Dictyoceratid sponges do not have the usual mineral spicules (rod-like structures that make up many sponge skeletons). Instead they are made entirely of elastic spongin (protein) fibers organized into networks. This makes their bodies tough and flexible. They are easy to squish, but hard to tear. The surface of their body is typically raised up in little cone-shaped points, making it look like they have goosebumps. The bumps are actually projections from the underlying skeletal fibers, and in some species the bumps are expanded into an armor-like covering. Dictyoceratids have the habit of incorporating debris (such as sand grains or spicules shed by other sponges) into their skeletons, making them harder.

Most bath sponges these days are artificial, but a reminder of when a sponge meant the dried up skeleton of a sea sponge. As long as 4,000 years ago, Greeks were free-diving for sponges in the Mediterranean Sea to sell for bathing. A sponge diver had a dangerous job, facing steep coastlines, sharks, and deep water. Special equipment gradually came into use, starting with a simple rake and advancing during the 1800s to a dive suit with a long tube connected to a boat air supply. The uses of sponges expanded to include cushion stuffing, agricultural fertilizer, scouring pads, and food additives. Modern sponge divers are often sponge researchers (spongologists) with scuba tanks, dive computers, or even submersibles. Research on sponges has allowed us to better understand their value to us. Because sponge cells can tell apart self from non-self, they have served as simple models for study of our immune system. Today, they are mostly used for their pharmacological properties; many sponges contain medicinal compounds.

Sponges live in every ocean on Earth, and in some freshwater as well. They have colonized incredibly diverse habitats, from the deep, cold ocean bottom to warm, tropical seas and rough, rocky shorelines battered by waves. Some sponges are tiny dots, and others large enough for a person to get inside. They also come in a shocking variety of shapes, some quite symmetrical like cups or balls, but many asymmetrical like globs, bushes, or bread crusts. Some excavate limestone, such as mollusk shells, and live inside. Sponges may live alone or fuse with other sponges into large, underwater reefs. It turns out that this variety helps explain their ability to be successful on Earth in so many habitats. Sponges are transformers; they can change their shape by moving their cells around. Their cells can even convert to other cell types to adapt their bodies to whatever habitat or conditions they find themselves.