Visualization of cement exocytosis in the cypris cement gland of the barnacle Megabalanus rosa

Cementation to substrata during permanent attachment concludes the planktonic larval phase in many sessile marine invertebrates, including barnacles. However, the neural control and the mechanism of cement secretion from cement organs are poorly understood. In the present study, using isolated cement glands from cyprids of Megabalanus rosa, we have visualized cement secretion and demonstrated the stimulatory effect of dopamine and noradrenaline on such secretion. The abrupt disappearance of secretory granules and subsequent omega-figure formation indicated that exocytosis was the major mode of cement secretion. Exocytosis was localized at the apical surface of cement-secreting cells and lasted for over 30 min. Dopamine and noradrenaline also activated the directional transport of secretory granules to the sites of exocytosis. Glyoxylic acid staining provided histochemical evidence for catecholaminergic innervation to the cement glands. These results suggest that gradual, localized exocytotic secretion of cement triggered by catecholaminergic neurones is a key mechanism during permanent attachment by barnacle cyprids.