[in Japanese]

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[in Japanese]

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The growth rate of the Nautilus shell is still uncertain because their main habitat is "deep sea". In 1977-1978 (during 57-328 days) the shell growth in the seven specimens of Nautilus macromphalus SOWERBY was measured in the Yomiuri Land Marine Aquarium, Tokyo. The total shell growth of the specimens ranged from 0 to 30 mm (Table 1). By the relationship between shell growth and maximum shell diameter (Figs. 8A, 3), specimen No. 15 (shell diameter 125 mm) is regarded as juvenile, Nos. 10-13 (139-152 mm) mature, and Nos. 8 and 14 (163-164 mm) gerontic shells. The juvenile specimen showed a little growth (6.0 mm), and the mature specimens with the exception of No. 10 showed substantial growth (13.2-29.5 mm). The gerontics, however, showed little or no growth. The fluctuation of water temperature in the acrylic resin rearing tank is given in Figure 2B. The quality of water became worse with time (e.g. accumulation of NO_3-N) because of the closed circulating water system. The average daily food intake per total body weight decreased with time (Fig. 2B), and the average daily growth rate of the specimen No. 12 also declined with time (Fig. 2A). Therefore, the growth rate of the Nautilus shell can be thought to decline in old rearing water due to decline of its food intake or other conditions involved.

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The chromosomes of Crassostrea rhizophorae (GUILDING, 1828) from Estero del Pargo, Isla del Carmen, Campeche, Mexico, were analysed by using routine cytogenetic techniques of gonadal tissue to obtain mitotic and meiotic chromosomes. The diploid number (2n) was 20. All chromosomes were biarmed and the arm number was 40. From the cytogenetic point of view, the karyotype of this species was only metacentric and submetacentric chromosomes as in the case of other Crassostrea species already studied.

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As the original description of the genus Mundiphaedusa was only in a concise style, here presents detailed diagnosis as follows : Genus Mundiphaedusa KURODA & HABE in HABE, 1958 Type species : Clausilia ducalis KOBELT, 1876 Diagnosis : Shell club-shaped, medium to large for the Clausiliidae. Surface polished, lustrous, yellowish brown in color. Protoconch with blunt apex. Subcolumellar lamella emerges, but rarely immersed. Palatal plicae 1-5 in number and sometimes lunella presents. Clausilium has no slit on the inner side. In the present paper, five species of the genus Mundiphaedusa are discussed in viewpoint of morphology of the genitalia and distribution.

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