External fertilization is a strategy of fertilization in which a sperm cell unites with an egg cell in the open, rather than inside specialized organs within the bodies of the parents. Since the morphology of sperm in most species is adapted to mobility in suitably watery liquids, the sperms of aquatic animals take advantage of the water in which they live, and reach the egg by swimming. Typically such sperms have one or more flagella. In many aquatic animals such as coral and hydra, eggs and sperms are simultaneously shed into the water, and the sperms swim through the water to fertilize the egg in a process known as broadcast fertilization.