The ultrastructure and taxonomy ofDiacronema vlkianum(Prymnesiophyceae) with special reference to the haptonema and flagellar apparatus

Abstract

The taxonomic position of the golden-brown flagellateDiacronema vlkianumPrauser has hitherto been uncertain. It was first reported by Vlk (1938) from fresh water and a brief description given, particular interest being ascribed to the flagella which staining and light microscopy indicated to be without appendages. Because of this Vlk concluded that the organism, which he did not name, occupied a taxonomic niche somewhat apart from typical chrysophytes. In 1958, Prauser isolated, also from fresh water, a flagellate which he identified as Vlk's organism and he described it using both electron microscopy of shadow-cast cells and optical microscopy of living material. He confirmed the lack of flagellar hairs and discussed the taxonomy ofDiacronemain relation to both the Ochromonadales with heterokont flagella and the genusChrysochromulinaLackey with equal smooth flagella. He suggested that the genus could be thought of as representing a new family, the Diacronemataceae, arising from an ochromonad stock and possibly representing a unique line within the chrysomonads.