Studies on the fine structure of Prasinocladus ascus (Prasinophyceae)

* Contributions from the Shimoda Marine Biological Station, No. 275.

Abstract

Prasinocladus ascus, a member of the Prasinophyceae, was investigated with electron microscopy. The selected aspects of ultrastructure were compared with those of related taxa. Special attention was paid to the structure of pyrenoids in relation to the taxonomy of this algal group. The pyrenoids of P. ascus differ from those of P. marinus by possessing a complicated canalicular system, which is never invaded by the protrusion of the nucleus, but is filled with electron dense substances delimited by a single membrane. This is fundamentally similar to the pyrenoid structure known in Platymonas, particularly P. convolutae (Parke & Manton, 1967). Taking the following two characters into consideration, it would be morenatural to consider that there is a closer relation between P. ascus and P. convolutae: (1) presence of stalked cell compartment possessing no transverse septa; and (2) presence of the third membrane lining cytoplasmic substance in the canalicular system of pyrenoid.