Behavior of endodermal "button cells" during metamorphosis of ascidian larvae

Swimming larvae of Phallusia mamillata are known to have "button cells" of endodermal origin between the ventral surface of the pharynx and the epidermis, that are stainable by various techniques. By immunofluorescence with anti-tubulin antibody and confocal laser microscopy, we obtained a bright reaction at one pole of the cells, suggesting the presence of a cap of tubulin and of microtubules overlaying the nucleus. During metamorphosis the microtubule-rich pseudopods at their base reach the epidermis, especially in the area near the adhesive papillae. Then they emigrate through the epidermis and become roundish again.