Life history strategies of modern and fossil molluscs.

本项目考虑了现代和化石软体动物的生活史策略，特别参考了双壳纲和头足纲的早期发育、绝对壳生长和功能形态学。本研究结果总结如下：(1)根据日本西南太平洋地区上新世-更新世沉积物中保存完好的幼壳的原螺形态和形态测定，估计了Limopsis、Glycymeris和Venericardia （Bivalvia）几种幼壳的发育类型和幼壳死亡率。(2)根据标记个体和恢复个体的内部壳切片所识别的年增量，分析了日本海岸最近的双壳类的绝对壳生长模式和老化。(3)通过对白垩纪菊石幼体和现代头足类（鹦鹉螺、Sepia和Spirula）幼体壳的显微结构观察对比，提出了中生代菊石（头足目）幼体壳的内蜗胚胎模型。(4)分别通过扫描电镜和水动力实验研究了现代和古双壳果胶类（Bivalvia）内肋的功能意义和壳的水动力特性。(5)研究了西太平洋海百合（criinoid Isocrinus）茎部的生物地理分布和生长速率，为了解深海环境中的生物区系提供了依据。(0霁)

Aspects on life history strategies in modern and fossil molluscs were considered in this project, with special reference to the early development, absolute shell growth and functional morpholog in the Bivalvia and the Cephalopoda. The results of this study are summarized as below.(1) Developmental types and juvenile mortality rates were estimated for several species of Limopsis, Glycymeris and Venericardia (Bivalvia), on the basis of prodissoconch morphology and morpnometry of well-preserved juvenile shells from the Plio-pleistocene deposits in the Pacific regions of southwest Japan. (by Tanabe)(2) Absolute shell growth patterns and aging in selected Recent bivalves from the Japanese coast were analyzed, relying on the annual increments recognized in the internal shell sections of marked and recovered individuals. (by Tanabe)(3) Endocochliate embryo model was proposed for the Mesozoic Ammonitida (Cephalopoda) on the basis of comparative microstructural observations of juvenile shells of the Cretaceous ammonites and modern cephalopods (Nautilus, Sepia and Spirula). (by Tanabe)(4) Functional meanings of the internal ribs and hydrodynamic properties for the shells of some modern and fossil pectinids (Bivalvia) were considered by means of scanning electron microscopy and hydrodynamic experiments respectively. (by Hayami)(5) Biogeographic distribution and growth rate of stalk of the crinoid Isocrinus from the western Pacific were examined, as a basis for understanding the biota in the deep-sea environments. (by 0ji)