Glass sponges in the class Hexactinellida are animals commonly found in the deep ocean. Their tissues contain glass-like structural particles, called spicules, that are made of silica (hence their name). Some species of glass sponges produce extremely large spicules that fuse together in beautiful patterns to form a “glass house”—a complex skeleton that often remains intact even after the sponge itself dies. The skeleton of the glass sponge, together with various chemicals, provides defense against many predators. Nonetheless, some starfish are known to feed on these rare creatures of the deep.

Most glass sponges live attached to hard surfaces and consume small bacteria and plankton that they filter from the surrounding water. Their intricate skeletons provide many other animals with a home.

The most famous glass sponge is a species of Euplectella, known as the “Venus flower basket,” which builds its skeleton in a way that entraps a certain species of crustacean inside for life. This sponge often houses two small, shrimp-like Stenopodidea, a male and a female, who live out their lives inside the sponge. The crustaceans breed, and when their offspring are tiny, they escape to find a new Venus flower basket of their own. The pair inside the basket clean it and, in return, the basket provides food for the crustaceans through its waste. The animals eventually grow too large to escape the sponge, so they are forced to "stay put" for the rest of their lives.