In sexual reproduction, there must be some way of getting the sperm to the egg. Since sperm are designed to be mobile in a watery environment, aquatic animals can make use of the water in which they live. In many aquatic animals such as coral or hydra, eggs and sperm are simultaneously shed into the water, and the sperm swim through the water to fertilize the egg in a process known as broadcast fertilization. In many fish species, including salmon, the female will deposit unfertilized eggs in the substrate and the male will swim by and fertilize them.
Many land plants make use of external fertilization as well.
Structure and Formation of the Unusual Sperm of Patelloida Latistrigata (Mollusca: Patellogastropoda): Implications for Fertilization Biology
Apr 01, 2012; Introduction After extensive studies of invertebrate sperm structure. Franzen (1955. 1956) concluded that despite considerable...