The structural features of normal and abnormal embryo attachment systems of the Chinese mitten crab Eriocheir sinensis
were investigated by scanning electron microscopy. The results showed that the volume of incubation fluid in the brooding chamber increased 15 minutes after egg-laying, immersing the embryos in the incubation fluid and thus the egg envelop became very sticky immediately. The egg stalk was largely formed within 30 minutes and completed within 80 to 140 minutes after egg-laying, so that the egg envelop became strongly adherent to the ovigerous hairs. In normal embryos, the egg stalks were highly twisted and the embryos were attached to the ovigerous hair by the egg stalk or funiculus. Many villiform were found on egg stalks and a lot of mucus was also found on the ovigerous seta. In abnormal egg stalks, villiform were never found, though numerous epibionts were attached to the embryo surface and egg stalk. The mucus of ovigerous hair and the villiform of egg stalks may contribute to egg attachment. Because of the epibionts the structure of egg investment coat egg stalk and funiculus were changed, enhancing the attrition between embryos and making embryo respiration difficult. The death and loss of embryos occur because of the above reasons.