Reproductive biology, oogenesis and early development in the brood-caring sea anemone Actinostola spetsbergensis (Anthozoa: Actiniaria)

Abstract

1. Actinostola spetsbergensisCarlgren from different Atlantic and Pacific localities has been found to reproduce sexually during the arctic summer. 2. Oogenesis of the remarkably few eggs proceeds inside the conspicuous and histologically altered layers of mesogloea and endoderm. 3. The fertilized egg and all subsequent developmental stages up to the 24 septa stage are surrounded by a peculiar non-cellular envelope by means of which they adhere in the upper part of their mother's interior. 4. Cleavage is superficial and endoderm seems to be formed by combined processes of invagination and multipolar immigration. 5. The elaborate brood-care is assumed to be of special importance for achieving successful development in A. spetsbergensis. 6. By contrast to other brooding anemones there are special brood caring mechanisms, including particular precautions for the developing egg. 7. The reproductive and brooding particularities of A. spetsbergensis have adaptative significance in respect to the ecological conditions of the arctic region. © 1976 Biologischen Anstalt Helgoland.