Studies on systematic relationship of diatoms based on their sexual reproduction in culture.

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Objectives of this research project are the followings; 1)Inducing the gametogenesis of diatoms under laboratory culture conditions, 2)Analysis of the systematic relationship of diatoms based on their structures of auxospore coverings, 3) and based on their life cycle patterns, in particular to their sexual reproduction processes.We could accumulate the significant results of four taxa; Melosila moniliformis var. octagona, Actinocyclus sp., Thalassiosira lacustris and Eunotia tropica, for analizing the systematic and phylogenetic relationship of diatoms. These are briefly reported, focusing on their sexual reproduction processes.M. moniliformis var. octagona: monoecious, four sperms hologeneusly born from the mother cell(new finding), auxospore formed by a sperm with a flagellum penetrating into an oogonium, scally perizonia covering with the auxospore in which a large initial vegetative cell is produced.Actinocyclus sp.: monoecious, four sperms merogenously formed from the mother cell(30-50um), auxospore formed by the same manner as M. moniliformis var. octagona, and covered with scally perizonia(new finding), bearing an initial of the vegetative cell(90-130um).Thalassiosira lacustris: monoecious, eight sperms merogenously formed from the mother cell, auxospore(ca.30um) formed by the same manner as M. moniliformis var. octagona, and covered with scally perizonia(new finding), bearing an initial vegetative cell(ca.80um).Eunotia tropica: dioecious(first case in the Protoraphidioideae), pairing cells producing a gamete in each, gametes fusing and becoming a auxospore covered with band-shaped perizonia which possess similar pattern of notches to those of scally ones in a part.