| Abstract: | The Perkinsiana acrosome is elongated, pointed and tapering, strengthened anteriorly by cortical rings of longitudinally running units. The Pseudopotamilla acrosome is cap-like and its apical region contains a laminar body with two electron densities, the laminae crossed by occasional lines of dislocation, as in a crystal. These apparently solid regions are closely followed by peripherally situated lucent zones. The zone in Pseudopotamilla contains tubules, which are very like those in Sabella sperm, except that they lack connections with the acrosome base. Both species are probably broadcast spawners and have nuclei, mitochondria, centrioles and flagella of the primitive type. This may, however, be a secondary reversion through neoteny. |
