We documented the penetration of sperm into the oocyte and the changes in nuclear behavior in using paraffin sections and fluorescent microscopy. The mature oocyte was egg-shaped, had an unbroken germinal vesicle, and remained in the prophase of the first maturation division. Sperm rapidly attached to the surface of the oocyte within 5 min of insemination, water temperature (21±1) °C. The sperm penetrated into the oocyte at a location close to vegetal pole triggering development of the fertilization membrane. The sperm nuclei then expanded and the fertilization membrane was completed within 25 min. The first and second maturation divisions were completed 10 and 50 min after insemination, and were accompanied by the exclusion of the first and the second polar bodies, respectively. The nuclei of the sperm and egg expanded 50–70 min later, respectively, and developed into the pronuclei. These then migrated to the center of the egg, forming an associated nucleus. The first cleavage was completed after 70–90 min, resulting in two daughter cells. The fertilization process lasted ~70 min, which is slightly longer than in most marine invertebrates. Our observations provide basic information for artificial breeding and the cultivation of new varieties of .