The stromatoporoid sponge shown in the image, Labechia, would have been a very important part of the Wenlock reef structure.

Detail of living sponge. In this picture you can see the porous texture and fine mesh of spicules.

Sponges are the simplest type of multicellular animal, with little internal structure or organs. Their skeletons consist of springy protein or hard calcium carbonate or silica. The hard skeletons fossilise well.

One group of sponges, the stromatoporoids, have very thick calcium carbonate skeletons, which makes them particularly good at forming reefs.

Sponges are filter feeders. They draw water through their bodies and filter out the tasty bits. They would have been important to the reef ecosystem because they help to keep the water clean by removing particles and bacteria.

Stromatoporoid sponges were very important reef builders on the Wenlock Reef. Their thick calcium carbonate skeletons formed much of the framework of the reef.

The earliest known sponge fossils are from the Cambrian, and are common in many marine environments today.