Life history strategies of modern and fossil molluscs.

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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)