Polymorphism in the rotifer Asplanchna sieboldi. Fine structure of saccate, cruciform and campanulate females.

The morphology of saccate, cruciform, and campanulate females of Asplanchna sieboldi was analyzed by light and electron microscopy. No major qualitative variations were observed in the ultrastructure of the hypodermis, gastric gland and yolk gland of females from the different morphotypes. Campanulate females did, however, possess larger secretory granules in their gastric gland as well as larger and more numerous nuclei in their gastric and yolk glands than both saccate and cruciform females. The structure of the secretory elements in the gastric gland varied between the two clones investigated.