OBSERVATIONS ON “VAMPYRELLA PENULA-STYLODINIUM SPHAERA” AND THE ULTRASTRUCTURE OF THE REPRODUCTIVE CYST

“Vampyrella-Stylodinium,” an artificial name for a predaceous organism of uncertain taxonomic position, has at least three distinct phases in its life history: the amoeboid phase, both free-floating and attached; the feeding cyst or immobile phase; and flagellated gymnodinoid swarmers. The orange free-floating amoeba has unbranched, filose pseudopodia and several contractile vacuoles. When feeding on the filamentous green alga Oedogonium, the pseudopodia shorten and rearrange. After dissolution of part of the Oedogonium cell wall, the amoeba ingests the host protoplast. Then a stalked reproductive cyst may form. This cyst changes color from green to light orange as it matures. At the time of excystment, the cyst has a smooth outer wall, a spinose inner wall, and a well-delineated phagocytic vacuole. As this vacuole moves from its central position to the cyst's periphery, the walls rupture and 2-4 amoebulae emerge. With TEM observations, the reproductive cyst is shown to be multinucleate. Each nucleus is eukaryotic in organization and possesses one nucleolus. Mitochondria have tubular cristae and no structures unique to the division Pyrrhophyta are observed. Although this stage of the life history does not have a dinokaryotic nucleus, the gymnodinoid swarmers that can emerge from the reproductive cyst, do. Like other parasites which have been assigned to the division Pyrrhophyta, “Vampyrella-Stylodinium” does not conform well to the generalized concept of a dinoflagellate.