Sponges are animals that do incredible impressions of inanimate objects. They have no nervous, digestive, or circulatory systems. They have no symmetry—no left or right, no front or back. And their bodies comprise just two layers of cells, sandwiching a jelly-like filling.

With such simple body plans, you might expect sponges to be flaccid and soft. In fact, they can be sturdy and tough, because their jelly-like middle is often full of microscopic pieces of hard minerals, known as spicules. They come in a beautiful range of shapes: spines, grappling hooks, jacks, pollen-like spheres, and coralline branches. The spicules act like an internal skeleton, giving the sponges shape and support.

Now, Noriko Funayama’s group at Kyoto University has discovered how sponges build this skeleton,