The pumping is done by choanocytes, flagellated cells lining internal chambers whose beating flagella drive flow through a branching canal system. Water enters through ostia across the surface, passes the collar cells where particles are captured, and exits through the large central osculum. Nothing about the process involves muscle.
The capture is fine-grained. Sponges of this type retain bacteria and picoplankton that most reef filter feeders cannot handle, and they also take up dissolved organic carbon. Their metabolic waste supports the so-called sponge loop, which returns reef carbon to larger consumers by way of shed sponge cells.
The barrel is often described as the reef's vacuum cleaner, which understates what makes it interesting: it processes material at a size class other animals ignore. The sponge is also called the redwood of the reef, and the largest individuals have been estimated at many centuries in age, but those ages rest on growth-rate extrapolation rather than on direct dating and should be treated cautiously.