A new vesicomyid clam Calyptogena similaris n. sp. is described at the depth of 2084 m of the Nankai Trough, off Pacific coast of Honshu. This taxon is externally resembles C. nautilei Okutani & Metivier, 1986 from depths around 3, 800 m in the Tenryu Submarine Canyon in general appearance and size, but this species has more elongate shell with a broad posterior portion with wing-like appearance. The analysis of nuculeotide sequence of mitochondrial DNA endorsed that this is different from any other known Calyptogena species from Japanese waters.

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Shell morphology of Calyptogena soyoae-complex (Bivalvia : Vesicomyidae) was compared between the two mitochondrial haplotypes that had been revealed by the previous genetic study. Significant morphological differences between the two haplotypes were detected by an analysis of covariance of shell length-height relationship and by t-test of the average value of length-height ratio. On the basis of the molecular and morphological differences between two haplotypes, Calyptogena okutanii n. sp., a sibling species of Calyptogena soyoae, is established from the seep area off Hatsushima Island, Sagami Bay, central Honshu, Japan.

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Diplommatina (Sinica) hidaensis n. sp. from Gifu and Nagano Prefectures is described. This new species is characterized by whorls with clear and fine axial rib, absence of the 2nd labia, very short palatal plica and small nuclear DNA value. Chromosome number and karyotype are 2n=26 and 18M+4SM-M+4SM, respectively.

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北海道中央部に分布する前期白亜紀の後期アルビアンの前期(106 Ma), と三浦半島の中央部に分布する中期中新世初期(15 Ma)の地層から産出した, ともに良く似るスエモノガイ科の二枚貝化石を検討した。三浦半島の葉山層の粘土岩から採集された化石は, Shikama(1968)によってThracidora giganteaと命名された。しかし, 本種は殻が非常に大きく(殻長約140 mm), 厚く, 殻頂が中央にあり, その外形は楕円形で, 殻の後端に切断面がない, という特徴はワタゾコスエモノガイ属Thracidoraと大きく異なることから, 本属は同属に含まれない, との結論に達した。一方, 北海道三笠市の幾春別川支流の奔別(ぽんべつ)川の中部蝦夷層群下部のシルト岩から採集されたスエモノガイ科化石は円形に近い楕円形で, 三浦半島産の化石よりさらに大型(約180 mm)で, 厚い殻はよく膨らんでいる。この2種類のスエモノガイ科化石はスエモノガイ科の中で形態が特異であるので, これらをスエモノガイ科の新属としてNipponothracia属(ニッポンスエモノガイ)を提唱する。北海道の白亜紀(106 Ma)の新種N. ponbetsensisと三浦半島の中新世(15 Ma)のN. giganteaは両種とも泥岩中から合弁で産出し, 周辺に炭酸塩のコンクリーションを伴う。Nipponothracia属は, 化学合成細菌を体内に共生させていることが知られているSolemya属, Calyptogena属, Conchocele属と共産しているので, Nipponothracia属もこれらの属と同様の生態をもつ化学合成動物と考えられる。

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フタオビザルガイChama pulchellaは一般には左殻で固着する小型のキクザルガイ科二枚貝である。浮遊幼生期終わりごろの殻の大きさは, 殻長0.7∿1.1 mm程度で, 原殻に近い部分には針で突いたような微細な孔が多数あり, 周縁側の部分には放射状細肋がある。オーストラリア, 珊瑚海, フィリピン産の標本を観察した結果, クィーンズランド南部フレーザー島で採集されたフタオビザルガイ16個体中15個体は左殻固着で正常な〓歯を備えていたが, 1個体は右殻固着で正常な〓歯を持っていた。これまで, キクザルガイ科二枚貝の〓歯の研究では〓歯の逆転と固着殻の逆転は常に伴っていると考えられてきたが, 〓歯の逆転と固着殻の逆転は独立に起りうることが分かった。

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The enigmatic Japanese species Bertinia bertinia Jousseaume, 1883 is currently placed within the notaspidean opisthobranchs. However, detailed examinations of the shape, colour and microstructure of the type material, have shown that this name is actually based on the spatula shell layer of the patellogastropod Cellana nigrolineata (Reeve, 1854), of which it is therefore a junior synonym.

