How sponges ‘spike’ themselves with glass

Sponges are, for lack of a better term, weird. Aside from being some of the most ancient animals on Earth, these marine invertebrates maintain their shape and stiffness with a matrix of glass. Their spiny silica-based spicules grow and branch to form wicked shapes, from thin needles to spiked spheres. But no one knew precisely how sponges could make such a wide variety of symmetrical shapes. So scientists investigated their 3D structure using x-ray nanotomography, a way of peering within tiny structures without destroying them. The internal scans showed that the inside of spicules, also known as axial filaments, are made up of proteins, and these proteins determine the eventual shape of the spicule, the researchers report today in Science Advances. The finding could help engineers and materials scientists produce solar cells and other opto-electronics without the help of the high temperatures required to shape glass today—making this ancient arrangement a boon for modern technology.