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 produced a phototrophic vegetative cell that had the typical plate pattern of a Scrippsiella species. The cyst morphotypes, observed in a clonal culture of this species, ranged from cysts with well-developed paratabulation to cysts in which the paratabulation was barely visible, to cysts covered by irregularly shaped crystals. The analysis of thin sections of the calcareous cysts using the polarized light microscope equipped with crossed nicols and a gypsum plate showed that the optical orientation of the calcite crystals was tangential in all the morphotypes examined. We suggest that the crystallographic method we describe might provide insights for calcareous cyst taxonomy and phylogeny .     

NEW CALCAREOUS DINOFLAGELLATES (CALCIODINELLOIDEAE) FROM THE MEDITERRANEAN SEA1

Investigations on calcareous dinoflagellates from surface sediments from the Mediterranean Sea revealed 14 species, including one new genus and four previously undescribed species: Calciodinellum levantinum sp. nov., Calciodinellum elongatum nov. comb., Lebessphaera urania gen. nov. et sp. nov., and Scripp‐ siella triquetracapitata sp. nov. Furthermore, Fuettererella cf. tesserula, so far only known from the fossil record, was found. The cyst–theca relationships of C. levantinum and C. elongatum are given, based on strains established from water samples of the Mediterranean Sea and the Atlantic Ocean. This study gives an insight into the importance of the modern Mediterranean Sea as an unique region concerning calcareous cyst producing dinoflagellates.     

Scrippsiella trochoidea and scrippsiella regalis, nov. comb. (peridiniales, dinophyceae): a comparison

Culture experiments on dinoflagellates from the Atlantic Ocean revealed Scrippsiella regalis (Gaarder) Janofske, nov. comb., a calciodinelloid species with a spherical spiny calcareous cyst. This calcareous cyst was collected previously from plankton and sediment samples, where it was described as the coccolithophorid Discosphaera regalis Gaarder or was often mistaken for the cyst of Scrippsiella trochoidea (von Stein) Loeblich III. The morphological features of both the cellulosic theca and the calcareous cyst of S. trochoidea and S. regalis were compared with respect to their systematic position and the emendation of taxa. Both species were found to have different distribution patterns. Scrippsiella trochoidea is known only from the neritic environment, whereas S. regalis has been found mostly in oceanic samples. The preservation of these spiny calcareous dinocysts in the (fossil) sediment was dependent on the ultrastructure of the calcareous layer of the cyst wall.