Poecilosclerid sponges are the most diverse group of sponges, with thousands of species ranging from deep ocean to shallow shoreline habitats. Most poecilosclerids share a skeletal feature found in no other sponges. Many of their spicules (tiny, mineralized rods that make up their skeleton) have shovel or hook-like structures on the ends. These anchors (chelae) are scattered throughout their spongy body tissue, making it more rigid. The function of the shovel end is still unknown in most poecilosclerids. However, some poeciliosclerids are carnivorous (rare for a sponge), and their chelae stick out all over their body like a layer of Velcro. Small prey, such as tiny crustacenas, get snagged on the hooked ends. Sponge scientists (spongologists) wonder whether all poeciliosclerids had a carnivorous ancestor with chelae.

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.