FINE-STRUCTURE OF PYRAMIMONAS-CYCLOTRETA SP-NOV (PRASINOPHYCEAE) FROM NORTHERN FOXE BASIN, ARCTIC CANADA, WITH SOME OBSERVATIONS ON GROWTH-RATES

An undescribed species of Pyramimonas, P. cyclotreta from Northern Foxe Basin (Arctic Canada) has been examined by light and electron microscopy of cultured material. Particular emphasis is given to the fine structure of the cell and the periplast. Pyramimonas cyclotreta is a typical member of the subgenus Vestigifera but differs in scale structure. It possesses a type of footprint scales not encountered before in the genus. Pyramimonas cyclotreta also differs in certain cytoplasmic features such as the structure of the posterior end of the cell and the very distinct connection between the flagellar apparatus and the microbody system. The response of growth to different temperatures reveals P. cyclotreta as cold stenothermal. Pyramimonas cyclotreta shows some morphological similarity to P. torta, a species from Belgian waters.