmia (Pulmonata: Camaenidae), in the secondary forests of parkland in Okinawa, Japan

Masatoshi TAKEUCHI and Tomoyuki AONO

Abstract Our objective was to evaluate the habitat preference of two endangered arboreal land snail species by counting the number of empty shells in given areas. Density and spatial distribution of the snail species Satsuma (Luchuhadra) amanoi (Kuroda, 1960) and S. (L.) eucosmia eucosmia (Pilsbry, 1895) were investigated at two sites in parks located at Maezato and Yaese, in the southern area of Okinawa Island. These sites presented a variety of green environments including trees of Ficus (Moraceae), herbaceous plants, mantle climbing plants, and limestone. The empty shell densities of the two snail species were highly variable within habitat quadrats, suggesting a specific distribution pattern. More empty shells were found in quadrates in which fig trees (Ficus virgata Rewin.) and climbing plants were well present, indicating a higher correlation coefficient between the density of empty shells and tree and plant coverage. Conversely, the absence of or a weak relationship between shell density and the degree of coverage by another fig tree, Ficus microcarpa L. f., was also observed.

Key words: climbing plant, empty shell, Moraceae, habitat tree, terrestrial snail, Okinawa Island, Subtropical

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New distribution records of the vulnerable freshwater snail Bithynia inabai Habe, 1985 (Caenogastropoda: Bithyniidae) in northern Hyogo Prefecture and Shimane Prefecture, western Japan

Yuki TATARA, Hiroko TAKEDA and Hiroshi FUKUDA

Abstract Although the natural populations of Bithynia inabai were known only from southern Hyogo Prefecture and central to eastern Okayama Prefecture, we found the species in Toyooka-shi and Yabu-shi, both northern Hyogo Prefecture and Izumo-shi, Shimane Prefecture for the first time. This species was regarded as a possible alien species, but we conclude herein that it is a native species endemic to the narrow range from the western Kinki District to the eastern Chugoku District because it is found mainly in well preserved habitats accompanied with some other endangered animals, e.g. Cipangopaludina laeta, Lethocerus deyrollei and Appasus japonicus.

Key words: Rissooidea, rare species, introduced species, distribution, conservation, rice field, Toyooka-shi, Izumo-shi

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An introduced individual of Satsuma myomphala (Pulmonata: Camaenidae) into Yamagata Prefecture, northern Honshu, Japan

Hiroshi FUKUDA

Abstract live juvenile individual of Satsuma myomphala (Martens, 1865) was found from Yuza-machi, Akumi-gun, northwestern corner of Yamagata Prefecture, northern Honshu. This species has been known to be distributed in southwestern Honshu (the Kanto Region and westwards), Shikoku and Kyushu and never been recorded from the Tohoku Region. Because the present locality was a garden neighbouring human habitation, the individual was probably introduced from western Japan. Although the juvenile shells of S. myomphala and the congener S. omphalodes (Pilsbry, 1901) are quite similar in having widely open umbilicus, it was confirmed that their juveniles are distinguishable from each other in the presence/absence of reddish purple colouration on the inside wall of umbilicus and the present individual is S. myomphala.

Key words: Satsuma omphalodes, land snail, distribution, Red Data Book, Yuza-machi, Akumi-gun, Tohoku Region

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Discovery of males of the alien aquatic snail Potamopyrgus antipodarum (Gray, 1843) (Caenogastropoda: Rissooidea) in Japan, with notes on the new localities

Daichi OGATA, Akane IIDA, Miki NAKAJIMA, Ayuka YAMASAKI, Tetsuji SONOHARA, Yuki TATARA and Takuma HAGA

Abstract The hydrobiid snail Potamopyrgus antipodarum (Gray, 1843) has been introduced into many countries and rapidly spreading in modern Japan. Three new localities of the species were found in Ibaraki and Chiba prefectures. Although the species was known as parthenogenetic only with females in most of introduced populations, we discovered the males from Inage, Chiba-shi, Chiba Prefecture. This is the first record of the male in Japan. In the population, it was experimentally confirmed that females can reproduce without copulation and no evidence of sexual reproduction was provided. We also investigated the habitats of the species in 10 localities from Aomori to Miyazaki prefectures. Their habitats were extremely variable in the salinity of water and the presence/absence of water current.

Key words: Hydrobiidae, introduced species, parthenogenesis, sex reproduction, freshwater, brackish water, habitat

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