I mean, if Sojourner had found water on Mars, there probably would have been sponges in it. On this planet, sponges rank one notch above single-celled animals, such as amoebas, on the evolutionary scale. A sponge has no nervous system and no muscles. This means no stomach, no eyes, no pain, no movement. In spite of this, sponges manage to do some remarkable things, beginning with building unusual skeletons.
Some sponges keep their shape by forming spicules, tiny rods that brace up the sponge's cells.
Spicules are made either of calcium carbonate, like the skeletons of stony corals, or of silica, a glasslike material that can stick into, and hurt, human skin. Other kinds of sponges stand up with the support of tough, rubbery fibers called spongin. Sponges containing this soft type of skeleton are the bath and cleaning sponges familiar to us all. Most of them line up to form a network of canals covered with tiny, beating hairs. These hairs move water into the sponge through pores at the surface, and out through holes.