Fertilization and normal development in Ascidiella aspersa (Tunicata) studied with Nomarski-optics

Abstract

Normal development of Ascidiella aspersa was studied over a period of approx. 24 h at 20°C from egg insemination through metamorphosis of the tadpole larva using Nomarski-optics. Records were made of spermatozoa attaching to and passing through the cellular envelopes and the chorion of the egg. Egg shape alterations upon entry of the fertilizing sperm, which reflect the early phase of ooplasmic segregation, were monitored in intact and dechorionated eggs. The time course of normal development was recorded, and prominent stages were photographed within or deprived of the egg envelopes. The present observations are compared with recent accounts on early development in other solitary ascidian species. © 1989 Biologische Anstalt Helgoland.