Structure and encystment in some fossil cavate dinoflagellate cysts

Abstract. A study of some peridinioid and gonyaulacoid cavate cysts which develop a dorsal archaeopyle with a double aperture reveals two significant morphological differences. First, the physical separability of the outer and inner body can only be demonstrated in the peridinioid cysts. Second, although the peridinioid double aperture is covered by two opercula, only the inner aperture is operculate in the corresponding gonyaulacoid archaeopyle. These differences reflect two fundamentally different structural and encystment styles. In the peridinioid cysts, the outer and inner bodies are structurally independent and represent the separate development of outer and inner walls. In the gonyaulacoid cysts, the outer and inner bodies are structurally more intimately related, and represent the differentiation of a single wall into outer and inner layers.