THE CYST-THECA RELATIONSHIP IN CALCIODINELLUM-OPEROSUM EMEND (PERIDINIALES, DINOPHYCEAE) AND A NEW APPROACH FOR THE STUDY OF CALCAREOUS CYSTS

The paratabulate calcareous cyst of Calciodinellum operosum Deflandre was recorded in a sediment trap sample collected in the Bay of Naples (Tyrrhenian Sea, Italy). The germination of this resting stage produce d a phototrophic vegetative cell that had the typical plate pattern of a Scrippsiella species. The cyst morphotypes, observed in a clonal cu lture of this species, ranged from cysts with well-developed paratabul ation to cysts in which the paratabulation was barely visible, to cyst s covered by irregularly shaped crystals. The analysis of thin section s of the calcareous cysts using the polarized light microscope equippe d with crossed nicols and a gypsum plate showed that the optical orien tation of the calcite crystals was tangential in all the morphotypes e xamined. We suggest that the crystallographic method we describe might provide insights for calcareous cyst taxonomy and phylogeny.