My research tested hypotheses about the evolutionary origin of a novel feature by modification of development. The novelty is the growing larval shell of gastropod molluscs, which emerged when gastropod larvae acquired the ability to feed. One hypothesis states that the growing larval shell in the Heterobranchia is a continuation of the embryonic phase of shell secretion. The second hypothesis states that the larval shell in the Caenogastropoda may be a precocious juvenile shell. These hypotheses implicate heterochrony. To test these hypotheses, I examined ultrastructural features of the shell-secreting cells of two or three life history stages in a member of each of four clades of gastropods: the Patellogastropoda, Vetigastropoda, Caenogastropoda, and Heterobranchia. My results are consistent with the first hypothesis, but I found no ultrastructural support for the second hypothesis. These results provide the most comprehensive comparative data set on the ontogeny of shell-secreting cells for the Gastropoda. / Graduate / 0433

京都大学 / 新制・課程博士 / 博士(理学) / 甲第24826号 / 理博第4975号 / 新制||理||1710(附属図書館) / 京都大学大学院理学研究科生物科学専攻 / (主査)准教授 中野, 智之, 教授 朝倉, 彰, 教授 森, 哲 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM