Local surface modulation correlated with ooplasmic segregation in eggs ofSabellaria alveolata (annelida, polychaeta)

In the eggs ofSabellaria alveolata specific morphogenetic determinants are segregated into the vegetal part of the egg which is constricted off to form a polar lobe during the first cleavages. Segregation is supposed to take place during meiosis. In this paper we describe the appearance of a patch of small blebs at the vegetal pole of the eggs after both the first and the second meiotic division and after the first cleavage, as assessed by scanning electron microscopy. We investigated the possible functional relationship between the segregation process and the modulation of the surface architecture at the vegetal pole by treating the eggs with cytochalasin B during meiosis. As a result, both the appearance of the blebs and the development of lobe-dependent structures in the larva are suppressed. From this result it is argued that cortical processes at the vegetal pole are likely to be involved in the segregation of morphogenetic determinants.