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ドブシジミの殻体に存在する管状構造の内容物(caeca)の微細構造を透過型電子顕微鏡を用いて観察した。管の内部は外套膜外面上皮を構成する細胞から伸びる突起によって満たされている。突起の先端部は殻皮に達しており, 外表面を微絨毛で覆われ, 軸の内部には多数のミトコンドリアや粗面小砲体, 微小管が存在する。ドブシジミのcaecaの微細構造は, 系統的に遠く離れたフネガイ目二枚貝のcaecaの微細構造に極めて良く似ていることから, caecaはそれぞれの系統内で独立して獲得され, おそらく共通した機能を果たしているものと想像される。

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In the stylommatophoran pulmonates, the little hermaphrodite (ovotestis) duct leads into a complicated system of ducts and pouches in the proximal part of the albumen gland. This region is the carrefour and is given various names, e.g. talon, fertilization chamber complex and caecum. Internal system of the region consists of two basic structures, the fertilization pouch and the spermathecal sac. In the complex system of Acusta despecta sieboldiana, the distal end of the ovotestis duct enters a fertilization pouch with a blind sac called spermathecal sac (receptaculum seminis, seminal receptacle), which communicates with the pouch through an opening pore on the middle area of the pouch. We found that the ova generally came through the ovotestis duct into the fertilization pouch before breakdown of the germinal vesicle and then underwent maturation division. Fertilization may be performed by stored foreign sperm in the spermathecal sac.

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先島諸島3島でのオニヒザラガイ(Acanthopleura gemmata), リュウキュウヒザラガイ(A. loochooana), キクノハナヒザラガイ(A. tenuispinosa), コザネヒザラガイ(A. miles)の分布を調べた。オニヒザラガイとリュウキュウヒザラガイは, 沖縄県瀬底島で調べた例と同様に3島の海岸に波当たりの程度に応じて分布していた。キクノハナヒザラガイとコザネヒザラガイは, 宮古島ではその波当たりの程度に応じて分布していたが八重山諸島の2島では発見されなかった。コザネヒザラガイが見られなかったのは, 同種の生息に適当な強い波当たりの海岸が存在しないことが理由として考えられる。しかし, なぜキクノハナヒザラガイが見られなかったかについては, 地理的な分布範囲からも生息環境の点からも説明できない。その他, 考えられるいくつかの要因を列挙した。

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Generation of the streak-like flash in the inner-fold of the mantle in Ctenoides ales was investigated by video-camera recording, and stereo, light, fluorescence and electron microscopy. The stereo microscopy revealed the presence of a pale white band along the entire width of the marginal edge of the shell side surface of the inner fold. Since the flashing could not be seen in the dark, it was not due to the luminescence but the reflection of light. The light microscopy showed that the band region consisted of about ten rows of epithelial cells, cylindrical and 40 μm tall and 10 μm wide. The cytoplasm was densely filled with fine granules, eosinophilic in H-E staining. Under the electron microscope, those granules appeared as electron-dense vesicles, 0.5-0.6 μm in diameter, each containing a highly electron-dense spherical core, 0.2-0.3 μm in diameter. The cell had a nucleus, few mitochondria and lysosomes, however, other cellular organelles such as Golgi apparatus, rough and smooth endoplasmic reticulum were not evident, in the present observation. We assume that the electron-dense vesicles packed in the cytoplasm function to reflect light strongly. This highly reflecting structure found in C. ales is quite different from those have been reported in eyes of scallop and squid, and in iridophores of giant clam, cuttlefish, long-spined sea urchin and of fishes. The video observation showed that the mantle made a movement to roll the white band towards the shell-side and then, within a second, the rolling movement was released. The phase of the movement was different by the portions of the mantle, and the mantle edge made a wave-like motion. When the pale white band was hidden by the roll, the reflection of light disappeared. When the rolling was released, the reflection of light reappeared. Since the "roll and release movement" repeat quickly, it looks as though a streak-like flash run along the mantle margin.

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