When you think about a sponge, you probably think of something used to wash the dishes in your home. But, believe it or not, sponges are also a group of water-dwelling animals with about 5000-8000 known species (4,6)—and perhaps as many as 15,000 to 24,000 including those not yet discovered (2,6) —that actually have a lot in common with the squishy, water-absorbing things sitting next to your kitchen sink! These strange creatures, which live around the world (5) in oceans and smaller bodies of waters at both shallow and deep levels (2), come in all colors and sizes (2,5,6,) from half an inch (1.3 cm) to five feet and ten inches (178 cm) (6). Their bodies can have shapes that resemble cups, tubes, fans, trees, balls, shapeless blobs, and more (2). But whatever their shape, all sponges share an amazing physical feature that no other animals have: the cells that make up sponges’ bodies can move around freely and change forms, allowing sponges to constantly reshape their bodies (1,2). Most sponges also have special bodies adapted to a lifestyle known as filter-feeding (2,6). (The exceptions are a bizarre group of sponges which are carnivorous, feeding on small crustaceans (5,7)). Filter-feeding sponges pump water into their bodies through special holes, draw small food particles such as bacteria out of the water that comes in, and then let the water keep flowing through a network of canals until it leaves the sponge through one or more other holes (1,2,4,5,6). If you think this sounds pretty simple, you’re right. Sponges are so simplistic they may be the most ancient animals on Earth (2,3,6)!
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