A sponge is a type of aquatic animal that lives in fresh or salt water. There are many different types of sponges, and they come in a variety of shapes, sizes, and colors. Sponges are simple creatures with no eyes, mouth, or heart. They are mostly composed of water and have very few organs. Although they look soft, sponges are actually very strong and can withstand a great deal of force.
Sponges are filter feeders; they pump water through their bodies tofilter out food particles. Some sponges eat plankton, while othersfeed on bacteria and detritus (decaying organic matter). Spongebodies consist of two layers: an outer layer of cells called theepidermis, and an inner layer of cells called the gastrodermis.Beneath these layers is a network of pores and channels that allowwater to flow into the sponge’s body cavity. This cavity is linedwith flagellated cells called choanocytes (collar cells), whichcreate a current that draws water through the pores and channelsand over the choanocytes’ feeding apparatus. The choanocytescapture food particles from the passing water and pass them toother cell types in the body for digestion.
Sponges reproduce both sexually and asexually. In sexualreproduction, eggs and sperm are released into the water wherefertilization occurs. The resulting embryos develop into newsponges either by settling on a substrate (bottom-dwelling species)or by floating in the plankton (free-floating species). Asexualreproduction occurs when fragments of an adult sponge break offand grow into new individuals; this process is known as fragmentation. Sponges can also produce clones of themselves throughembryo budding; in this process small pieces break off from themain body which then develop into new individuals that aregenetically identical to their parent sponge.