| Abstract: | I examined the heterotrophic non-armored dinoflaget-late Actiniscus pentasterias (Ehrenberg) Ehrenberg by light and electron microscopy. Actiniscus pentasterias contains an internal skeleton consisting of two star-like siliceous elements. Special emphasis is given to the flagellar apparatus, the nucleus, and a new type of extrusome, named a docidosome. A three dimensional model of the flagerllar apparatus includes a fibrous nuclear connnective, a posterior striated root, and a dorsal striated component of the longitudinal microtabular root. The nucleus is surrounded by a conspicuous fibrous lamina, also visible in the light microscope. The nuclear pores are situated in annulated invaginations of the nuclear envelope, increasing the nuclear surface area by 15–25%. The docidosomes are rod-shaped membrane-bound structures that terminate in a distinct proximal head. They show very complex substructure, consisting of an inner medulla with highly ordered paired ribbons and an outer cortex. |
