Fertilization of marine invertebrates has been extensively studied in classical research. This is not only because a large quantity of gametes can be obtained but also because in vitro fertilization experiments are easier in marine invertebrates than in mammals. Studying marine invertebrates led to the discovery of fundamental biological processes, including the fertilization process. The marine invertebrate Ciona intestinalis type A (another name: Ciona robusta ) is one of the model animals used to study many fields of biology. The availability of draft genome sequences, transcriptomic and proteomics data and gene knockdown and geneediting techniques has supported the progress of C. intestinalis (type A) studies. We are taking this advantage for reproductive biology.