The glass sponges get their name from their skeleton that is made of small rods or long, bristle-like fibers (spicules) made of silica, or glass. The sponge makes the glass with silicic acid it extracts from the seawater. Each spicule is a little spiny cluster consisting of four or six rods at right angles to each other, like a shape you could build with Tinker Toys. The fused spicules create a lattice structure that forms the vase-like shape of a glass sponge. The regular arrangement of the symmetrical spicules makes a glass sponge more symmetrical than most other sponges. The clusters can be highly ornamented with additional branching, creating beautiful skeletal lattices. The arrangement is also functional; it turns out a glass sponge skeleton is 100 times as stiff as an aluminum tube of the same size.

Sponges do not move around much; they are considered to be sessile or fixed in one place. However, research has shown that some sponges can move slowly by shifting their cells in a coordinated fashion. They can reshape themselves to crawl along the seafloor or other surface. They extend parts of their bodies and contract others to achieve locomotion. However, if you attempt to watch a sponge moving, you will likely be disappointed. At best, they move tiny distances, like a couple of millimeters per day. Juvenile sponges are much more mobile. A sponge larva is a little ball of cells with hair-like extensions (cilia or flagella) that allow it to paddle around for a few days until it finds a place to settle down. Once settled, its cells transform to be more appropriate for a sessile organism.