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.

Glass sponges live on the bottom of the ocean, as deep as 2,000 meters (about 6,500 feet) or more. They have special structures to anchor them and keep themselves upright. Those that live on sand, for example, have long tufts of fibers sticking out of their bases. Glass sponges are adapted to really cold water and are most abundant in polar regions such as Antarctica. The only time they are found close to the sea surface is when surface waters are chilly, such as below ice or where deep waters are upwelling to the surface. They were found in a Mediterranean cave, for example, only meters from the surface, thanks to a trapped mass of cold water. Glass sponges tend to live in clusters and have formed a reef in British Columbia that towers nearly 20 feet above the seafloor.

Sponges do not have nervous systems, but a glass sponge has a unique set-up that allows it to conduct electrical impulses around its body in response to stimuli from outside. As its body cells divide, they do not separate completely. They remain connected by bridges of cell material, resulting in a mega-cell that looks like a spider web. This web of soft tissue (called a syncytial network) is wrapped around a mineral skeleton for support. When the mega-cell gets stimulated by something outside, an impulse travels rapidly from one part of the sponge to another, across the cell-cell bridges. This function is similar to what our nervous system does, and may allow a glass sponge to respond to signals from its environment.