The orientation of the mitotic spindle has long been proposed to control cell fate choices and tissue morphogenesis and architecture, and thus play an important role in shaping embryonic forms.It was previously reported that the in ascidian Ciona intestinalis, almost all epithelial cells divide along anterior posterior (A-P) axis during the last division.By live-imaging, we found that a novel membrane structure invaginating into the cells along with A-P polarity.This invagination was formed beneath the apical cortex of the cell and is vertically extended from the membrane.