How brachiopods get covered with nanometric silicon chips

The investigation of an early pelagic juvenile of the discinid brachiopod Discinisca cf. tenuis elucidates the so far enigmatic origin of nanometric silicon chips covering the brachiopod's juvenile shell. The siliceous tablets are products of an intracellular process within specialized cells of the animal's inner mantle epithelium. These specialized cells are arranged in a circumferential row and contain vesicles, which provide 'reaction chambers' osmotically separated from the cytoplasm. Up to 15 tablets per vesicle are released into the cell by vesicle burst, followed by a coordinated extrusion onto the periostracum. In conjunction with the conveyor belt mechanism of periostracum formation, the regime of tablet release accounts for the highly ordered arrangement of siliceous tablets in parts of the shell's surface. The siliceous tablets are discussed as a protective cover against solar radiation, inherited from Palaeozoic linguliform brachiopods.