Fertilization and polyspermy in Beroe ovata

Many sperm from other animals penetrate the chorion surrounding the large (1mm) glass clear egg of Beroe to fuse with the egg surface. Sperm of the same animal can only fertilize the egg
in about 30% of the animals. Self fertilization is always possible if the chorion is removed
We have been able to record single or multiple sperm entry the of Beroe (see film). Each sperm entry triggers a localized contraction of the egg surface (see film). In the case of physiological polyspermy, each sperm entry sites can be spotted as a 50 micron sized disc under the surface because each aster produced from introduced sperm centrosome accumulate fluorescent vesicles and mitochondria in their center. Sperm can enter anywhere on the surface. More than 20 sperm can enter the egg and the female pronucleus generated under the polar body at the animal pole migrates under the surface and fuses with one of the sperm nucleus

-Carré D. & Sardet C. (1984) Fertilization and early development in Beroe ovata. Dev. Biol. 105, 188-195.
-Carré D, Rouvière C. & Sardet C. (1991). In vitro fertilization in Ctenophores : sperm entry, mitosis and the establishment of bilateral symmetry in Beroe Ovata. Dev. Biol. 147, 381-391.