Ultrastructure of the flagellar apparatus inPleurochrysis (classPrymnesiophyceae)

Summary The ultrastructure of the flagellar apparatus of aPleurochrysis, a coccolithophorid was studied in detail. Three major fibrous connecting bands and several accessory fibrous bands link the basal bodies, haptonema and microtubular flagellar roots. The asymmetrical flagellar root system is composed of three different microtubular roots (referred to here as roots 1,2, and 3) and a fibrous root. Root 1, associated with one of the basal bodies, is of the compound type, constructed of two sets of microtubules,viz. a broad sheet consisting of up to twenty closely aligned microtubules, and a secondary bundle made up of 100–200 microtubules which arises at right angles to the former. A thin electron-dense plate occurs on the surface of the microtubular sheet opposite the secondary bundle. The fibrous root arises from the same basal body and passes along the plasmalemma together with the microtubular sheet of root 1. Root 2 is also of the compound type and arises from one of the major connecting bands (called a distal band) as a four-stranded microtubular root and extends in the opposite direction to the haptonema. From this stranded root a secondary bundle of microtubules arises at approximately right angle. Root 3 is a more simple type, composed of at least six microtubules which are associated with the basal body. The flagellar transition region was found to be unusual for the classPrymnesiophyceae. The phylogenetic significance of the flagellar apparatus in thePrymnesiophyceae is discussed.