Phylum Porifera, which means a pore bearer, also known as sponges, do not have a muscular system. They are some of the oldest known animal fossils. There are approximately 5,000 living sponge species which are characterized in three specific groups: Hexactinellida, Demospongia, and Calcarea.
Sponges do not have organs and are comprised of a multicellular system that works together. They are also characterized as having a feeding system. They do not have mouths but instead they have tiny pores in their outer walls where water is drained. The cells in sponge walls filter food from the water as the water is pumped through the body and out of larger openings. The flow of water is unidirectional and is driven by the beating flagella, which line the surface of chambers connected by a series of canals. Sponge cells perform a variety of body functions and seem to be more independent of each other than cells of other animals.